Project 2 - Design and Development of Pulse Oximeter (Medical Technology)

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The global pulse oximeter market size was valued at USD 2.3 billion in 2020 and is expected to expand at a compound annual growth rate (CAGR) of 6.4% from 2021 to 2028. Rising awareness regarding applications of pulse oximeters in COVID-19 management and the increasing prevalence of target diseases is expected to drive the growth of the market.Figure-1.

Availability of new products and high unmet needs in developing and least-developed economies are expected to boost market growth over the forecast period. Around 43 states in the U.S. have made pulse oximetry mandatory for newborn screening and is gaining popularity in other countries due to applications in the detection of Congenital Heart Defects (CHD) and other heart and respiratory conditions.

The growing prevalence of target diseases such as asthma, hyperlipidemia, hypertension, diabetes, ischemic conditions, cardiac arrhythmia, sleep apnea, and COPD is expected to be a major market driver over the forecast period. According to the WHO, around 64 million patients are currently living with COPD worldwide with approximately 90% of deaths due to COPD occurring in low- and middle-income countries.

High-quality pulse oximeters are critical for the early diagnosis and treatment of patients with COVID-19. The manufacturing and supply chains of pulse oximeters are expected to witness challenges during this period, as most of the companies are working at half their production capacities. Furthermore, trade restrictions across highly impacted countries are expected to limit the timely distribution of products. However, manufacturers are working to ensure an adequate supply of fingertip and handheld pulse oximeters to countries in dire need, as cases of COVID-19 continue to increase at an exponential rate.

Type Insights

The handheld segment dominated the market for the pulse oximeter and accounted for the largest revenue share of 38.9% in 2020. The market is primarily driven by the fact that these oximeters are easy to use in case of emergencies. The oxygen saturation level of a patient can strongly influence the course of treatment. A rise in the number of stroke cases and surgeries is anticipated to boost market growth over the forecast period.

Technological advancements in oximeters are expected to drive the segment. Added features such as easy transfer of data, extensive memory, alarm system, and Bluetooth increase the efficiency of products. Industry players introduce new products with additional features to sustain in the competitive market. For instance, in August 2015, Nonin Medical, Inc. launched a wireless fingertip oximeter operated via Bluetooth-NoninConnect Model 3230.

The COVID-19 pandemic has restricted the visits to medical facilities hindering medical care services, and manufacturers are innovating products to provide alternative telehealth solutions. In January 2021, Tyto Care, a telehealth company launched a fingertip pulse oximeter that connects to the TytoCare device via a cable to logging test results to patients EHR enabling its remote monitoring by clinicians.

Report Coverage & Deliverables

Figure-2.

End-use Insights

The hospitals and other healthcare facilities segment dominated the pulse oximeter market and accounted for the largest revenue share of 82.0% in 2020 due to an increase in the number of surgeries and emergency room visits. Long-term care facilities are at high risk of COVID-19 infections, and residents are being continuously monitored for symptoms by checking vital respiratory parameters. Thus, demand for pulse oximeters from home healthcare centers and long-term care facilities is expected to increase during the COVID-19 pandemic.

The homecare segment is expected to witness lucrative growth during the forecast period due to factors such as increasing awareness regarding the importance of monitoring oxygen levels. Fingertip pulse oximeters are considered affordable and effective in homecare, as they can help track and store a patient’s oxygen level readings, which can help reduce the risk of readmission to a hospital. In addition, spot-checking is an effective way for patients suffering from COPD and CHD. Moreover, self-monitoring helps patients actively participate in the management of their health. With an increase in the aging population, the incidence of chronic pulmonary and cardiac conditions is expected to rise. This is anticipated to augment the need for monitoring devices, such as pulse oximeters, in home settings.

Regional Insights

North America dominated the market for the pulse oximeter and held the largest revenue share of 49.1% in 2020, owing to increasing awareness regarding the importance of monitoring respiratory vitals among the common population. Current Procedural Terminology (CPT) recognizes three codes for reimbursement of pulse oximeters: 94760, 94761, and 94762. As the use of pulse oximeter is considered supplementary by Medicare, it is typically reimbursed along with a primary service.

Moreover, for outpatients and patients opting for home settings, a pulse oximeter is considered a reasonable necessity and reimbursed after proper documentation. Thus, a favorable reimbursement infrastructure is expected to contribute to market growth. Moreover, the health organizations are updating medical practitioners with research related to COVID-19 to assist in better management of the pandemic situation. In interim clinical guidance published in February 2021, CDC reported the probability of pulse oximeters having sub-optimal accuracy in dark skin patients.Figure-3.

Recent changes in regulatory norms in Europe are expected to affect all medical device manufacturers. Although factors such as modifications in labeling requirements and changes in rules and regulations pertaining to the distribution of medical devices may slow down the approval process, in the long run, they may result in benefits to approved products, such as improvement in quality and reduction in the number of product recalls.

In Asia Pacific, market players are recognizing the potential and introducing new products suited for developing economies of the region. In January 2017, Masimo launched Rad-97 Pulse-CO Oximeter in India. The product was intended to improve CHD screening in neonates. Although Asia Pacific has a slightly declining birth rate, the number of infants born every day is considerably large. This results in a large target population for CHD.

Key Companies & Market Share Insights

The market is fragmented with the presence of various global and regional manufacturers. The market is expected to adopt various strategies such as product launches and acquisitions by key players to expand their market share. For instance, in January 2020, Vyaire Medical made its MX40-a reusable telemetry adapter-commercially available in the U.S. This product features a SpO2 port, which is compatible with Philips 9 pin pulse oximeter sensor and Masimo LNCS pulse oximeter.

Key industry players are undertaking other major initiatives, such as licensing agreements and strategic partnerships, to strengthen their market presence. In November 2016, the company entered into a partnership with Masimo and withdrew all pending lawsuits against the company. It was also relieved by Masimo from paying the USD 467 million jury verdict. Some of the prominent players in the pulse oximeter market include:

• Medtronic (Covidien)

• Carefusion Corp.

• GE Healthcare

• Philips Healthcare

• Masimo

• CAS Medical Systems, Inc.

• Opto Circuits India Ltd.

• Nonin Medical, Inc.

• Smiths Medical

• Welch Allyn

• Spacelabs Healthcare

• Meditech Equipment Co.

• Nihon Kohden Corporation

Segments Covered in the Report

This report forecasts revenue growth at the global, regional, and country levels and provides an analysis of the latest industry trends in each of the sub-segments from 2016 to 2028. For the purpose of this study, Grand View Research has segmented the global pulse oximeter market report on the basis of type, end-use, and region:

• Type Outlook (Revenue, USD Million, 2016 - 2028)

  • Fingertip

  • Handheld

  • Others

• End-use Outlook (Revenue, USD Million, 2016 - 2028)

  • Hospitals & Other Healthcare Facilities

  • Homecare

• Regional Outlook (Revenue, USD Million, 2016 - 2028)

  • North America

    • U.S.

    • Canada

  • Europe

    • U.K.

    • Germany

    • France

    • Italy

    • Spain

  • Asia Pacific

  • China

  • Japan

  • India

  • Latin America

    • Brazil

    • Mexico

  • Middle East & Africa (MEA)

    • South Africa

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Traditionally, peripheral blood oxygen saturation (SpO₂) is a measurement taken at the peripherals of the body on the finger or ear, most commonly with a clip device to determine the ratio of oxygen saturated hemoglobin to total hemoglobin. This measurement is used to tell how well red blood cells are transporting oxygen from the lungs to other parts of the body. Normal SpO₂ levels vary from 95% to 100% in a healthy adult. Levels below this range indicate a condition known as hypoxemia. This means that the body is not transporting enough oxygen to maintain healthy organs and cognitive function.

A person suffering from hypoxemia may experience dizziness, confusion, shortness of breath, and headaches. Several medical conditions can cause poor blood oxygenation and may require continuous or intermittent monitoring at home or in a clinical setting.

SpO₂ is one of the most common vital signs recorded within a clinical setting. Some conditions that require continuous SpO₂ monitoring include asthma, heart disease, COPD, lung disease, pneumonia, and COVID-19 induced hypoxia.

One of the ways to determine whether symptomatic COVID-19 patients need hos-pitalization is by monitoring their SpO₂ levels. If those levels fall below the baseline number (usually under 92%), they need to be checked into an emergency room.

The Recent Link Between COVID-19 and Hypoxia

Very recently, COVID-19 patients have been diagnosed with a particularly insidious condition known as silent hypoxia. Silent hypoxia can do severe damage to the body before any of the typical COVID-19 respiratory symptoms, like shortness of breath, occur. An article on the National Center for Biotechnology Information website¹ states “the ability to detect this silent form of hypoxia in COVID-19 patients before they begin to experience shortness of breath is critical for preventing the pneumonia from progressing to a dangerous level.”

SpO₂ monitoring is also a key indicator in diagnosing sleep apnea. Obstructive sleep apnea causes the airways to become partially or fully blocked during sleep. This can be observed as long pauses in breathing or periods of shallow breathing causing temporary hypoxia. If untreated over time, sleep apnea can increase the likelihood of heart attack, stroke, and obesity. It is estimated that sleep apnea affects between 1% to 6% of the total adult population.

The Urgent Need for a Better Pulse Oximeter Now and in the Future

As patient care trends toward ambulatory and in-home monitoring, there is a need to develop vital sign monitoring devices that will not impede users from completing daily tasks. In the case of SpO₂, monitoring areas other than the finger and ear will present a host of design challenges. The recent emergence of silent hypoxia makes the case for development of more portable clinical-grade pulse oximeter units even more compelling.

This article will explain some of the fundamental principles of SpO₂ measurement and introduce ADI’s latest generation of optical AFEs, the ADPD4100 and ADPD4101, which reduce design complexities for medical grade SpO₂ devices. Built-in high performance automatic ambient light rejection reduces the burden on mechanical and electronic design. The high dynamic range in the ADPD4100 at lower power consumption reduces the number of photodiodes or LED current in a design to determine slight variations in patient SpO₂ level efficiently. Finally, digital integrator options allow users to enter an extremely efficient power consumption mode to enable longer run times in portable PPG solutions by disabling analog blocks in the optical signal path.

What Is Oxygen Saturation?

Oxygen saturation is the percentage of oxygen saturated hemoglobin within the blood with respect to the total available hemoglobin. The gold standard for measuring oxygen saturation is the atrial blood oxygenation measurement, SaO₂. However, this method requires laboratory-based blood gas analysis of a blood sample. The calibration section covers this in greater depth.

SpO₂ is an estimate of the oxygen saturation levels measured at the peripherals of the body, using a pulse oximeter. Until recently, the most common way to measure oxygen saturation has been to use a pulse oximeter positioned on the finger.

How Does a Pulse Oximeter Work?

A pulse oximeter works on the principal that absorption of light in oxygenated hemoglobin (HbO₂) and deoxygenated hemoglobin (RHb) differ significantly at specific light wavelengths. Figure 1 shows the extinction coefficient of HbO₂, Hb, and methemoglobin (MetHb) across the visible and infrared light spectrum. The extinction coefficient is a measurement of how strongly a chemical substance absorbs light at a given wavelength. From Figure 1, it can be seen that HbO₂ absorbs more red light (600 nm) and allows more infrared light (940 nm) to pass through. RHb absorbs more light at infrared wavelengths, which allows more red light to pass through than in HbO₂.

The most basic pulse oximeter consists of two LED (one red 660 nm LED and one infrared (IR) 940 nm LED) and a single photodiode (PD) in a reflective or transmissive configuration (see Figure 4). The pulse oximeter will pulse the red LED and measure the resulting signal on the PD. Repeat this for the IR LED and finally with both LEDs off to get a baseline for any ambient external light sources. This generates a photoplethysmography (PPG) signal for both wavelengths.

Figure-4.

Figure-5.Basic pulse oximeter circuit.

The signal contains DC and AC components. The DC component is due to constant reflective matter such as skin, muscle and bone, and venous blood. When a body is at rest and motion is less of a factor, the AC component comprises mainly of reflected light from the pulsation of artery blood. The AC component depends on heart rate and artery thickness, with more reflected or transmitted light in systolic (pump) than the dystopic (relaxation). During the systolic phase, blood is pumped from the heart, which increases atrial blood pressure. The increase in blood pressure expands the arteries and leads to an increase in atrial blood volume. This increase in blood causes an increase in light absorption. Blood pressure drops during the diastolic phase and therefore so does the absorption of light. Figure 3 shows the diastolic trough and systolic peaks caused by the beating heart.

The Beer-Lambert law explains that light decays exponentially when travelling though absorptive material. This can be used to determine the level of oxygenated hemoglobin to total hemoglobin.

The intensity of light absorbed at the diastole and systole are related by:

Where α measures the absorption rate of light in atrial blood and d2 is the AC amplitude of the PPG signal (see Figure 3). I_diastole is equal to the DC component labelled d1.

Light attenuation through tissue. Figure-6.

By computing AC and DC from a PPG signal, we are able to determine the change in absorption of light in atrial blood –α.d2 caused by blood pumping from the heart, with no contribution from other tissue.

The ratio of the AC component to the DC component is known as the perfusion index, which is the ratio of the pulsating blood flow to the nonpulsatile static blood flow. The goal of a PPG-based heart rate or SpO₂ measurement system is to increase the AC to DC signal ratio.

PI = AC/DC

The perfusion index for infrared and red wavelengths can be used to calculate the ratio of ratios (RoR), which is the ratio of PI_red to PL_ir. As the absorption of the light at a given wavelength is proportional to the

In theory, the RoR can be substituted into the following formula to compute SpO₂:

Where: E_HbO2,red = extinction coefficient of HbO₂ at 600 nm, E_HbO2,ired = extinction coefficient of HbO₂ at 940 nm

E_RHb,ired = extinction coefficient of RHb at 940 nm, E_RHb,red = extinction coefficient of RHb at 600 nm

However, the Beer-Lambert law cannot be used directly as there are a number of variable factors in every optical design that cause variations to the RoR to SpO₂ relationship. These include mechanical baffle design, LED to PD spacing, electronic and mechanical ambient light rejection, PD gain errors, and many more.

To obtain clinical grade accuracy from a PPG-based SpO₂ pulse oximeter, a lookup table or algorithm must be developed for the correlation between RoR and SpO₂.

Calibration

Calibration of the measurement system is required to develop a high accuracy SpO₂ algorithm. To calibrate an SpO₂ system, a study must be completed where a participant’s blood oxygen levels are medically reduced, monitored, and overseen by a medical professional. This is known as a hypoxia study.

The SpO₂ measurement system can only be as accurate as the reference. Reference options include medical grade finger clip pulse oximeters and the gold standard co-oximeter. The co-oximeter is an invasive method of measuring the oxygen saturation of blood that yields high accuracy, but in most cases is not convenient to administer.

The calibration process is used to generate a best fit curve of RoR value calculated from the optical SpO₂ device to the co-oximeter SaO₂ measurement. This curve is used to generate a lookup table or equation for calculating SpO₂.

Calibration will be required for all SpO₂ designs as RoR is dependent on a number of variables such as LED wavelength and intensity, PD response, body placement, and ambient light rejection, which will differ with each design.

An increased perfusion index and, in turn, a high AC dynamic range on the red and IR wavelengths will increase the sensitivity of the RoR calculation and, in turn, return a more accurate SpO₂ measurement.

During a hypoxia study, 200 measurements equally spaced between 100% and 70% blood oxygen saturation need to be recorded. Subjects are chosen with a variety of colored skin tone, and an equal spread of age and gender. This variation in skin tone, age, and gender accounts for differing perfusion index results from a spread of individuals.

The overall error for transmissive pulse oximeters must be ≤3.0% and ≤3.5% for reflective configuration.

Design Considerations:

Transmissive vs. Reflective

A PPG signal can be obtained using a transmissive or reflective LED and PD configuration. A transmissive configuration measures the nonabsorbed light passed through a part of the body. This configuration is best suited to areas such as the finger and earlobe where measurement benefits from the capillary density of these body locations, which make the measurements more stable, repetitive, and less sensitive to variations in placement. Transmissive configurations achieve a 40 dB to 60 dB increase in the perfusion index.

Reflective PPG configurations are chosen when the PD and LED must be placed next to each other for practicality, such as with wrist- or chest-worn devices.

Figure-7.

LED-PD configuration.

Sensor Positioning and Perfusion Index

Positioning on the wrist and chest require greater dynamic range in the PPG AFE as the DC signal is greatly increased due to the depth of the arteries below static reflective components such as skin, fat, and bone.

Greater resolution in the PPG measurements will reduce the uncertainty in the SpO₂ algorithm. With a typical PI of 1% to 2% for wrist-worn SpO₂ sensors, the goal of pulse oximeter design is to increase the PI through mechanical design or to increase the dynamic range.

The spacing of the LED to PD will have a major effect on the PI. Too little spacing will increase LED to PD crosstalk or backscatter. This will appear as a DC signal and saturate the AFE.

Increasing this spacing reduces the effect of both backscatter and crosstalk but also reduces the current transformer ratio (CTR), which is the LED output to PD return current. This will affect the efficiency of the PPG system and require greater LED power to maximize the AFE dynamic range.

Rapidly pulsing one or multiple LEDs has the benefit of reducing the 1/f noise contribution to the overall signal. Pulsing the LEDs also makes it possible to use synchronized modulation at the receive side to cancel out ambient light interferers. Integrating multiple pulses increases the PD signal amplitude and lowers the average current consumption. Increasing the total PD area also increases CTR as more of the reflective light is captured.

For heart rate PPG measurement, a combination of a single large PD and multiple power efficient green LEDs has been adopted by many HR device manufacturers to be used on places where there is limited blood flow. Green LEDs are chosen due to their high rejection of motion artifacts.² However, this comes at the cost of power. Green LEDs have a higher forward voltage than red and IR and high absorbance in human tissue, meaning a higher LED power is required to return meaningful cardiac information.

As SpO₂ requires multiple wavelengths and most systems still incorporate high efficiency green LEDs for the HR PPG, the most common configuration for HR and SpO₂ PPG systems is a single green, red, and IR LED array surrounded by multiple PDs, as seen on the ADI VSM watch in Figure 5. PD to LED spacing has been opti-mized to reduce backscatter and the baffle design reduces LED to PD crosstalk.

Multiple prototypes of the ADI VSM watch were trialed to verify the most efficient PD to LED spacing for our HR PPG and SpO₂ measurement.

Figure-8.

ADI VSM watch V4, baffle, and LED DP array

Motion Artifacts

Motion artifacts provide one of the greatest design challenges to a PPG measurement system. When motion is present, the width of the arteries and veins change due to pressure. The amount of light absorbed by the photodiode changes and this is present on the PPG signal because photons are absorbed or reflected differently than when a body is at rest.

For an infinitely wide photodiode area covering an infinitely long deep tissue sample, all photons will eventually be reflected to the photodiode. In this case, no artifact due to motion will be detected. This, however, cannot be achieved; the solution is to increase the photodiode area while taking capacitance into account—lowering AFE and providing filtering for motion artifacts.

The normal frequency for a PPG signal is between 0.5 Hz to 5 Hz while motion artefacts are typically between 0.01 Hz to 10 Hz. Simple band-pass filtering techniques cannot be used to remove motion artifacts from the PPG signal. To achieve high accuracy motion cancellation, an adaptive filter needs to be supplied with highly accurate motion data. For this purpose, Analog Devices has developed the ADXL362 3-axis accelerometer. This accelerometer provides 1 mg resolution with up to 8 g of range while consuming only 3.6 μW at 100 Hz and is available in a 3 mm × 3 mm package.

ADI Solution: ADPD4100

The positioning of the pulse oximeter generates several challenges. Wrist-worn SpO₂ devices provide additional design challenges as the AC signal of interest is only 1% to 2% of the total received light on the PD. To achieve medical grade certification and distinguish between slight variations in oxyhemoglobin levels, a higher dynamic range on the AC signal is required. This can be achieved by reducing ambient light interference and decreasing LED driver and AFE noise. ADI has addressed this problem with the ADPD4100.

The ADPD4100 and ADPD41001 achieve up to 100 dB SNR. This increased dynamic range is essential to measure SpO₂ under low perfusion scenarios. This integrated optical AFE has eight onboard low noise current sources and eight separate PD inputs. The digital timing controller has 12 programmable timing slots that enable the user to define an array of PD and LED sequences with specific LED current, analog and digital filtering, integration options, and timing constraints.

A key benefit of the ADPD4100 is the increase in SNR/μW, which is an important parameter for battery-powered continuous monitoring. This key metric has been addressed by increasing the AFE dynamic range while also lowering the AFE current consumption. The ADPD4100 now boasts a total power consumption of only 30 μW for a 75 dB, 25 Hz continuous PPG measurement including the LED supply. Increasing the number of pulses per sample (n) will result in a (√n) increase in SNR while increasing the LED drive current will have a proportional increase in SNR. 1 μW total system consumption will return 93 dB SNR for a continuous PPG measurement using a 4 V LED supply.

Automatic ambient light rejection reduces the burden on the host microprocessor while achieving 60 dB of light rejection. This is achieved using LED pulses as fast as 1 μs in conjunction with a band-pass filter to reject interference. In certain operating modes, the ADPD4100 automatically calculates the photodiode dark current or LED off state. This result is subtracted from the LED on state before conversion in the ADC to remove ambient light as well as gain errors and drift within the photodiode.

The ADPD4100 is supported with the EVAL-ADPD4100-4101 wearable evaluation kit along with the ADI Vital Signs Monitoring Study Watch. This hardware seamlessly connects to the ADI Wavetool application to enable bioimpedance, ECG, PPG heart rate, and multiwavelength PPG measurements for SpO₂ development.

Embedded in the study watch is an automatic gain control (AGC) algorithm for the ADPD4100 that tunes the TIA gain and LED current to deliver optimum AC signal dynamic range for all LED wavelengths selected.

ADPD410X block diagram.Figure-9.

ADPD4100 simultaneous red (right) and IR (left) PPG measurement. Figure-10.

Alternative ADI Solutions

Finger- and earlobe-based SpO₂ readings are the easiest to design for as the signal-to-noise ratio is higher than wrist- or chest-based positioning due to the reduction in bone and tissue, which also reduces the DC component contribution.

For such applications, the ADPD144RI module and the ADPD1080 are suitable devices.

The ADPD144RI is a complete module with an integrated red 660 nm LED and 880 nm IR LED and four PDs in a 2.8 mm × 5 mm package. The spacing between the LEDs and PD have been optimized to give the best signal-to-noise ratio for SpO₂ high accuracy PPG measurements. This module allows users to quickly skip the design challenges associated with LED and PD placement and spacing to achieve optimal power to noise ratios. The ADPD144RI mechanically has been optimized to reduce optical crosstalk as much as possible. This provides a solid solution, even when the sensor is placed under a single glass window.

The ADPD1080 is an integrated optical AFE with three LED drive channels and two PD current input channels in a 17-ball, 2.5 mm × 1.4 mm WLLCSP. This AFE is ideal for custom design low channel count PPG products where board space is critical.

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Figure-1.

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Figure-2.

Modular versus Integral Product Architecture: the arrangement where functions of the product are done by an array of parts that need not be organized or arranged in assemblies are described by the integral design whereas in the modular design particular functions necessary for achieving the overall purpose

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Pulse oximeter.

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Figure-3.

Failure Mode And Effects Analysis

FMEA is mostly used by upper management or stakeholders. In practice, the testers get little insight into this technique. But now the trend is changing and I feel if the testers understand this concept properly, they can drive their thought process of writing test cases to one level up by utilizing this technique to:

• Understand the stakeholder’s goals of testing the application.
• Understand the business.
• Derive the high-level test scenarios based on business and management interest.
• Derive effective test cases that provide better coverage to the risk-prone areas.
• Prioritize the test cases.
• Decide what to test and what to defer at any phase.
  

Background

RISK ANALYSIS is a crucial aspect of Test Management. The question then arises – What is Risk Analysis? And why is it important? To understand this, it is vital to understand – what is RISK?

See Also => Types of Risks in Software Projects.

RISK as its literal meaning is a possibility of a negative or undesirable outcome or event. Risks if not handled or managed properly may lead to poor quality, unsatisfied customers and sometimes loss of business.

Risk has 2 attributes:

• Probability
• Impact

Probability means the chances of a particular risk to occur and impact means the extent of the effect of the risk.

What Is Risk Analysis?

Risk Analysis is a mechanism by which the identified potential risks are analyzed & studied thoroughly in order to find the probability and impact. It is advisable to measure the two attributes and based on the result we identify:

• What to test first?
• What to test more?
• What not to test(This time)?

There are many methods of doing the Risk Analysis and they are broadly classified into two types:

• Informal Techniques: These are based on experience, judgment, and intuition.
• Formal Techniques: Identifying and weighing risk attributes.

Failure Mode And Effects Analysis (FMEA): This is a formal method of doing a Risk Analysis. In the following sections, I will be discussing more on FMEA and try to elaborate it with the example.

FMEA is a formal technique of doing Risk Analysis. It is a systematic and quantitative tool in the form of a Spread Sheet that assists the members to analyze what might get wrong. To do the FMEA we require the right people on the table. It requires a representative from all walks of the industry including customers.

Description

FMEA starts and continues with Brainstorming sessions. Participants need to identify all the components, modules, dependencies, limitations that could fail in a production environment and eventually lead to poor quality, reliability and may result in loss of business.

During FMEA we not only identify the extent of the loss but also try to identify the cause of those failures. To measure FMEA, we require 3 attributes:

• Severity of the Failure (S)
• Priority of the Failure (P)
• Likelihood of the Failure (L)

We put each of these attributes in a scale shown below:

Severity Scale:

Priority scale:

Likelihood scale:

All these three attributes (Severity, Priority, and Likelihood) are individually measured in scale and then multiplied to get a Risk Priority Number (RPN).

i.e. Risk Priority Number (RPN) = S*P*L

Based on this RPN value, we determine the extent of testing. Lesser is the RPN, higher is the Risk.

Let’s try to understand it with an example:

Failure Mode Effect Analysis Example

(This is a hypothetical example only for an understanding purpose. Actual implementation and features may vary)

Let’s consider a simple example of a banking application that has 4 features.

• Feature 1: Withdraw
• Feature 2: Deposit
• Feature 3: Home Loan
• Feature 4: Fixed Deposits.

A Risk Analysis team is formed which consists of the Bank manager, UAT Test Manager ( representing end-user), Technical Architect, Test Architect, Network Administrator, DBA, and a Project Manager.

After a series of brainstorming sessions the team came up with the following Risks:

• Complex Business logic in case of calculating interest rate of the home loan.
• The system fails at 200 concurrent users.
• The system fails to handle documents which are more than 6 MB.

Now let’s try to calculate the Severity, Priority, and Likelihood of these identified risks.

Severity:

Priority:

Likelihood:

Now let’s put all these attributes together:

Now let’s calculate the Risk Priority Number (RPN = Severity * Priority * Likelihood)

Now the key is: Lower is the RPN – Higher is the risk.

So here for this particular example, Feature 1 (Complex business logic in case of calculating the interest rate of the home loan) has the highest risk and feature 2 (System fails at 200 concurrent users) has the lowest risk.

How to use this to derive test cases?

Since Feature 1 is the riskiest feature, the test cases should be rigorous and more in-depth. Write the test cases to cover complete functionality and affecting modules by the feature. Use all sorts of test case writing techniques (Equivalence Partitioning and BVA, Cause and effect graph, State Transition diagram) to derive the test cases.

The test cases should not only be functional but also non-functional (Load test, Stress, and Volume test, etc.). Basically, we need to do exhaustive testing of this particular feature, so base your test cases accordingly. Also, consider all the dependent modules on this important feature.

Feature 2 is the LEAST RISKY feature, so base your test cases on the major functionality. Just high-level test cases to validate that the feature works as expected should be sufficient.

Feature 3 is a MODERATE RISK feature, so base your test cases to cover all the major and dependent functionality. Write some BVA test cases to validate a few negative scenarios as well. The extent of the test cases should be between High risk and Low-risk factor. If required, include few non-functional test cases as well.

FMEA And Degree Of Testing

Based on the RPN value, we determine the extent or degree of testing to be done.

Normally if:

• RPN is between 1-10, we do Extensive Testing (Covering in and out of the feature/module)
• RPN is between 11-30, we do Balanced Testing ( Covering all the major functionality of the feature/module)
• RPN is between 31-70, we do Opportunity testing (Covering the basic functionality of the feature/module)
• RPN is more than 70 – No testing or when time permits, only anomaly reporting.

These ranges or numbers are not restricted to the ones I mentioned above. They may vary as per the nature of the project.

Resources: Download FMEA Software and FMEA Template.

Conclusion

Risk Analysis using FMEA requires time and experience. Desired results can be achieved only by equal participation from all the responsible team members. Though this technique is formal, it requires a series of brainstorming sessions and it is equally important to document all the identified risks.

Since most of the applications are exclusive, the scale to measure the parameters of FMEA (i.e. Priority, Severity, and Likelihood) also dependents on the application. If done appropriately, there are many advantages to the FMEA technique. It can be used for identifying potential risks and based on this team can plan an effective mitigation strategy.

The current study was conducted at Assiut University Hospital. Enrolment criteria included all patients diagnosed with heart failure and admitted to the Intermediate Cardiology Care Unit (ICCU), Internal Medicine Department, from July 1^st, 2018 to 31^st December 2019. Exclusion criteria included: i) patients with core body temperature <36°C; ii) patients with metabolic acidosis (serum lactate level >2 mmol/L); iii) those who developed cardiogenic shock; and iv) patients with diseases or conditions known to affect pulse oximeter accuracy, e.g., sickle cell disease, methemoglobinemia, carboxyhemoglobinemia. Enrolled subjects were subjected to full clinical evaluation including smoking history and medical comorbidities. Age and gender-matched control groups were enrolled.

The pulse oximeter used was a Philips M1020A pulse oximetry module (Philips Medical Systems, Eindhoven, Netherlands). An appropriate-sized pulse oximeter sensor (Phillips M1020A/ M1192A/ M1194A/ M1195A) was applied to the finger, on the toe, and the ear lobe.

Patients were continuously monitored by pulse oximetry during their stay in the ICCU. The target SpO₂ was ‘morning baseline SpO₂’, which was registered by nurses in awake patients on the morning round, usually after chest radiography, and taking the most stable value on room air. For patients receiving oxygen therapy, it was recorded when a steady value was reached, after several minutes of oxygen discontinuation.

At the same time, an arterial blood sample was drawn. A single reading of SpO₂ was taken in individual sensor locations after the pulse oximeters had achieved optimal plethysmography signals and heart rates matching with the electrocardiogram (ECG) monitor (CMS; Philips Medical Systems). In those patients with variable heart rate(s), readings of SPO₂ were taken after control of their abnormal heart rates. Simultaneously, an arterial blood gas (ABG) analysis was done for co-oximetric measurement of SaO₂ using an ABL 800 FLEX ABG machine (Radiometer America Inc., Cleveland, OH, USA). The core temperature, arterial pressure, heart rate, and ABG value of hemoglobin were recorded simultaneously.

Comparison of pulse oximetry reading (SpO₂) with arterial oxygen saturation (SaO₂) was reported in terms of bias and precision as described by Bland and Altman [7]. Bias is the difference between the specific body location SpO₂ (finger, toe, ear) and SaO₂ (i.e., SpO₂-SaO₂) and precision is the ±1 standard deviation of the difference [7]. A low bias in a sensor site implies that the pulse oximeter sensor gives a more accurate reading at that site and vice versa. Precision implies the reproducibility of the measurement.

Statistical analysis

Data were described as mean ± standard deviation (SD) and frequencies if they are quantitative or qualitative, respectively. Mann-Whitney test and Wilcoxon Signed Ranks test were used for comparison of quantitative variables among two independent and dependent groups, respectively. Chi-Square test was used for comparison of the distribution of qualitative variables among different groups. Correlation between continuous variables was performed using Spearman’s correlation coefficient. Kruskal-Wallis test was used to compare the bias of two sensor sites statistically. A p<0.05 was interpreted as significant. The SPSS (Statistical Package for Social Science) software v. 20 was used for statistical analysis.

Definition of “detection”

The Oxford English dictionary defines “detection” as “the action or process of identifying the presence of something concealed.”

What is the definition of “Detection” in an FMEA?

“Detection” is a ranking number associated with the best control from the list of detection-type controls, based on the criteria from the detection scale. The detection ranking considers the likelihood of detection of the failure mode/cause, according to defined criteria. Detection is a relative ranking within the scope of the specific FMEA and is determined without regard to the severity or likelihood of occurrence.

How is “Detection” assessed in FMEAs?

For each cause, The FMEA team assesses the detection ranking. This is the likelihood that the current detection-type controls will be able to detect the cause of the failure mode.

For Design FMEAs, detection is the ranking number corresponding to the likelihood that the current detection-type Design Controls will detect the failure mode/cause, typically in a timeframe before the product design is released for production. For Process FMEAs, detection is the ranking number corresponding to the likelihood that the current detection-type Process Controls will detect the failure mode/cause, typically in a timeframe before the part or assembly leaves the manufacturing or assembly plant.

A suggested approach is assuming the failure has occurred and then assessing the capability of the detection-type design or process control to detect the failure mode or cause. If there is no detection-type control for a given failure mode/cause, the detection ranking should be set to the highest level.

Chapter 6 of Effective FMEAs discusses an exception to this definition of detection for application in industries where the emphasis needs to be on detecting failures once the customer takes ownership (or the system is in operation).

What does a Detection Scale look like for Design FMEAs?

The following is an example of a detection scale for Design FMEAs. It is based on “Potential Failure Mode and Effects Analysis (FMEA) 4th Edition, 2008 Manual.”

What does a Detection Scale look like for Process FMEAs?

The following is an example of a detection scale for Process FMEAs. It is based on “Potential Failure Mode and Effects Analysis (FMEA) 4th Edition, 2008 Manual.”

What is an example of Detection in a Design FMEA?

[In this fictitious example, the detection ranking is assessed based on considering the criteria in the AIAG 4 scale and an estimate of a “moderately high” likelihood that the detection-type controls in the Design FMEA will detect the failure mode / cause.]

Item: Power steering pump

Function: Delivers hydraulic power for steering by transforming oil pressure at inlet ([xx] psi) into higher oil pressure at outlet [yy] psi during engine idle speed

Failure Mode: Inadequate outlet pressure (less than [yy] psi)

Effect (Local: Pump): Low pressure fluid goes to steering gear
Effect (Next level: Steering Subsystem): Increased friction at steering gear
Effect (End user): Increased steering effort with potential accident during steering maneuvers

Severity: 10

Cause: Fluid incorrectly specified (viscosity too low)

Occurrence: 5

Prevention Control: Design guidelines for hydraulic fluid selection
Detection Control: Vehicle durability testing #123

Detection: 4

What is an example of a Detection in a Process FMEA?

[In this fictitious example, the detection ranking is assessed based on considering the criteria in the AIAG 4 scale and an estimate of a “very low” likelihood that the detection-type controls in the Process FMEA will detect the failure mode / cause.]

Process Step: Induction harden shafts using induction hardening machine

Function: Induction harden shafts using induction-hardening machine ABC, with minimum hardness Brinell Hardness Number (BHN) “X”, according to specification #123.

Failure Mode: Shaft hardness less than BHN “X”

Effect (In plant): 100% scrap
Effect (End user): Shaft fractures with complete loss of performance
Effect (Assembly): Not noticeable during assembly

Severity: (Customer Effect): 8 (loss of primary function)
Severity: (Mfg/Assy Effect): 8 (major disruption)

Cause: Induction machine electrical voltage/current settings incorrect for part number

Occurrence: 3

Prevention Control: Shaft hardening setup instructions
Detection Control: audit of shaft hardness

Detection: 7

Application Tip

The most common misunderstanding or misapplication of the detection scale is to confuse or co-mingle the three types of detection risk:

1. Likelihood of detection by the identified controls – specifically, what is the likelihood that the current detection-type control will be able to discover the failure mode or its cause (remote, low, moderate, high, etc.)
2. Timing of the opportunity for detection – specifically, what is the timing of the current detection-type control (prior to design freeze, post design freeze, in service, etc.)
3. Type of test used to detect the cause of the problem – what is the quality of test method used to detect the failure mode or its cause (degradation test, test to failure, pass/fail test, etc.)

The detection scale must clearly identify which of the three types of detection risk is being assessed by the individual criteria of the scale.

Next Article

Can you find the error in detection ranking in the example problem for next week? It is a common error, highlighted in the intermediate problem. In the advanced problem, the topic of an in-service detection scale will challenge the most experienced readers.

Inside FMEA Questions & Email List

Ask a question about FMEA

In the words of Albert Einstein, "The Important thing is never to stop questioning." I invite you to ask anything at all about the broad subject of FMEAs. You may be curious about an application issue or want another view on a challenge you are experiencing. Questions and answers are the lifeblood of learning, and we're all learning. I will answer all questions to the best of my ability and promise to keep personal information confidential.

Figure-4.

Background Genome-wide association studies (GWAS) based on single nucleotide polymorphisms (SNPs) revolutionized our perception of the genetic regulation of complex traits and diseases. Copy number variations (CNVs) promise to shed additional light on the genetic basis of monogenic as well as complex diseases and phenotypes. Indeed, the number of detected associations between CNVs and certain phenotypes are constantly increasing. However, while several software packages support the determination of CNVs from SNP chip data, the downstream statistical inference of CNV-phenotype associations is still subject to complicated and inefficient in-house solutions, thus strongly limiting the performance of GWAS based on CNVs. Results CONAN is a freely available client-server software solution which provides an intuitive graphical user interface for categorizing, analyzing and associating CNVs with phenotypes. Moreover, CONAN assists the evaluation process by visualizing detected associations via Manhattan plots in order to enable a rapid identification of genome-wide significant CNV regions. Various file formats including the information on CNVs in population samples are supported as input data. Conclusions CONAN facilitates the performance of GWAS based on CNVs and the visual analysis of calculated results. CONAN provides a rapid, valid and straightforward software solution to identify genetic variation underlying the 'missing' heritability for complex traits that remains unexplained by recent GWAS.

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Traditionally, peripheral blood oxygen saturation (SpO₂) is a measurement taken at the peripherals of the body on the finger or ear, most commonly with a clip device to determine the ratio of oxygen saturated hemoglobin to total hemoglobin. This measurement is used to tell how well red blood cells are transporting oxygen from the lungs to other parts of the body. Normal SpO₂ levels vary from 95% to 100% in a healthy adult. Levels below this range indicate a condition known as hypoxemia. This means that the body is not transporting enough oxygen to maintain healthy organs and cognitive function.

A person suffering from hypoxemia may experience dizziness, confusion, shortness of breath, and headaches. Several medical conditions can cause poor blood oxygenation and may require continuous or intermittent monitoring at home or in a clinical setting.

SpO₂ is one of the most common vital signs recorded within a clinical setting. Some conditions that require continuous SpO₂ monitoring include asthma, heart disease, COPD, lung disease, pneumonia, and COVID-19 induced hypoxia.

One of the ways to determine whether symptomatic COVID-19 patients need hos-pitalization is by monitoring their SpO₂ levels. If those levels fall below the baseline number (usually under 92%), they need to be checked into an emergency room.

The Recent Link Between COVID-19 and Hypoxia

Very recently, COVID-19 patients have been diagnosed with a particularly insidious condition known as silent hypoxia. Silent hypoxia can do severe damage to the body before any of the typical COVID-19 respiratory symptoms, like shortness of breath, occur. An article on the National Center for Biotechnology Information website¹ states “the ability to detect this silent form of hypoxia in COVID-19 patients before they begin to experience shortness of breath is critical for preventing the pneumonia from progressing to a dangerous level.”

SpO₂ monitoring is also a key indicator in diagnosing sleep apnea. Obstructive sleep apnea causes the airways to become partially or fully blocked during sleep. This can be observed as long pauses in breathing or periods of shallow breathing causing temporary hypoxia. If untreated over time, sleep apnea can increase the likelihood of heart attack, stroke, and obesity. It is estimated that sleep apnea affects between 1% to 6% of the total adult population.

The Urgent Need for a Better Pulse Oximeter Now and in the Future

As patient care trends toward ambulatory and in-home monitoring, there is a need to develop vital sign monitoring devices that will not impede users from completing daily tasks. In the case of SpO₂, monitoring areas other than the finger and ear will present a host of design challenges. The recent emergence of silent hypoxia makes the case for development of more portable clinical-grade pulse oximeter units even more compelling.

This article will explain some of the fundamental principles of SpO₂ measurement and introduce ADI’s latest generation of optical AFEs, the ADPD4100 and ADPD4101, which reduce design complexities for medical grade SpO₂ devices. Built-in high performance automatic ambient light rejection reduces the burden on mechanical and electronic design. The high dynamic range in the ADPD4100 at lower power consumption reduces the number of photodiodes or LED current in a design to determine slight variations in patient SpO₂ level efficiently. Finally, digital integrator options allow users to enter an extremely efficient power consumption mode to enable longer run times in portable PPG solutions by disabling analog blocks in the optical signal path.

What Is Oxygen Saturation?

Oxygen saturation is the percentage of oxygen saturated hemoglobin within the blood with respect to the total available hemoglobin. The gold standard for measuring oxygen saturation is the atrial blood oxygenation measurement, SaO₂. However, this method requires laboratory-based blood gas analysis of a blood sample. The calibration section covers this in greater depth.

SpO₂ is an estimate of the oxygen saturation levels measured at the peripherals of the body, using a pulse oximeter. Until recently, the most common way to measure oxygen saturation has been to use a pulse oximeter positioned on the finger.

How Does a Pulse Oximeter Work?

A pulse oximeter works on the principal that absorption of light in oxygenated hemoglobin (HbO₂) and deoxygenated hemoglobin (RHb) differ significantly at specific light wavelengths. Figure 1 shows the extinction coefficient of HbO₂, Hb, and methemoglobin (MetHb) across the visible and infrared light spectrum. The extinction coefficient is a measurement of how strongly a chemical substance absorbs light at a given wavelength. From Figure 1, it can be seen that HbO₂ absorbs more red light (600 nm) and allows more infrared light (940 nm) to pass through. RHb absorbs more light at infrared wavelengths, which allows more red light to pass through than in HbO₂.

The most basic pulse oximeter consists of two LED (one red 660 nm LED and one infrared (IR) 940 nm LED) and a single photodiode (PD) in a reflective or transmissive configuration (see Figure 4). The pulse oximeter will pulse the red LED and measure the resulting signal on the PD. Repeat this for the IR LED and finally with both LEDs off to get a baseline for any ambient external light sources. This generates a photoplethysmography (PPG) signal for both wavelengths.

The signal contains DC and AC components. The DC component is due to constant reflective matter such as skin, muscle and bone, and venous blood. When a body is at rest and motion is less of a factor, the AC component comprises mainly of reflected light from the pulsation of artery blood. The AC component depends on heart rate and artery thickness, with more reflected or transmitted light in systolic (pump) than the dystopic (relaxation). During the systolic phase, blood is pumped from the heart, which increases atrial blood pressure. The increase in blood pressure expands the arteries and leads to an increase in atrial blood volume. This increase in blood causes an increase in light absorption. Blood pressure drops during the diastolic phase and therefore so does the absorption of light. Figure 3 shows the diastolic trough and systolic peaks caused by the beating heart.

The Beer-Lambert law explains that light decays exponentially when travelling though absorptive material. This can be used to determine the level of oxygenated hemoglobin to total hemoglobin.

The intensity of light absorbed at the diastole and systole are related by:

Where α measures the absorption rate of light in atrial blood and d2 is the AC amplitude of the PPG signal (see Figure 3). I_diastole is equal to the DC component labelled d1.

By computing AC and DC from a PPG signal, we are able to determine the change in absorption of light in atrial blood –α.d2 caused by blood pumping from the heart, with no contribution from other tissue.

The ratio of the AC component to the DC component is known as the perfusion index, which is the ratio of the pulsating blood flow to the nonpulsatile static blood flow. The goal of a PPG-based heart rate or SpO₂ measurement system is to increase the AC to DC signal ratio.

PI = AC/DC

The perfusion index for infrared and red wavelengths can be used to calculate the ratio of ratios (RoR), which is the ratio of PI_red to PL_ir. As the absorption of the light at a given wavelength is proportional to the

In theory, the RoR can be substituted into the following formula to compute SpO₂:

Where: E_HbO2,red = extinction coefficient of HbO₂ at 600 nm, E_HbO2,ired = extinction coefficient of HbO₂ at 940 nm

E_RHb,ired = extinction coefficient of RHb at 940 nm, E_RHb,red = extinction coefficient of RHb at 600 nm

However, the Beer-Lambert law cannot be used directly as there are a number of variable factors in every optical design that cause variations to the RoR to SpO₂ relationship. These include mechanical baffle design, LED to PD spacing, electronic and mechanical ambient light rejection, PD gain errors, and many more.

To obtain clinical grade accuracy from a PPG-based SpO₂ pulse oximeter, a lookup table or algorithm must be developed for the correlation between RoR and SpO₂.

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Sustainability is an increasingly important requirement for human activity, making sustainable development a key objective in human development. At its core, sustainable development is the view that social, economic and environmental concerns should be addressed simultaneously and holistically in the development process.

Sustainability has been applied to many fields, including engineering, manufacturing and design. Manufacturers are becoming increasingly concerned about the issue of sustainability. For instance, recognition of the relationship between manufacturing operations and the natural environment has become an important factor in the decision making among industrial societies.

Making development sustainable is in general a challenging and complex undertaking, involving such factors as technology and engineering, economics, environmental stewardship, health and welfare of people and the communities in which they live and work, social desires, and government strategies, procedures and policies. More specifically, making manufacturing sustainable requires balancing and integrating economic and environmental societal objectives, supportive policies and practices. Appropriate trade-offs are often necessary, given the diverse interests of manufacturers and society. Furthermore, relevant, meaningful, consistent and robust information on sustainable manufacturing must be available and utilized by organizations and their managers if sustainability is to improve in manufacturing.

This article describes sustainable manufacturing and the role of environmental sustainability in achieving it. This includes consideration of relevant environmental issues, green manufacturing, life cycle factors, and priorities in advancing manufacturing operations and processes. A case study is presented in which environmental sustainability is considered holistically in decision making for a manufacturing operation. The objective is to improve understanding and to foster advances in sustainable manufacturing. This objective is particularly important since increased research, information, and technology transfer is needed if sustainable manufacturing is to become adopted quickly and in a widespread manner in the future.

2. Background: Sustainability and Sustainability Indicators

In describing, understanding and applying sustainable manufacturing, it is important to have knowledge of sustainability and indicators for it. These topics are explained in this section.

Sustainability is a concept that has been defined in many ways and has different meanings to different people. Sustainable development was introduced in a widespread way by the Brundtland Commission, which defined it as development that “meets the needs of the present without compromising the ability of future generations to meet their own needs” [1].

At its core, sustainability is simply the ability to endure or survive, which has significant ramifications. For instance, sustainability describes the productivity and diversity over time of biological systems, from an ecological perspective, and the potential for long-term welfare, from a human perspective. The latter depends on the wellbeing of the natural world, including the responsible use of natural resources and disposal of wastes. Sustainability involves stabilizing the currently disruptive relationship between humanity and our planet [2]. Such an effort is challenging, as the human system and the planetary system are both very complex.

In the context of human development and environmental stewardship, the term sustainability has ideological, political, ecological and economic contexts [3] and, in this framework, it is most commonly seen as a derivation of the term sustainable development [4]. Sustainability can be viewed as having three parts: environmental, economic and social (including political) (see Figure 1). As a consequence, achieving sustainability requires an integrated approach and multi-dimensional indicators that link a community’s economy, environment and society.

Figure 1. Sustainability as the intersection of its three key parts, and examples of features at the intersection of any two parts.

An important facet of measuring and assessing sustainability and efforts to enhance it are sustainability indicators. Indicators help identify the status of something, the progress made towards an objective, and the challenges and problems in moving towards an objective as well as the measures that must be adopted to address the challenges and problems. Indicators of sustainability are different from traditional indicators of economic, social and environmental progress. Indicators for a sustainable community identify where the links between economics, environmental stewardship and society are inadequate, and suggest and prioritize approaches to address the problems. Traditional indicators, like economic profitability, health and water quality, measure changes in one part of a community independent of the other parts, whereas sustainability indicators reflect the relations among the three aspects of sustainability and the many factors that affect them. Figure 2 illustrates the relations, showing, for example, that:

• the natural resource base provides the materials for production on which jobs and profits depend;
• employment affects wealth creation, living standards and poverty rates;
• poverty relates to crime and social unrest and instability;
• resource, air and water quality affect health; and
• resources used for production affect profits.

For instance, health problems affect worker productivity and health insurance costs, and poor water quality prior to use in a process that requires clean water necessitates the extra expense and reduced profits associated with water treatment. Many traditional indicators are not holistic, like gross domestic product (GDP), which measures the amount of money being spent in a country. GDP is generally regarded as a measure of a country's economic well-being, under the presumption that the more money spent, the higher the GDP and the better the economic well-being, although this indicator reflects only the amount of economic activity, regardless of how that activity affects the community social and environmental welfare.

Effective indicators for sustainability and other purposes share several common characteristics: (1) relevance, in that they reveal necessary information about a system or process; (2) understandability, in that they are straightforward and readily understood by experts and non-experts; (3) reliability, in that they provide information that is trustworthy; and (4) assessable, in that they are based on available and accessible data.

Figure 2. Relations between social, environmental and economic parts of sustainability, and some of the factors that comprise them.

3. Sustainable Manufacturing

The link between manufacturing and its operations to the natural environment is gradually becoming recognized. Progress, profitability, productivity and environmental stewardship are now seen as needing consideration by manufacturing organizations [5]. Improving environmental stewardship and sustainability, while maintaining profitability and productivity, are increasingly viewed as strategic goals of manufacturing companies.

3.1. Manufacturing and the Environment

Traditionally strategies for manufacturing have considered production process comparisons for the volume/variety matrix of the products [6]. Today, manufacturing strategies generally account for products and processes, as well as other parameters like practices, so as to incorporate organizational and philosophical elements of manufacturing strategy. This yields more general viewpoint. A technological dimension is included, since manufacturing is heavily technologically driven.

Manufacturing operations and the natural environment are becoming increasingly linked. To incorporate a measure of environmental impact in manufacturing strategies, expressions for assessing the environmental impact (EI) on society can be used. One common expression for the environmental impact on society is EI = P × A × T, where P, A and T denote population, affluence and technology respectively [7,8,9]. Population is difficult to constrain and affluence is increasingly sought by people. Thus, technology, which can be defined as the knowledge of an organization [10], is the factor that can be improved to reduce environmental impact. The technology category relating to the environment and manufacturing is affected by the following three factors:

• Product: The manufacturing strategy for environmentally benign products often involves a design process which accounts for environmental impacts over the life of the product. Consequently it is normally associated with the use of design for environment (DFE) and life cycle analysis (LCA) methods. Designing products to be environmentally benign can contribute to their successful introduction and maintenance. Product flexibility, for example, allows for environmental improvements, like materials substitution, while retaining competitiveness. The expected decrease in product life cycles with increased product customization is likely to make flexibility increasingly important.
• Process: Environmental improvements related to manufacturing processes are linked to reduction, reuse, recycling and remanufacturing. Zero-emission (i.e., closed-loop) manufacturing views the manufacturing system as an industrial ecosystem, and requires the reuse of wastes or by-products within the manufacturing system. Thus, zero-emission manufacturing requires capabilities for pollution prevention (e.g., substitution) and waste reuse. Flexible manufacturing also requires the capability for material flexibility, and manufacturing equipment that can accommodate variations in material flows can assist in enhancing sustainability while maintaining competitiveness. For instance, more efficient and recyclable packaging designs can make packaging more sustainable.
• Practices: An important environmentally-based influence on organizational manufacturing practices is ISO 14000 certification, which can support organizational practices but does not make environmental improvements a certainty on its own [5]. Practices can be used strategically to improve manufacturing, through such other activities as benchmarking and performance measurement, since such schemes assist managers in developing and maintaining new environmental programs and technology.

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Rapid 3D prototyping is an additive manufacturing process involving creating three-dimensional objects from digital files. In this process, a fabricator creates objects by laying down successive material layers. Each layer is a thin-sliced cross-section of the final object.

Unlike the traditional subtractive manufacturing process, 3D printing does not involve cutting out pieces of the material. Furthermore, it enables the production of complex shapes with lesser materials. There are three major types of 3D printing, depending on the accuracy levels required. They include the following:

• Fused Deposition Modeling (FDM). This 3D printing prototyping technique is the most popular and cost-effective option available. It is easy to use and involves thermoplastic filaments with layer-by-layer extrusion. This process is growing rapidly, and it is suitable for product development.
• Selective Laser Sintering (SLS). This is a 3D printing technique used for both plastic and metal prototyping. It uses powder beds to build prototypes layer after layer, using a laser for heating and sintering the powdered material.
• Stereolithography (SLA). This method creates a 3D prototyping with a tank of photosensitive liquid resins. Ultraviolet (UV) light then helps solidify each layer of the product. This process continues until the model is complete. It is a recommended solution for high-resolution 3D prototypes.

Rapid prototyping 3D printers are valuable for making products ranging from mechanical parts and architectural models to jewelry designs and other consumer products.

Advantages of Rapid 3D Prototyping

Several industries worldwide are embracing the 3d prototype printing technique due to its several vital advantages over the traditional manufacturing techniques. These advantages include:

Design Flexibility

3D printing enables you to create various iterations of your designs effectively. It gives you more design freedom and flexibility than several other manufacturing techniques. A 3D prototype is created using 3D modeling software. Therefore, the process allows you to easily create your designs, regardless of how simple or intricate they are. It also gives you room to make any prototype from scratch while adjusting your 3D model at any point in the production stage. This helps save headaches while using 3D printing for mass production.

Furthermore, any given 3D printer can print almost any product, provided it fits within its build volume. Moreover, the convenience of rapid prototyping 3D printing makes it a great choice for every project. Since you need to make several changes to get the desired final product, you won’t have to create a new mold for every iteration of your project. There is little or no change in the equipment or machinery throughout the process.

Unlike traditional techniques, 3D printing allows you to include multiple materials into one object. Thus, you have an array of matched mechanical properties, colors, and textures. You’ll also be able to create and manufacture geometries that are impossible for traditional manufacturing methods. Such geometries include parts within parts and hollow cavities in solid parts. You can edit your designs however you like to create unique, quality parts.

Money Saving

3D prototyping is relatively cheaper than other manufacturing methods like injection molding. As we mentioned earlier, you won’t have to create new molds each time you change your design. This is a significant advantage, particularly for small production runs. The 3D printing process requires only one or two machines with few operators to create a component.

There is usually no need for additional tooling in this process. Thus, 3D printing service cost is usually minimal. In addition, material waste in 3D printing is very low because it is an additive manufacturing process. It involves building a component from the ground up, and there is no carving out of solid blocks as with CNC machining.

Time Saving

One of the most significant advantages of 3D printing technology is that it ensures rapid prototyping. As a result, you can design, develop, and test your custom part in the shortest time possible. Even if you have to modify the design at any point, you can do it without necessarily affecting the manufacturing speed. Unlike the traditional processes, 3D printing techniques allow you to design your part, manufacture it in-house, and test it within a few days or less.

Additive manufacturing also skips the process of creating mold and waiting for tool preparation. This is often a significant difference for small businesses requiring small production runs. You can accelerate product development and get products to market in short lead times. You are also free from the issue of minimum orders.

Functional Prototype Testing

The wide range of 3D printing materials available today makes it possible to create advanced functional prototypes. These prototypes are the ones you deploy for cost-effective market testing to ensure that they meet your requirements and the needs of your consumers.

You can easily test a 3D printing prototype and modify the CAD file if you discover any flaws. You get feedback from your potential investors and customers on the physical product without risking large upfront prototyping expenditures. This gives you an overall competitive advantage in your industry.

How to 3D Print Prototypes

The prototype 3D printing process occurs in four essential stages, and they are:

CAD Design

The starting point of your 3D prototyping project is the development of a CAD design file. You can work with product design firms to develop the 3D software for the extrapolation of the design. There are several file formats available for 3D printing. It is crucial that you first check the file formats supported by the printer.

Furthermore, you should check for the available programs for designing the files. Some of the common file formats available are:

• STL
• OBJ
• AMF
• 3MF

Once there is a printable file, you can then go ahead to prepare the file for your 3D printer. Hence, the next stage.

Digital Pre-Processing

The process of preparing your file for your printer is called slicing. This means that you’re dividing the 3D model into hundreds of layers using slicing software. Once sliced, your file is ready for the printer, and you can feed it in via USB, Wi-Fi, or SD.

The digital pre-processing stage also involves the choice of materials and parameters. There are several 3D printing materials to choose from based on the desired properties of your final product. Also, you need to define other parameters of the process, including placement and size of the print.

3D Printing Your Prototype

Once you upload the sliced file into the 3D printer, the printing process begins. 3D printers use instructions in the file to dictate the material disposition. The printers then build the part by depositing layers of the 3D printing material. Although they have similar principles, the type of printer you use will determine how the process will be completed. There may also be post-processing finishes like painting and powder brushing after the printing process.

Inspection

Once your 3D prototyping is complete, the next step is to inspect the prototype and take it for market testing. This is usually the case for functional prototypes. In-house engineers can inspect the component for flaws and changes. You can also take it out to potential consumers to ensure it meets their needs. If there is a need for changes, there is enough room for it.

RapidDirect’s 3D Printing Services

Completing your 3D printing project is always easier when you work with the best prototyping partner. RapidDirect offers you a high-quality and cost-effective 3D printing service that will meet the unique requirements of your project. Our in-house printing factory and technical capabilities cover major 3D printing methods, including FDM, SLS, SLA, and Polyjet. Furthermore, we offer you an extensive array of materials and post-processing options.

When you upload your CAD files and specify your requirements, our quoting platform generates rapid quotations within two hours. Our abundant manufacturing resources also allow us to offer cost-effective pricing for your project. More importantly, RapidDirect provides fast lead times as fast as three days to allow you to get your product to market in a short time. Upload your design file today!

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When the concept of anesthesia for surgery was first introduced half a century ago, only one cardiograph was available at the operating theater, and we were checking for signs of crisis using this device in combination with visual inspection, palpation, percussion, auscultation, intermittent manual measurement of the blood pressure, and also clinical intuition. After pulse oximetry was introduced, it became possible to evaluate the status of oxygenation, ventilation, circulation, body temperature and muscle relaxation using scientific indicators, on the basis of the principle of vigilance. For example, it became possible to detect imminent cardiac arrest about 1 min before its occurrence if arterial blood oxygen saturation (SpO₂) monitoring was performed, and several min before its occurrence if end-tidal carbon dioxide (ETCO₂) monitoring was performed, whereas the time from the detection of signs of cardiac arrest to the occurrence of cardiac arrest was only 10 s when ECG monitoring was performed.

Background

For us anesthesiologists whose mission is to protect the life of patients under conditions of body invasion, in which there may be only s/min left until the onset of a critical condition, introduction of the pulse oximeter enabling non-invasive measurement of SpO₂ was a great relief, as if we had met Buddha in hell. This was a brilliant achievement which later triggered advances in the monitoring of vital signs as well. Discovery by Dr. Takuo Aoyagi, in 1974, of the principle of measurement of the arterial oxygen saturation using cardiac pulsations by pulse oximetry has contributed greatly to mankind. At first, an ear oximeter was manufactured on a trial basis for clinical application of this principle, but the device was not commercialized, and research for its commercialization suffered a setback and delay.

Nearly, 10 years later, pulse oximeters with fingertip sensors were developed in the US, followed by the rapid spread of these devices. Japan hastily introduced the devices made in the US without laying claim to the fact that the pulse oximeter principle was first invented in Japan (by Dr. Aoyagi), until Prof. Severinghaus (University of California, San Francisco) publicized the fact in 1986.

I was shocked when I was informed by Prof. Michiaki Yamakage (Chief Secretary, Japan Association for Clinical Monitoring) of the death of Dr. Takuo Aoyagi on April 18, 2020. At that time, my memory of him ran like a revolving lantern, including my seeing Dr. Aoyagi, while he was alive, and events related to him during the days when I was involved in spreading the clinical application of pulse oximeters. On this occasion, I would like to present some of those scenes in memory of Dr. Aoyagi while dedicating my deep respect and gratitude to him.

Operating room safety management committee

It was in 1976 that the Operating Room Safety Management Committee was constituted within the Japanese Society of Anesthesiologists (JSA). Prof. Hideo Yamamura (University of Tokyo) served as the first chairman of this committee. Later, the role of the chairman was passed on to Professors Toyohisa Arai, Keizo Takahashi, Ken’ichi Kobayashi and Masahiro Suzuki in that order, and the baton was also handed at one time to the author. In those days, anesthesia was viewed unfavorably by people, and there prevailed a negative attitude about anesthesia itself being a risk factor for operation. For example, when the patient died as a result of a poor operative outcome, explanation like the following was often offered without hesitation: “The operative procedure itself was successful, but the patient failed to wake up from anesthesia,” etc.

On the 31^st Conference of the JSA in 1984, a symposium titled “Towards Safer Anesthesia” was organized. This was the first meeting focusing on the safety of anesthesia in the setting of an academic conference. Around that time, I began to place great importance to the activities within the framework of the Operating Room Safety Management Committee, which eventually led to the publication of “Guidance on Monitoring for Safe Anesthesia” on April 21, 1993. The process until preparation of this guidance is described in the published monograph “Guidebook—Guidance on Monitoring for Safe Anesthesia by the JSA” (edited by Masahiro Suzuki and Toyohisa Arai, published by Kokuseido Co., Ltd., 1995). This guidance has been revised four times and provides easily understandable guidance while avoiding ambiguous expressions.

A survey of accident cases related to anesthesia was conducted in parallel with the creation of this guidance. At some point of time, some of the survey staff proposed that the survey be discontinued, because data collection and entry were labor-intensive. However, our definitive determination to continue with the survey was understood by successive members of the committee and the staff in charge of the survey at each leader hospital, so that the survey has been continued to date, without interruption. Analysis of the data collected during this survey has yielded significant outcomes, such as the creation of the guidance for countermeasures against massive bleeding and guidance for prevention of pulmonary embolism.

Why was the guidance created so rapidly?

Development of a concrete guidance was started at a time when standards on intraoperative monitoring were being published one after another in European countries, modeled after the standard published in 1986 by the American Society of Anesthesiologists (ASA). Needless to say, the introduction of pulse oximetry served as a driving force for these actions.

Another factor which prompted rapid creation of the guidance was the death of two patients caused by accidental erroneous inhalation of pure nitrous oxide at an influential national hospital in Kyushu in 1987. The episode was attributed to an error in the arrangement of the supply pipes for oxygen and nitrous oxide made during the construction of the hospital. Although the anesthesiologists involved in the care of the victims were exempted from legal responsibility, a tense atmosphere prevailed in those days at the mention of anesthesia, and we resolved to never have such accidents recur.

Preparation for wiping out the demon: Monitored Anesthesia Care (MAC)

In recent years, it has become mandatory for the guidance on monitoring to be followed if a test or treatment requiring anesthesia is undertaken even outside the operating room. Introduction of such a regulation is also being debated now in Japan, under the so-called MAC. If anesthesia provided without the MAC results in an adverse event, the healthcare provider concerned will be judged as “having been negligent, i.e., there is a default obligation on experts to predict the possible risks associated with a given medical act and to take steps to avoid the risks.” Simply said, invasive medical acts under environments that lack preparation for risk management are unacceptable. MAC is “a preparatory step for wiping out the demon” hidden behind medical acts. In Japan, however, reimbursement for MAC is not provided by the national health insurance system to the physicians in charge of vigilance, putting a considerably heavy burden on the healthcare providers.

Japan association for clinical monitoring

When talking about Dr. Aoyagi, I cannot omit to referring to the Japan Association for Clinical Monitoring founded under the initiative of Prof. Akira Okuaki (Fukushima Prefectural Medical University). At the meetings of this association, Dr. Aoyagi often presented research data aimed at improving the precision of pulse oximeters and optimizing the cost of this device. He also made a presentation at the 7th conference of this association held in Fukuoka and was awarded the Okuaki Memorial Prize in the following year. In those days, Prof. Katsuyuki Miyasaka (National Children’s Hospital) was also actively involved as a co-researcher in the research conducted by Dr. Aoyagi. Prof. Okuaki invited researchers from varied specialties to this association to allow multidisciplinary wisdoms to debate an issue, and Dr. Aoyagi was a very valuable asset for this association. It was also impressive that Prof. Kunio Suwa (University of Tokyo), who was the best speaker on oxygen-related topics among Japanese researchers, enthusiastically suggested that the performance of Dr. Aoyagi was worthy of a Nobel Prize.

Talk of Nobel Prize

Awarded to the research on hypoxia-inducible factor (HIF)

The year 2001 was the 100th anniversary of awards of the Nobel Prize. In those days, Prof. Lindahl (Department of Anesthesiology, Karolinska Institute) was the chairman of the Nobel Committee for Physiology or Medicine. I became acquainted with him in those days, and we became reasonably good friends as we were around the same age (born in 1943). Prof. Lindahl always talked passionately about the beauty and novelty of science.

We asked him to deliver a special speech at the 49th Conference of the Japanese Society of Anesthesiologists in 2002. We asked him to refer to the (1) criteria for selection of a Nobel Prize winner and (2) introduction of the research in our field that would be the worthiest of this prize, when delivering the special speech. He immediately responded to this request, saying that the answer to (1) was “good for mankind”, i.e., great contribution to mankind, and to (2) was the research on biological reactions to hypoxia from the standpoint of molecular genetics. On that day at the Conference, his audience was fascinated by his smart and appealing special speech.

The Nobel Prize in Physiology or Medicine 2019 was awarded to 3 researchers, including Prof. Semenza (Johns Hopkins University), for their contribution to elucidation of the mechanism of cellular sensing and responses related to oxygen utilization. We were excited much by the Nobel Prize having been awarded for a field of research that was of interest to us. According to the special article by Prof. Kiichi Hirota (Kansai Medical University), published in the November issue of LiSA, 2019 in Japanese, these 3 researchers were awarded the prize for their detection and isolation of HIF as a factor, a component of the molecular mechanism involved in the induction and maintenance of erythropoietin expression, as well as elucidation of the molecular mechanism for oxygen tension-dependent HIF activity modulation. I hear that Prof. Hirota was involved in isolating the gene encoding the HIF molecule as a member of the laboratory led by Prof. Semenza.

Very broadly speaking perhaps, the connection between SpO₂ and HIF can be viewed as a dialogue between oxygen and the living body during the course of external and internal respiration closely involved in homeostasis and evolution.

Criteria for award of the Nobel Prize

During the 75 years after World War II, slightly more than 25 Japanese have been awarded the Nobel Prize. Why was Dr. Aoyagi not awarded the Nobel Prize? Prof. Kunio Suwa had pointed out on several occasions that Dr. Aoyagi deserved this prize, and Prof. Katsuyuki Miyasaka had also provided strong support for the awarding of this prize to Dr. Aoyagi. I also tried to use the best of my limited abilities for this purpose, advising Prof. Lindahl (Chairman of the Nobel Committee) that the performance of Dr. Aoyagi satisfied the criterion “good for mankind” for award of the Nobel Prize. At that time, I thought the chairman subtly told me that while his work was great, it was still some distance from deserving the Nobel Prize. However, because of my poor language abilities, I am not confident that I understood his response completely. He did seem, though, to suggest the weak points of Dr. Aoyagi, i.e., the fact that his first paper was written in Japanese and that the intellectual proprietorship of the outcome of his research had not been established by a globally valid method. It has been pointed out for many years that the basis for the protection of intellectual proprietorship is weak in Japan and that Japanese enterprises show poor capability for translating advanced technologies. I think that these shortcomings remain open issues even until date.

Despite such limitations, the greatness of Dr. Aoyagi’s performance has been steadily enriched. His research has led to submission of many applications for patent registration (linked to US patent registration), publication of papers in journals, such as Anesthesiology and Anesth Analg, and awards of many professional society prizes, such as the Patent Agency Director’s Encouraging Prize, the Science and Technology Director Award, the Medal with Purple Ribbon, Gravenstein Lifetime Achievement Award of the Society for Technology in Anesthesia (USA), the Institute of Electrical and Electronic Engineers (IEEE) Medal For Innovations In Healthcare Technology, and so on. Thus, global recognition of the performance of Dr. Aoyagi has been deepening. Although not satisfying the criteria for the Nobel Prize, the intellectual relics left by Dr. Aoyagi will remain brilliant forever.