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

Task 1

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. 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.

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.

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

Task 2

Every system and organ in the body needs oxygen to survive. Without oxygen, cells begin to malfunction and eventually die. Cell death can cause severe symptoms and ultimately lead to organ failure. The body transports oxygen to the organs by filtering it through the lungs. The lungs then distribute oxygen into the blood via hemoglobin proteins in red blood cells. These proteins provide oxygen to the rest of the body. Pulse oximetry measures the percentage of oxygen in hemoglobin proteins, called oxygen saturation. Oxygen saturation usually indicates how much oxygen is getting to the organs.

Some factors can reduce the accuracy of a pulse oximeter reading, including:

• changes in the pulse
• carbon monoxide poisoning which may not produce an alert in a pulse oximeter
• bilirubin levels
• lipids in blood plasma
• interference from external light or color, including nail polish
• having cold hands or poor circulation

Finger pulse oximeters are medical devices. Individuals should therefore avoid any devices that lack FDA approval, because they may not be accurate or work consistently. Other considerations include cost, warranty and extra features, such as pulse readings.

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. 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.

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 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.

Task3

A pulse signal such as photoplethysmograph (PPG) can be captured by using Programmable System-on-Chip (PSoC) platform for pulse oximeter application. The Pulse Oximeter is used to measure oxygen saturation in a blood and monitor heart rate by using SpO2 Sensor, a transmission type PPG sensor. The Pulse Oximeter system consists of SpO2 sensor, signal generator, amplifier, filter, ADC, SpO2 and Pulse rate detection module and LCD. Figure named Block diagram of Pulse Oximeter illustrates the block diagram of the proposed Pulse Oximeter system. The amplifier converts the current signal from the sensor to voltage, while the filter limits the signal into certain frequency. The
system uses a 13-bit resolution ADC. The SpO2 and pulse rate detection module uses peak finding algorithm and displays the detection result on a LCD.

The pulse oximeter is developed to measure patient pulse oximetry data. The pulse oximeter architecture is shown in Figure named Architecture of pulse oximeter.
(i) SpO2 Sensor: This measures SpO2 and pulse rate using an infrared LED, a red LED, and a light sensor
photo (PIN) diode. Infrared light and red light are passed through the user’s finger the PIN diode.
(ii) Amplifier: This amplifies the input signal.
(iii) Analog Filter: This decoupled the high-frequency noise.
(iv) ADC. This converts a continuous signal to discrete signal.

Task 4

FMEA of pulse oximeter is attached below.

Task 5

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. 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. 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 HR PPG and SpO₂ measurement.

References

https://www.grandviewresearch.com/industry-analysis/pulse-oximeter-market

analog.com/en/technical-articles/how-to-design-a-better-pulse-oximeter.html

https://www.medicalnewstoday.com/articles/finger-pulse-oximeter#what-to-look-for

https://www.researchgate.net/publication/312325893_A_study_on_real-time_pulse_sensor_interface_with_system-on-chip_architecture/link/5acb0c01a6fdcc8bfc84f7ac/download

https://www.researchgate.net/publication/292205525_Design_of_a_finger_base-type_pulse_oximeter

https://www.researchgate.net/publication/281195648_A_Prototype_of_Reflection_Pulse_Oximeter_Designed_for_Mobile_Healthcare

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC137227/

https://www.nxp.com/docs/en/application-note/AN4327.pdf