Source–Detector Spectral Pairing-Related Inaccuracies in Pulse Oximetry: Evaluation of the Wavelength Shift

Abstract

Pulse oximetry enables oxygen saturation estimation ( S p O 2) non-invasively in real time with few components and modest processing power. With the advent of affordable development kits dedicated to the monitoring of biosignals, capabilities once reserved to hospitals and high-end research laboratories are becoming accessible for rapid prototyping. While one may think that medical-grade equipment differs greatly in quality, surprisingly, we found that the performance requirements are not widely different from available consumer-grade components, especially regarding the photodetection module in pulse oximetry. This study investigates how the use of candidate light sources and photodetectors for the development of a custom S p O 2 monitoring system can lead to inaccuracies when using the standard computational model for oxygen saturation without calibration. Following the optical characterization of selected light sources, we compare the extracted parameters to the key features in their respective datasheet. We then quantify the wavelength shift caused by spectral pairing of light sources in association with photodetectors. Finally, using the widely used approximation, we report the resulting absolute error in S p O 2 estimation and show that it can lead up to 8% of the critical 90–100% saturation window.

Multi-domain Modeling and Simulation of an Oximeter: PVT Variations Impact of Opto-electronic Devices on the SpO2 Quantification

“…Then, the P_R and P_IR subblocks are used to convert the output current i R of LHQ974o and SFH4080o into luminous intensity in Watt. The actual spectral distribution of both LEDs is usually modeled by a Gaussian curve (Tsiakaka, et al, 2020) and the total radiant flux is the integral of the entire spectrum.…”

“…The second step is to validate the whole system by comparing our simulation data with previous results (Tsiakaka, et al, 2020), where authors used six different pairs of red/IR LED to plot six SpO 2 -R OS curves. We were able to measure these LEDs optical and electrical characteristics, in order to simulate these devices with our developed model.…”

“…For the PD, a model of the BP104S was used. As for the biological medium, we applied the same finger Figure 6: a) Simulation result with our models for the six different red/IR LED pairs; b) SpO 2 deviation curves between our works and (Tsiakaka, et al, 2020). model.…”

“…It shows the "110-25R OS " curve, as it is a widely used reference to basically estimate SpO 2 . We then compared our simulations to Figure 9.b in (Tsiakaka, et al, 2020), with the only difference being the used PD (BP104S for us and FDS100 for the previous work). Figure 6.b shows the SpO 2 deviation curves between our models and the previous results, for all six red/IR LED pairs.…”

Continuous monitoring of Physiological parameters using PPG

“…Because of the advancement of technology and research, such as spectrophotometry, opt acoustic and transmission spectroscopy, many low-cost and simple non-invasive technologies have emerged. Several researchers had discussed the uses of multi-wavelength pulse oximeters to detect hemoglobin levels, and SpO 2 (29)(30)(31)(32) . Macknet et al evaluated Hb measurement with hemodilution and compared it with pulse CO-Oximeters and invasive laboratory CO-Oximeter Hb measurements which were carried out in both healthy and surgical subjects (33) .…”