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Calibration of Contactless Pulse Oximetry

Verkruysse, Wim PhD; Bartula, Marek MSc; Bresch, Erik PhD; Rocque, Mukul MSc; Meftah, Mohammed BSc; Kirenko, Ihor PhD

Anesthesia & Analgesia:
doi: 10.1213/ANE.0000000000001381
Technology, Computing, and Simulation: Original Clinical Research Report
Abstract

BACKGROUND: Contactless, camera-based photoplethysmography (PPG) interrogates shallower skin layers than conventional contact probes, either transmissive or reflective. This raises questions on the calibratability of camera-based pulse oximetry.

METHODS: We made video recordings of the foreheads of 41 healthy adults at 660 and 840 nm, and remote PPG signals were extracted. Subjects were in normoxic, hypoxic, and low temperature conditions. Ratio-of-ratios were compared to reference SpO2 from 4 contact probes.

RESULTS: A calibration curve based on artifact-free data was determined for a population of 26 individuals. For an SpO2 range of approximately 83% to 100% and discarding short-term errors, a root mean square error of 1.15% was found with an upper 99% one-sided confidence limit of 1.65%. Under normoxic conditions, a decrease in ambient temperature from 23 to 7°C resulted in a calibration error of 0.1% (±1.3%, 99% confidence interval) based on measurements for 3 subjects. PPG signal strengths varied strongly among individuals from about 0.9 × 10−3 to 4.6 × 10−3 for the infrared wavelength.

CONCLUSIONS: For healthy adults, the results present strong evidence that camera-based contactless pulse oximetry is fundamentally feasible because long-term (eg, 10 minutes) error stemming from variation among individuals expressed as A*rms is significantly lower (<1.65%) than that required by the International Organization for Standardization standard (<4%) with the notion that short-term errors should be added. A first illustration of such errors has been provided with A**rms = 2.54% for 40 individuals, including 6 with dark skin. Low signal strength and subject motion present critical challenges that will have to be addressed to make camera-based pulse oximetry practically feasible.

In Brief

Published ahead of print May 31, 2016.

Author Information

From the *Standardization Research, Patient Care and Measurements, and Data Science, Philips Research, Eindhoven, The Netherlands.

Published ahead of print May 31, 2016.

Acceptance for publication March 24, 2016.

Funding: None.

The authors declare no conflicts of interest.

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Reprints will not be available from the authors.

Address correspondence to Wim Verkruysse, PhD, Standardization Research, Philips Research, HTC 36 p 0.88, Eindhoven, The Netherlands. Address e-mail to wim.verkruijsse@philips.com.

This is an open-access article distributed under the terms of the Creative Commons Attribution-Non Commercial-No Derivatives License 4.0 (CCBY-NC-ND), where it is permissible to download and share the work provided it is properly cited. The work cannot be changed in any way or used commercially.

© 2017 International Anesthesia Research Society

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