Verkruysse Wim, Bartula Marek, Bresch Erik, Rocque Mukul, Meftah Mohammed, Kirenko Ihor
From the *Standardization Research, †Patient Care and Measurements, and ‡Data Science, Philips Research, Eindhoven, The Netherlands.
Anesth Analg. 2017 Jan;124(1):136-145. doi: 10.1213/ANE.0000000000001381.
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.
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.
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 to 4.6 × 10 for the infrared wavelength.
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.
基于摄像头的非接触式光电容积脉搏波描记法（PPG）检测的皮肤层比传统的透射式或反射式接触探头更浅。这就引发了关于基于摄像头的脉搏血氧饱和度测定法校准性的问题。
我们对41名健康成年人的前额进行了660纳米和840纳米波长的视频记录，并提取了远程PPG信号。受试者处于常氧、低氧和低温条件下。将比率之比与来自4个接触探头的参考SpO₂进行比较。
为26名个体的群体确定了基于无伪迹数据的校准曲线。对于大约83%至100%的SpO₂范围并剔除短期误差，发现均方根误差为1.15%，99%的单侧置信上限为1.65%。在常氧条件下，环境温度从23°C降至7°C，基于对3名受试者的测量，校准误差为0.1%（±1.3%，99%置信区间）。对于红外波长，PPG信号强度在个体之间差异很大，约为0.9×10至4.6×10。
对于健康成年人，结果提供了有力证据，表明基于摄像头的非接触式脉搏血氧饱和度测定法从根本上是可行的，因为个体间差异导致的长期（例如10分钟）误差以A*均方根表示显著低于国际标准化组织标准要求的误差（<4%），前提是应加上短期误差。已给出了40名个体的此类误差的第一个示例，A**均方根为2.54%，其中包括6名肤色较深的个体。低信号强度和受试者运动带来了关键挑战，要使基于摄像头的脉搏血氧饱和度测定法切实可行，这些挑战必须得到解决。
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