Department of Electrical and Computer Engineering, Newark College of Engineering, New Jersey Institute of Technology, New Jersey, 07102, USA.
Department of Electrical and Computer Engineering, Drexel University, Philadelphia, PA, 19104, USA.
J Clin Monit Comput. 2021 Aug;35(4):797-813. doi: 10.1007/s10877-020-00539-2. Epub 2020 Jun 17.
Calculation of peripheral capillary oxygen saturation [Formula: see text] levels in humans is often made with a pulse oximeter, using photoplethysmography (PPG) waveforms. However, measurements of PPG waveforms are susceptible to motion noise due to subject and sensor movements. In this study, we compare two [Formula: see text]-level calculation techniques, and measure the effect of pre-filtering by a heart-rate tuned comb peak filter on their performance. These techniques are: (1) "Red over Infrared," calculating the ratios of AC and DC components of the red and infrared PPG signals,[Formula: see text], followed by the use of a calibration curve to determine the [Formula: see text] level Webster (in: Design of pulse oximeters, CRC Press, Boca Raton, 1997); and (2) a motion-resistant algorithm which uses the Discrete Saturation Transform (DST) (Goldman in J Clin Monit Comput 16:475-83, 2000). The DST algorithm isolates individual "saturation components" in the optical pathway, which allows separation of components corresponding to the [Formula: see text] level from components corresponding to noise and interference, including motion artifacts. The comparison we provide here (employing the two techniques with and without pre-filtering) addresses two aspects: (1) accuracy of the [Formula: see text] calculations; and (2) computational complexity. We used both synthetic data and experimental data collected from human subjects. The human subjects were tested at rest and while exercising; while exercising, their measurements were subject to the impacts of motion. Our main conclusion is that if an uninterrupted high-quality heart rate measurement is available, then the "Red over Infrared" approach preceded by a heart-rate tuned comb filter provides the preferred trade-off between [Formula: see text]-level accuracy and computational complexity. A modest improvement in [Formula: see text] estimate accuracy at very low SNR environments may be achieved by switching to the pre-filtered DST-based algorithm (up to 6% improvement in [Formula: see text] level accuracy at -10 dB over unfiltered DST algorithm and the filtered "Red over Infrared" approach). However, this improvement comes at a significant computational cost.
计算人体外周毛细血管血氧饱和度[公式：见正文]水平通常使用脉搏血氧仪，利用光体积描记法（PPG）波形。然而，由于受试者和传感器的运动，PPG 波形的测量易受运动噪声的影响。在这项研究中，我们比较了两种[公式：见正文]级计算技术，并测量了使用心率调谐梳状峰滤波器进行预滤波对其性能的影响。这些技术是：（1）“红光比红外光”，计算红光和红外 PPG 信号的交流和直流分量的比值[公式：见正文]，然后使用校准曲线确定[公式：见正文]水平 Webster（in：Design of pulse oximeters，CRC Press，Boca Raton，1997）；（2）一种抗运动算法，使用离散饱和度变换（DST）（Goldman in J Clin Monit Comput 16:475-83, 2000）。DST 算法在光路上分离出单个“饱和度分量”，从而可以将与[公式：见正文]水平对应的分量与对应于噪声和干扰（包括运动伪影）的分量分离。我们在这里提供的比较（使用带和不带预滤波器的两种技术）涉及两个方面：（1）[公式：见正文]计算的准确性；（2）计算的复杂性。我们使用了合成数据和从人体受试者收集的实验数据。受试者在休息和运动时接受测试；在运动时，他们的测量受到运动的影响。我们的主要结论是，如果有不间断的高质量心率测量，则经过心率调谐梳状滤波器预处理的“红光比红外光”方法在[公式：见正文]级准确性和计算复杂性之间提供了首选的折衷方案。在非常低的 SNR 环境下，切换到预滤波的基于 DST 的算法可以略微提高[公式：见正文]估计的准确性（与未滤波的 DST 算法相比，在-10 dB 时[公式：见正文]水平准确性提高 6%，与滤波的“红光比红外光”方法相比）。然而，这一改进是以显著的计算成本为代价的。
