Abay T Y, Kyriacou P A
School of Mathematics, Computer Sciences and Engineering, City, University of London, London, UK.
J Clin Monit Comput. 2018 Jun;32(3):447-455. doi: 10.1007/s10877-017-0030-2. Epub 2017 May 25.
Photoplethysmography (PPG) is an optical technique that measures blood volume variations. The main application of dual-wavelength PPG is pulse oximetry, in which the arterial oxygen saturation (SpO[Formula: see text]) is calculated noninvasively. However, the PPG waveform contains other significant physiological information that can be used in conjunction to SpO[Formula: see text] for the assessment of oxygenation and blood volumes changes. This paper investigates the use of near infrared spectroscopy (NIRS) processing techniques for extracting relative concentration changes of oxygenated ([Formula: see text]HbO[Formula: see text]), reduced ([Formula: see text]HHb) and total haemoglobin ([Formula: see text]tHb) from dual-wavelength PPG signals during intermittent pressure-increasing vascular occlusions. A reflectance PPG sensor was attached on the left forearm of nineteen (n = 19) volunteers, along with a reference NIRS sensor positioned on the same forearm, above the left brachioradialis. The investigation protocol consisted of seven intermittent and pressure-increasing vascular occlusions. Relative changes in haemoglobin concentrations were obtained by applying the modified Beer-Lambert law to PPG signals, while oxygenation changes were estimated by the difference between red and infrared attenuations of DC PPGs (A[Formula: see text] = [Formula: see text]A[Formula: see text] - [Formula: see text]A[Formula: see text]) and by the conventional SpO[Formula: see text]. The [Formula: see text]HbO[Formula: see text], [Formula: see text]HHb, [Formula: see text]tHb from the PPG signals indicated significant changes in perfusion induced by either partial and complete occlusions (p < 0.05). The trends in the variables extracted from PPG showed good correlation with the same parameters measured by the reference NIRS monitor. Bland and Altman analysis of agreement between PPG and NIRS showed underestimation of the magnitude of changes by the PPG. A[Formula: see text] indicated significant changes for occlusion pressures exceeding 20 mmHg (p < 0.05) and correlation with tissue oxygenation changes measured by NIRS, while SpO[Formula: see text] had significant changes after 40 mmHg (p < 0.05). Relative changes in haemoglobin concentrations can be estimated from PPG signals and they showed a good level of accuracy in the detection of perfusion and oxygenation changes induced by different degrees of intermittent vascular occlusions. These results can open up to new applications of the PPG waveform in the detection of blood volumes and oxygenation changes.
光电容积脉搏波描记法（PPG）是一种测量血容量变化的光学技术。双波长PPG的主要应用是脉搏血氧测定法，其中可无创计算动脉血氧饱和度（SpO₂）。然而，PPG波形还包含其他重要的生理信息，可与SpO₂结合用于评估氧合和血容量变化。本文研究了在间歇性加压血管闭塞期间，使用近红外光谱（NIRS）处理技术从双波长PPG信号中提取氧合血红蛋白（HbO₂）、还原血红蛋白（HHb）和总血红蛋白（tHb）的相对浓度变化。将反射式PPG传感器贴在19名志愿者的左前臂上，同时在同一前臂的左肱桡肌上方放置一个参考NIRS传感器。研究方案包括七次间歇性加压血管闭塞。通过将修正的比尔-朗伯定律应用于PPG信号来获得血红蛋白浓度的相对变化，而氧合变化则通过直流PPG的红光和红外光衰减之差（ΔA = A₆₆₀ - A₈₅₀）以及传统的SpO₂进行估计。PPG信号中的HbO₂、HHb、tHb表明部分和完全闭塞引起的灌注有显著变化（p < 0.05）。从PPG提取的变量趋势与参考NIRS监测仪测量的相同参数显示出良好的相关性。PPG和NIRS之间的一致性布兰德-奥特曼分析表明，PPG低估了变化幅度。ΔA表明闭塞压力超过20 mmHg时存在显著变化（p < 0.05），且与NIRS测量的组织氧合变化相关，而SpO₂在40 mmHg后有显著变化（p < 0.05）。血红蛋白浓度的相对变化可从PPG信号中估计出来，并且在检测不同程度间歇性血管闭塞引起的灌注和氧合变化方面显示出良好的准确性水平。这些结果可为PPG波形在血容量和氧合变化检测中的新应用开辟道路。
