McEwen M P, Bull G P, Reynolds K J
School of Computer Science, Engineering & Mathematics, Flinders University, Adelaide, Australia.
Physiol Meas. 2009 Sep;30(9):869-83. doi: 10.1088/0967-3334/30/9/001. Epub 2009 Jul 27.
Despite its success as a clinical monitoring tool, pulse oximetry may be improved with respect to the need for empirical calibration and the reports of biases in readings associated with peripheral vasoconstriction and haemoglobin concentration. To effect this improvement, this work aims to improve the understanding of the photoplethysmography signal-as used by pulse oximeters-and investigates the effect of vessel calibre and haemoglobin concentration on pulse oximetry. The digital temperature and the transmission of a wide spectrum of light through the fingers of 57 people with known haemoglobin concentrations were measured and simulations of the transmission of that spectrum of light through finger models were performed. Ratios of pulsatile attenuations of light as used in pulse oximetry were dependent upon peripheral temperature and on blood haemoglobin concentration. In addition, both the simulation and in vivo results showed that the pulsatile attenuation of light through fingers was approximately proportional to the absorption coefficients of blood, only when the absorption coefficients were small. These findings were explained in terms of discrete blood vessels acting as barriers to light transmission through tissue. Due to the influence of discrete blood vessels on light transmission, pulse oximeter outputs tend to be dependent upon haemoglobin concentration and on the calibre of pulsing blood vessels-which are affected by vasoconstriction/vasodilation. The effects of discrete blood vessels may account for part of the difference between the Beer-Lambert pulse oximetry model and empirical calibration.
尽管脉搏血氧饱和度仪作为一种临床监测工具取得了成功，但在经验校准的必要性以及与外周血管收缩和血红蛋白浓度相关的读数偏差报告方面仍有改进空间。为实现这一改进，本研究旨在增进对脉搏血氧饱和度仪所使用的光电容积脉搏波信号的理解，并研究血管口径和血红蛋白浓度对脉搏血氧饱和度测量的影响。测量了57名已知血红蛋白浓度的人的手指的数字温度以及宽光谱光的透过情况，并对该光谱光透过手指模型的传输进行了模拟。脉搏血氧饱和度测量中所使用的光的脉动衰减比率取决于外周温度和血液血红蛋白浓度。此外，模拟和体内实验结果均表明，只有当吸收系数较小时，光透过手指的脉动衰减才大致与血液的吸收系数成正比。这些发现可根据离散血管对光透过组织的阻碍作用来解释。由于离散血管对光传输的影响，脉搏血氧饱和度仪的输出往往取决于血红蛋白浓度和搏动血管的口径，而搏动血管的口径会受到血管收缩/舒张的影响。离散血管的影响可能是比尔-朗伯脉搏血氧饱和度测量模型与经验校准之间差异的部分原因。
