Cui W J, Ostrander L E, Lee B Y
Department of Biomedical Engineering, Rensselaer Polytechnic Institute, Troy, NY 12180.
IEEE Trans Biomed Eng. 1990 Jun;37(6):632-9. doi: 10.1109/10.55667.
Light reflectance from soft tissue has been utilized in noninvasive clinical measurement devices such as the photoplethysmograph and the reflectance pulse oximeter. Incident light on the skin travels into the underlying layers and is in part reflected back to the surface. This paper describes the reflectance of light from in vivo tissue for wavelengths in the range from 420 to 940 nm, based on photon diffusion theory and on experimental results from studies of 17 subjects. The results show a minimum reflectance and a peak sensitivity to the blood pulsations in the wavelength range from 510 to 590 nm. Skin pigmentation is seen to attenuate reflectance rather than altering the character of the modulation spectra. Based on the model introduced in this paper, the dependence of modulation spectra on mean blood fractional volume as well as wavelength is also described theoretically, and corroborated by further experimental data at 570 and 630 nm. At these latter wavelengths, the signal-to-noise ratio was calculated for the blood volume pulsation signal in the presence of physiological noise. The median for calculated ratios of reflectance modulation by blood pulsation and ratios of signal to noise between the two wavelengths were 13.1 and 7.5, respectively, for 93 sites in nine subjects. These results are seen to be consistent with the theory.
软组织的光反射已被用于无创临床测量设备，如光电容积脉搏波描记仪和反射式脉搏血氧仪。入射到皮肤上的光会穿透到下层组织，并部分反射回表面。本文基于光子扩散理论以及对17名受试者的研究实验结果，描述了体内组织在420至940纳米波长范围内的光反射情况。结果表明，在510至590纳米波长范围内，反射率最低，对血液搏动的敏感度最高。皮肤色素沉着会减弱反射率，而不会改变调制光谱的特征。基于本文介绍的模型，还从理论上描述了调制光谱对平均血液分数体积以及波长的依赖性，并通过在570和630纳米处的进一步实验数据得到了证实。在这两个波长下，计算了存在生理噪声时血容量搏动信号的信噪比。对于9名受试者的93个部位，两个波长下血液搏动引起的反射率调制比率与信噪比的计算比率中位数分别为13.1和7.5。这些结果与理论相符。
