A multipurpose LED-transistor photoplethysmograph and its application to psychological experiments

一种商用的光反射器(Hamamatu Photonics，P2826型)结合了发光二极管(LED)和光电晶体管(PTR)，已被改装用于光电体积描记器。该装置采用单芯片(4*4*2 mm)成型，价格低廉，体积小，可方便地应用于皮肤表面的所有区域。与通常使用的钨灯相比，LED在红外范围内的光谱分布较窄，因此可以在不受可见光干扰的情况下进行皮肤组织的光度测量。PTR输出的光谱分布与LED的光谱分布有很大的重叠。由于LED产生冷光，不存在由于光源产生热量而导致局部血管运动反射变化的问题。另一方面，PTR相对不受温度和先前光历史效应的影响。这些特性表明，光反射式体积测量仪优于通常用于光体积测量的体积庞大的微型钨灯-光导电池组合。我们已经在心理生理实验，即自然睡眠实验中测试了这些新的体积计的长期稳定性，并将其应用于精神疾病患者的临床测试。受试者在测量过程中没有感到不适或局部发热，也获得了无伪影的数据。光反射式体积描记器似乎满足定量光体积描记所需的传感器标准。

A commercially available phto-reflector (Hamamatu Photonics, type P2826) which combines a light-emitting diode (LED) and phototransistor (Ptr) has been adapted for use as a photoelectric plethysmograph. This device is molded in one chip (4*4*2mm), inexpensive, small compact size, and easily applied to the all area of skin surface. As compared to generally used tungsten lamp emitting a broad spectrum of wavelength, LED possesses a narrow spectral distribution in the infrared range, which makes suitable photometric measurement of skin tissue without disturbing influence of visible light. The spectral distribution of Ptr output widely overlaps with those of LED.As LED produces cool light, there is no problem of local vasomotor reflex changes due to heat generation by the light source. On the other hand, Ptr is relatively free from both temperature and prior light history effect. These characteristics suggest that the photo-reflector plethysmograph is superior to the bulky miniature tungsten lampphotoconductive cell combination generally employed in photoplethysmography. We have tested these new plethysmograph for long term stability in psychophysiological experiments, ie natural sleep experiments, and applied to clinical test for psychiatric patients. The subjects feel no discomfort or local heating from the device during measurements, and an artifact free data is also obtained. Photo-reflector plethysmograph appear to meet the transducer criteria necessary for quantitative photoplethysmography.