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

一种市售的光电反射器（Hamamatu Photonics，型号P2826），它结合了发光二极管（LED）和光电晶体管（Ptr），已被用于光电容积计。该设备在一个芯片内成型（4*4*2mm），价格便宜，体积小巧，易于应用于皮肤表面的所有区域。相对于一般使用的钨丝灯的广谱波长，LED在红外范围内的光谱分布较窄，适合于皮肤组织的光度测量，不受可见光的干扰影响。Ptr输出的光谱分布与LED的光谱分布有很大的重叠。由于LED发出的是冷光，不存在光源发热引起局部血管舒缩反射变化的问题。另一方面，Ptr相对不受温度和先前光历史的影响。这些特点表明，光反射体体积脉搏描记仪优于体积庞大的微型钨丝灯光导电池组合。我们已经在心理生理学实验（即自然睡眠实验）中测试了这些新的体积脉搏仪的长期稳定性，并将其应用于精神病患者的临床测试。在测量过程中，受试者不会感到不适或局部发热，并且还获得了无伪影的数据。光反射式容积脉搏描记器似乎满足定量光容积脉搏描记所必需的换能器标准。

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.