光反射式脈動感測器的分析

光體積變化描記器(PPG)是一種可以簡易測量組織內血液體積變動的方法。量測訊號中包含血管收縮時的低頻訊號與脈搏跳動時的高頻訊號。由於穿透式的量測在使用上受限於只能量測光可穿透的部位。而反射式則可在大部分的體表部位上做量測，所以在使用上要比穿透式來的方便。本研究的目的是分析影響光反射訊號品質的因素。這些影響因素包含有光源至光感測器間的距離、光源的波長、光源的亮度、與皮膚組織的光學性質。在實驗中，使用四種不同波長的發光二極體(LEDs)作為光源，以光電晶體元件作為光感測器。並以微調座控制調整光源與光感測器之間的距離，調整範圍從2mm到15mm。量測食指、前臂、與額頭部位的反射式光體積變化描記訊號。要決定最佳的光源至光感測器間的距離，應該選擇低頻訊號能有較大的動態範圍，且不超過儀器偵測上限而使訊號飽和。同時具有較高的高頻灌流指數(訊號交流對直流成分的比值)條件下的感測間距。在所使用的四種光源波長中，以黃綠色(571nm)為光源，當光源與光感測器間的距離為3.2mm時，可獲得較穩定和可靠的反射式光體積變化描記訊號。

關鍵字

反射式量測；灌流指數；光體積變化描記器；訊雜比

並列摘要

Photoplethysmography is an easy method for measuring blood volume change in tissue. It's detect signals include: the vasoconstriction low frequency signal and the pulse's high frequency signal.Since the transmission type of measurement is limited to only a few specific positions that have a short pathlength.The reflectance type can be more convenient to apply on most part of body surface.This study is to analyze the factors that determine the quality of light reflectance signal. These factors include: the emitter-detector distance, wavelength, light intensity, and optical properties of skin tissue. In this study, light emitting diodes (LEDs) with four visible wavelengths were used as the light emitters, and a phototransistor was used as the light detector. A micro translation stage can adjust the emitter-detector distance from 2 mm to 15 mm. The reflective photoplethysmograph signals were measure on finger, forearm, and forehead. The optimal emitter-detector distance should be chosen to have a large dynamic range for low frequency drifting without signal saturation and a high perfusion index (AC-to-DC ratio).Among the four wavelengths, the yellowish green (571nm) light with 3.2 mm of emitter-detection distance is most suitable for obtaining a steady and reliable reflective photoplethysmograph signal.

並列關鍵字

signal-to-noise ratio ； perfusion index ； photoplethysmography (PPG) ； reflectance measurement

參考文獻

[1] Allen, John, John R. Frame, and Alan Murry, “Microvascular blood flow and skin temperature changes in the fingers following a deep inspiratory gasp,” Physiological Measurement, vol. 23, pp. 365-373, 2002.

[2] Allen, John, “Photoplethysmography and its application in clinical physiological measurement,” Physiological Measurement, vol. 28, pp. R1-R39, 2007.

[5] Futran, Neal D., and Brendan C. Stack, Christopher Holleubeak, John E. Scharf, “Green Light Photoplethysmography Monitoring of Free Flaps,” Arch Otolaryngol Head Neck Surgery, vol. 126, pp. 659-662, 2000.

[6] Kondo, Yutaka, Katsuyuki Honda, Hiroshi Odagiri, and Takeshi Ono, “Pulse-wave measuring apparatus,” United States Patent: 5766131, 1998-07-06.

[9] Mendelson, Yitzhak, and Burt D. Ochs, “Noninvasive Pulse Oximetry Utilizing Skin Reflectance Photoplethysmography,” IEEE Transactions on Biomedical Engineering, vol. 35, pp. 798-805, 1988.

國際替代計量

光反射式脈動感測器的分析

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