Abstract
A photoelctric device is described which permits contact-free recording of the diameter of an in situ exposed artery. The light emitted by the filament of a bulb (6 W) is collimated by a projection lens (1:2.8, 50 mm) and directed onto the surface of a silicone photocell (12.6X6.2 mm) covered by a neutral light filter. The voltage drop caused by the photocell current flowing through an adjustable load resistor represents the signal voltage which is fed into the input of an instrumentation amplifer. The artery under investigation is positioned above the photocell parallel to its short axis. The signal voltage decreases linearly with increasing area of the shadow cast by the artery on the photocell and thus the output voltage of the amplifier is linearly proportional to the diameter of the artery. The combined frequency response of photocell and amplifier was examined by sinusoidally modulated light emitted by a luminescent diode. The amplitude ratio was constant up to 200 Hz and the time lag was about 0.2 ms. The device was used on the canine carotid and femoral arteries. An example is shown.
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