Angiology
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Under certain conditions laser Doppler flowmeter (LDF) signals obtained from the finger pulp may appear very similar to those obtained by use of a direct current (dc) photoplethysmograph (PPG). A combined LDF/PPG system was used in conjunction with a circumference strain gauge as an index of volume change to identify the conditions in which the correlation between these signals was good. Simultaneous LDF and dc PPG measurements were made on 10 normal volunteers by using arterial occlusion and on 7 normal subjects by using the Valsalva maneuver at different elevations of the forearm and hand with respect to the midsternum. ⋯ The dc PPG signal may be used as a means of monitoring changes in blood flow in the finger only when venous filling is low and the return remains unrestricted. Thus, in investigations using this method, the relative position of the limb with respect to the heart should always be indicated. The LDF method appears to be a reliable indicator of blood flow changes in the microcirculation irrespective of the degree of venous filling.