Fluctuation of peripheral blood flow in subjects with circulatory impairment

¹ Laboratory of Biophysics, University of Cincinnati; and Laboratory of Cardiology, Department of Medicine, Cincinnati General Hospital, Cincinnati, Ohio

Fluctuations of the capillary blood flow in the skin of the hands of cardiac patients were compared with those of normal controls. In normal subjects the peripheral blood flow undergoes spontaneous, rhythmic fluctuations of a period of 30–60 seconds, whose main function is the regulation of the body temperature. These fluctuations were recorded by means of a probe that was sensitive to the effective thermal conductivity of the skin, which is proportional to the blood flow in its capillaries. The essential elements of the probe are two wires (constantan, 0.2 mm) of 1-cm length that are in contact with the skin at a mutual distance of 0.5 cm. One of the wires is heated by alternating current. The temperature difference that therefore develops between these wires is proportional to the thermal conductivity of the skin. It is recorded by means of thermocouples in contact with the wires. It was found that the cardiac patients had, on the average, a substantially lower amplitude of fluctuations than the normal controls. It is assumed that this may be attributed to anatomical changes of the arteriolar walls, which cause increased rigidity.