Measurement of Arterial and Venous Reactivity by an Advanced Strain Gauge Plethysmograph

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Abstract
The problems of applying mercury strain gauge venous occlusion plethys mography in quantitative measurements of high blood flow rates were studied in the extremities of humans and animals. The fast-acting ECG-controlled pneumatic Periflow system opens the possibility of measurements with reduced restriction of arterial inflow. In animal experiments the arterial inflow rate (about 0.25 vol%/min) during the arterial occlusion period was estimated by an indicator dilution technique. The accuracy of the perfusion rate estimation of a limb by plethysmography was tested in controlled perfused extremities of large dogs weighing about 60 kg. Strain gauges with different positions showed dif ferent—but for each filament quite proportional—relations to real values. The nonuniform venous capacities of the different segments of a limb, which have been shown by injections of a known volume and recording of pressure volume curves, may complicate blood flow measurements by volume displacements from low-compliance regions to high-compliance regions of the vein system. Estimations of the length resistance relation of mercury strain gauges agreed well with the theoretically expected function. If an inextensible part is inserted into the circumferential arrangement of the filament, a correcting calculation of volume changes is necessary.

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