A Comparison of Procedures for Increasing Blood Flow to Limbs Using an Improved Optical Plethysmograph

Measuring the minute volume of blood flow through an extremity at rest, or in response to a physiological stimulus, offers a useful means of evaluating the status of its vascular bed. Hewlett and Van Zwaluwenburg (1) used for this purpose a plethysmograph based upon the principle demonstrated by Brodie (2) wherein sudden occlusion of the veins draining the limb produces an increase in limb size, which can be used as a measure of arterial inflow. If a limb is enclosed in a rigid container the increase in volume can be recorded in a variety of ways. Hewlett and Van Zwaluwenburg (3) used air conduction and optical recording; more recently others have used water or water and air conduction with a Brodie bellows, Gad volume recorder, or a piston recorder. Experience has shown us that these latter methods have concealed errors which become apparent when replaced by air conduction and optical recording. These are: (a) errors in calibration due to a non-rigid closure of the open end of the plethysmograph, (b) errors due to involuntary movement of the extremity into and out of the plethysmograph, (c) errors produced by rising intravascular tension secondary to venous obstruction, (d) errors due to the effect of displacement of blood from beneath the collecting cuff. This report concerns itself with a study of these errors, with means of eliminating them, and with a comparison of five procedures commonly used to produce dilatation of the vascular bed in the lower extremity.