Digital Blood Flow: I. Correlative Study of the Electrical Impedance and the Venous Occlusive Plethysmographs.

V ENOUS OCCLUSIVE PLETHYSMOGRAPHY for the measurement of digital blood flow is widely accepted in spite of its limitations .1'2 On the other hand, the electrical impedance method, although believed to give an accurate measurement of digital blood flow,3 had not received the same clinical trials in spite of the ease with which these measurements are performed and its sensitivity to rapid changes when the extremity is exposed to various stimuli.4 The purpose of this study was to correlate the values obtained by these two methods in normal individuals and to investigate the effect of environmental temperature on the obtained values. METHODS AND MATERIALS The electrical impedance plethysmo-graphic method used was a modified tetra-polar method described by Nyboer.' The input electrodes and the two stainless steel sampling electrodes were placed 4 cm. apart on a wide bandage made from overlapping strips of adhesive tape to assure the maintenance of the correct spacing when in position on the middle digit of one hand. The proximal input electrode was placed around the wrist by the use of a second Southwestern Medical School. piece of tape. The electrodes were covered with electrocardiogram electrode paste to assure good contact with the skin. The volume of the finger between the sampling electrodes was calculated as a frustrum of a cone. The hand was placed at the side and kept covered with a hospital sheet at all times. The pulse waves were recorded on an Electronics for Medicine recorder. The digital blood flow was expressed in ml. of blood per 100 cc. of tissue per minute. The venous occlusive plethysmograph was placed on the middle digit of the opposite hand. The finger was invaginated in a rubber glove finger, and the covered finger was surrounded by a circulating controlled temperature water bath kept at 320 to 33#{176}C. A Gaertner cuff was placed immediately adjacent to the plethysmograph and served as a gasket when inflated. Pressure differences were measured by a Statham strain gauge and recorded on the previously mentioned recorder. The hand and fingers not in the plethysmograph were covered by a sheet and rested on cotton pads at the side. Several occluding pressures were used in each experiment. The flow was calculated by taking the tangent of the slope produced by the occlusive pressure. The unit of flow was again ml. of blood per 100 cc. of tissue per minute. The subject was in a …