The Effects of a Variety of Hemodynamic Changes on the Rapid and Slow Components of the Circulation in the Human Forearm1

When a tracer substance which does not diffuse through the capillary walls is introduced into the brachial artery and the effluent blood is sampled continuously thereafter, a time-concentration curve of the labeled substance may be plotted which describes the velocity-flow pattern of the blood in the forearm ( 1) . It was found that the descending limb of the time-concentration curve usually was biphasic. Evidence was presented which indicated that these biphasic curves were not due to differences in path lengths or to velocity flow through different tissues such as skin and muscle. It was suggested that this biphasic pattern was due to two basically different rates of flow in the highly anastomotic small vessel circulation (l-3). Since pressures are very nearly equal at either end of an anastomotic intercapillary or intervenular channel, flow may be sluggish in that channel. Direct observation of the circulation in the hamster cheek pouch disclosed that varying rates and direction of Aow occur in the anastomotic channels-at times rapid, at times slow, at times surging, stopping or reversing. It seemed of interest to determine what effect changes in both the local and general circulation would have upon the characteristics of this biphasic velocity-flow pattern in the forearm.