Rapid and Slow Components of the Circulation in the Human Forearm1

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

“…The source of subjects, experimental technique, methods of analysis and calculation of results were identical to those previously described (1). The ratio of blood flow in the rapid component (fQ) to that in the slow (f2) was estimated from the mean circulation times of the total curve (T), the rapid component (t1), and the slow component (t) as described in a previous paper (1). The parameters fL/f2 and tA/t, were used to estimate the ratio of the 1 Supported in part by United States Public Health Service Grants H-720 and H-1903 (National Heart Institute).…”

“…The ratio of flows rather than absolute blood flows were estimated because the distribution of dye in the various branches of the brachial artery may not be uniform, and hence, the peripheral vasculature of the forearm cannot be regarded as a uniform mixing chamber (1).…”

“…Hyperemia restricted to the forearm under study was produced by the following techniques: 1) by the local intra-arterial injection of 5 mg. tolazoline (Priscoline*).…”

“…(Submitted for publication July 23, 1957;accepted February 20, 1958) 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 (1)(2)(3). Since pressures are very nearly equal at either end of an anastomotic intercapillary or intervenular channel, flow may be sluggish in that channel.…”