AJP - Heart and Circulatory Physiology, Vol 259, Issue 6 1789-H1795, Copyright © 1990 by American Physiological Society

ARTICLES

Vascular mechanics of venous drainage in dog hindlimbs

S. Magder
Division of Critical Care, Royal Victoria Hospital, Montreal, Quebec, Canada.

The time constant of venous drainage (tau v) of a vascular bed is an important determinant of the change in regional volume that will occur with a change in blood flow or venous pressure (Pv). Therefore, to measure tau v of the dog hindlimb, the vasculature was isolated and perfused with a pump. Inflow and outflow were measured with electromagnetic flow probes. Blood volume was changed (delta V) by changing flow (delta Q), and a double-occlusion procedure was used to obtain the venous elastic recoil pressure (Pel) from the plateau of Pv. Venous resistance (Rv), compliance (Cv), and tau v could then be calculated. Rv was 7.7 +/- 1.4 mmHg.ml-1.min.100 g-1 and Cv was 0.59 +/- 0.25 ml/mmHg, tau v calculated from the product of Rv and Cv was 4.20 +/- 1.58 s and from the ratio of delta V to delta Q was 4.95 +/- 1.53 s (P = NS) at a mean Pel of 17.6 +/- 3.7 mmHg. delta V was also produced by changing Pv; the average tau v (1.95 +/- 0.37 s), was shorter than that with changes in flow. Finally, a ramp increase in flow was used to calculate tau v from the time delay between inflow and outflow. tau v by this method was longer (6.06 +/- 1.70 s) and was probably influenced by the change in Pv. In conclusion, the hindlimb has a short tau v of venous drainage and would not be expected to store large volumes of blood even with large increases in blood flow.

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