Vascular mechanics of venous drainage in dog hindlimbs.
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.
Magder
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Division of Critical Care, Royal Victoria Hospital, Montreal, Quebec, Canada.
D000818:Animals; D004285:Dogs; D006614:Hindlimb / Q000098:blood supply; D011175:Positive-Pressure Respiration; D012039:Regional Blood Flow; D013997:Time Factors; D014655:Vascular Resistance; D014680:Veins / Q000502:physiology*; D014690:Venous Pressure