Effects of postural changes on arterial to venous blood flow in the dependent limbs of conscious cats

Abstract

It is routinely assumed that the force of gravity can cause blood pooling in the dependent limbs, as venous return from the body region is reduced. However, the effects of postural alterations on blood flow to and from the limbs have not been directly compared or quantified. In the present study, blood flow in the femoral artery and vein of conscious cats were measured using transit‐time ultrasound technology as the animals were rotated head‐up by amplitudes up to 60°. 60° head‐up rotations produced significant (ANOVA, p<0.05) decreases in venous blood flow beginning ≈3 sec following tilt onset, which became maximal at ≈5 sec, with an alteration of 55‐65% from pre‐tilt values. As the animals were maintained head‐up, venous blood flow began to increase, and was 18‐29% lower than pre‐tilt values by 40 sec following rotation initiation. This recovery of venous flow was accompanied by a 17‐34% decrease in arterial blood flow that peaked ≈9 sec after tilt onset. These data confirm that venous return from the dependent limb is greatly attenuated during postural alterations, and the magnitude may be larger than expected. However, the largest perturbation in venous return is transient, and this combined with accompanying decreases in arterial blood flow limits peripheral pooling.