Reactive hyperaemia in the hind limbs of the rabbits. III. The effect of hypervolemia and venous congestion.

The effect of increased circulatory fluid volume and local venous congestion on reactive hyperaemia was studied in the hind limbs of rabbits. Compared with controls, hypervolemia reduced maximal flow significantly after all occlusion times. Percentual repayment decreased after 10 second occlusions, increased above control level after 60 second occlusions, and otherwise was similar to controls. Hypervolemia increased recovery time significantly after occlusions longer than 10 seconds. It is possible that decreased oxygen carrying capacity of the blood due to decreased haematocrit after infusion can explain the increased repayment observed during hypervolemia. Furthermore, oedema formation may to some extent prolong the wash-out of metabolites in the postischaemic period. During venous congestion, maximal flow, percentual repayment as well as recovery time were significantly reduced after all occlusion times. Venous congestion may represent an increased resistance against blood arriving from the arterial side after release of the arterial occlusion, thereby reducing the initial part of reactive hyperaemia and perhaps a major part of the hyperaemia after short occlusions. In addition the congested blood may represent an increased amount of oxygen made available for the tissue, and finally venoarterial reflexes may contribute to the reduction of reactive hyperaemia during venous congestion. These results show that factors such as circulatory blood volume and venous pressure and blood volume of the local vascular bed affect reactive hyperaemia significantly.