CAPILLARY DIAMETER CHANGES DURING LOW PERFUSION-PRESSURE AND REACTIVEHYPEREMIA IN RABBIT SKELETAL-MUSCLE

Capillary diameter changes were studied in the tenuissimus muscle of 2 9 urethan-anesthetized New Zealand White rabbits. Capillaries were vis ualized with transillumination bright-field microscopy (saltwater lens , x 50; resolution approximate to 0.3 mu m). Median capillary diameter during the control period was 4.4 mu m (range 3.2-6.9 mu m). Complete aortic occlusion resulted in a reduction of median femoral arterial p ressure to 17 mmHg (range 4-22 mmHg). During 2 min of occlusion, capil lary diameter decreased by 6%, with greater change on the arteriolar s ide of the capillary than on the venular side. During reactive hyperem ia after release of the occluder, capillary diameter maximally increas ed by 12% compared with the control period, with a larger response at the arteriolar end of the capillary than at the venular end. Median ca pillary resistance was estimated to increase by 27% during occlusion a nd to decrease by 36% during peak reactive hyperemia. The observed dia meter changes are compatible with the idea that capillaries change the ir diameter relative to changes in transmural pressure.