Measurement of organ blood flow using tritiated water. I. Hind limb muscle blood flow in conscious ewes.

Blood flow rates to a hind limp preparation, consisting predominantly of muscle, were obtained with tritiated water (TOH) diffusion and radioactive microsphere technique in four conscious ewes (a total of seven comparisons). During the continuous infusion of TOH, equilibrium between muscle and its venous drainage was attained by 40--60 min after the start of the infusion. Total blood flow to the hind limb measured using TOH was corrected for arteriovenous anastomosis flow to provide a measure of capillary blood flow through the hind limb. The capillary blood flow rates so obtained using TOH were highly correlated with those measured directly in muscle with microspheres (ml min-1, r = 0.934; ml 100 g-1 min-1, r = 0.886, P less than 0.01, n = 7) and the corresponding mean flow values obtained with the two techniques (respectively, 104.6 +/- 15.1 v. 106.5 +/- 14.9 ml min-1 and 7.2 +/- 0.8 v. 7.3 +/- 0.8 ml 100 g-1 min-1) were not significantly different. There were substantial difference in the capillary blood flow rates for the individual muscles of the hind limb.