ARTERIOVENOUS SHUNTING IS NOT ASSOCIATED WITH VENOUS CONGESTION IN BONE - KNEE TAMPONADE STUDIED WITH 15-MU-M AND 50-MU-M MICROSPHERES IN IMMATURE DOGS

Blood flow in the hind-limb bones of 8 immature labrador dogs with unilateral knee joint tamponade at 75 percent of the mean arterial pressure was measured with 15-mu-m and 50-mu-m microspheres to determine whether or not arteriovenous shunting occurs in bone with venous congestion caused by increased outflow resistance. The intraosseous pressure was 43 percent of the mean arterial pressure in the experimental distal femoral epiphysis versus 14 percent in the control knee (P < 0.001). No pressure changes were found in the distal femoral metaphysis. Regional blood flow with 15-mu-m microspheres decreased centrally in the distal femoral epiphysis and increased centrally in the proximal tibial epiphysis. Metaphyseal blood flow was largely unchanged. A net shift in the preferred embolization site of 50-mu-m microspheres from central to peripheral regions occurred within both juxta-articular epiphyses, indicating arteriolar vasodilation, but the relation between the uptake of the two microsphere sizes was unchanged when the epiphyses and other bony flow compartments were viewed in toto. The result speaks against the hypothesis of arteriovenous shunting in intraosseous hypertension.