Vascular resistance and arterial pressure in autoperfused dog hind limb

¹ Department of Physiology, and Heart Research Center, Indiana University School of Medicine, Indianapolis, Indiana

Arterial and venous vascular resistance was studied in 30 isolated dog hind limbs. The preparations were autoperfused from the contralateral femoral artery through a short piece of polyethylene tubing. By application of the isogravimetric technique of Pappenheimer and Soto-Rivera the capillary pressure was determined and the arterial and venous resistances were separately calculated. As arterial pressure in the limbs was progressively reduced from approximately 100 mm Hg down to 20 mm Hg the arterial resistance decreased in 25 of the 30 experiments. The reduction in resistance was particularly evident at arterial pressures below 50 mm Hg. The venous resistance remained relatively constant as the arterial pressure was reduced; a significant rise was seen in only three experiments. Arterial and venous blood oxygen and carbon dioxide contents were determined at various levels of blood flow in ten of the experiments. In general, as the blood flow was decreased, venous oxygen content decreased and carbon dioxide content increased, while oxygen consumption fell. It is concluded that autoregulation of blood flow in the hind limb may, in part, be due to tissue hypoxia. It cannot be explained by the tissue pressure hypothesis.