Temperature effects on dog hindpaw series and parallel vascular circuits.

The effect of environmental temperature (skin surface) on distribution of blood flow between the parallel vascular circuits has been assessed in vascularly and neurally isolated hindpaws perfused at constant pressure. The paw was sealed in a chamber filled with water at 10, 20, 30, or 40 degrees C. Peripheral resistance increased as the temperature decreased in both innervated and denervated paws. Resistance in the denervated paws was less than in the innervated paws at all temperatures. Recovery of 85Sr microspheres was less at 40 degrees C than at 10, 20, or 30 degrees C in the denervated paws but did not change in innervated paws. Capillary availability (diffusion capacity and filtration coefficient) increased with each elevation in temperature in both groups. At 10 degrees C both arteriovenous (AV) shunt and capillary flows were low in innervated paws with low capillary and high shunt flow in denervated paws. At 20 and 30 degrees C capillary flow increased with temperature and arteriovenous anastomosis (AVA) flow was unchanged in denervated paws. In innervated paws AV shunt flow fraction slightly increased, with capillary perfusion markedly increased as temperature was elevated. The increased capillary flow in both groups passed through an enlarged capillary bed, whereas the number and/or diameter of AVAs remained essentially unchanged.