Blood flow changes in the duck during thermal panting

Abstract

Carotid and sciatic blood flow have been measured in resting and panting Pekin ducks using electromagnetic flowmeters. Panting induced by high ambient temperature caused the carotid blood flow to increase from 9.6 to 26.0 ml min-1, while the sciatic flow declined slightly from 41.6 to 38.1 ml min-1. During panting breathing rate increased 10--20 times, but there were no significant changes in heart rate and mean arterial blood pressure. The carotid peripheral resistance was therefore greatly reduced, whereas sciatic resistance remained unchanged or increased slightly. The vascular beds perfused by the sciatic (legs) and carotid (upper respiratory tract) arteries are both important for heat dissipation. This study shows that when heat dissipation from the naked legs becomes inefficient due to high ambient temperature, blood flow in the sciatic tended to decline while conversely panting was associated with a large increase in carotid flow.

Blood flow through arteriovenous anastomoses and its thermal function in the laying hen.

“…The shift in body temperature on warming was small, 0 4 0C, which brought body temperature to 42-1 0C, a temperature at which peripheral vasodilation is already established whereas panting is at its onset (Whittow, 1976). Such a body temperature increment was not associated with an increase in blood flow to the leg in the ducks (Bech & Johansen, 1980). The data presented here indicated that the increase in metatarsal skin temperature from 31 0C in the control state to 38 TC on warming was associated with an increase in t.b.f.…”

Avian Adjustments to Cold

“…Respiratory heat loss is thus of interest in the context of this review. Birds possess capacities for oxygen extraction that allow substantially lower ventilation than in mammals of comparable size (Bernstein and Schmidt-Nielsen 1974;Bech and Johansen 1980) and this should put them in a more favorable position concerning restriction of respiratory heat loss. Additionally, many species increase the efficiency of oxygen extraction at cooler Ta's, allowing a lower rate of ventilation than would otherwise be required (Bucher 1981(Bucher , 1985Brent et al 1983Brent et al , 1984Bech et al 1984).…”