Positive tissue fluid pressure in the feet of antarctic birds

Abstract

Tissue fluid pressure in the web feet of antarctic birds rises from negative to positive during warming (+6 cm H 2O per 25°). Fluid pressures in peritonea and thighs remain in a normal negative range irrespective of thermal milieu. Since no edematous swelling is apparent in the feet during warming, web foot compliance is low. The low compliance probably results from the quilted arrangement of connective tissue in the web foot. Cooling of web feet produces a response in fluid pressure opposite to warming. This fall in fluid pressure, however, occurs at a slower rate (−4 cm H 2O per 24°). The development of positive fluid pressure probably results from higher web foot blood flow, a thermoregulatory response prevalent in these birds during warming.