Vascular responses to temperature in the foot of the giant fulmar,Macronectes giganteus
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Blood circulation to the leg of an antarctic bird, the giant fulmar,Macronectes giganteus, has been studied in response to changing the temperature of the ambient environment including immersion of the feet in ice water.
Measurements done include blood flow to the leg by an electromagnetic flow meter, blood pressure in the carotid artery and locally in a leg artery and vein, intravenous and arterial blood temperatures in the leg in addition to foot subcutaneous temperature and core temperature (deep pectoral temperature).
Blood flow to the lower leg varied between 10 ml/min and 40 ml/min during resting thermoneutral conditions.
Raising the core temperature by heating the central body increased foot blood flow to maximum values around 40 ml/min or 160 ml/min/100 g tissue.
Quick warming of the cold feet by immersion in hot water caused only slight increase in leg blood flow, whereas slow rewarming in air gave increasing leg blood flow when the local temperature of the foot increased from near zero to 35.6° C.
Sudden immersion of the foot in ice water (T = −2.0° C) elicited an immediate flow increase and a transient increase in foot arterial blood temperature. Venous pressure in the foot increased with blood flow while foot arterial pressure was unaltered.
The vasodilatation on ice immersion, termed the “cold flush” was followed by a gradual increase in vasoconstriction and reduced blood flow. After about 3 minutes fluctuations “huntings” appeared in leg blood flow and local temperatures in the foot.
The described circulatory changes are discussed in relation to thermal homeostasis of the bird and protection of the naked feet from cold shock and impairment of function on sudden cold exposure. Special reference is given to the phenomenon of cold vasodilatation earlier described on cold exposure of extremeties in mammals.
KeywordsCore Temperature Cold Exposure Blood Temperature Giant Fulmar Arteriovenous Anastomosis
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