Blood Flow in Small Blood Vessels During Deep Hypothermia

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Abstract
The minute blood vessels of rat mesocecum and hamster cheek pouch were examined before and during whole-body hypothermia or during local cooling. Blood ceased to flow in about half the observed vessels at 20° C. (rat) or 10°–5°C (hamster). Arterioles, capillaries and venules did not change their mean calibers, hence vasoconstriction was not the rule. Linear velocity decreased in observed blood vessels. In hypothermia arterial blood pressure is known to remain high while pulse rate and cardiac output decrease greatly. Changes in blood viscosity account for nearly all the estimated increase of resistance, and narrowing of blood vessels in the tissues observed proves unimportant in upholding arterial pressure. Submitted on May 6, 1957