Temperature Changes in the Blood of the Pulmonary Artery and Left Atrium of Dogs During Exposure to Extreme Cold

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Abstract
Polyethylene cannulae were surgically placed in the pulmonary artery and left atrium of dogs; thermistors mounted in polyethylene tubing and hypodermic needles, were passed through these cannulae and the temperature changes of the blood and rectum were recorded photographically. Continuous recordings of these temperature changes in unanesthetized dogs were made when the experimental animals were suddenly exposed to an ambient temperature of –35°C for 30 minutes. Shivering began immediately after exposure to cold; blood and rectal temperatures increased 0.4–0.5°C during the 30 minutes of exposure. It was found that the rectal temperature exceeded the left atrial blood temperatures from 0.2 to 0.3°C, and that in all experiments except one, the left atrial blood temperature exceeded that of the pulmonary artery from 0.01 to 0.15°C. Increased metabolism, along with cutaneous vasoconstriction probably explains the rise in blood and rectal temperatures during exposure to cold. Thermodynamic considerations of carbon dioxide and oxygen exchanges in the lungs lend support to the findings regarding the pulmonary artery-left atrial blood temperature gradient.

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