Cardiovascular responses in prolonged hypothermia

¹ Department of Physiology, Emory University Medical School, Atlanta, Georgia

Rats cooled to a body temperature of 15 C live for 9–10 hr. However, they do not survive the rewarming if the hypothermia has lasted more than 5 hr. Neither the cause of death in hypothermia after 10 hr, nor the cause of resuscitation failure of animals rewarmed after 5 hr in hypothermia is known. In 31 rats cooled to and maintained at a body temperature of 15 C, cardiac output decreased continually during the entire period of hypothermia, having by the end of hypothermic survival the value of only 25% of output at the beginning of the hypothermic period. The arteriovenous differences of O₂ content increased, while total peripheral resistance increased continuously during this time. During the 10 hr of hypothermic survival the hematocrit ratio rose from 42 to 65–70 vol %. Because of these changes it is suggested here that the failure of circulation is the probable cause of death in hypothermia.

Key Words: cardiac output • survival time • oxygen consumption • blood oxygen content • arterial blood pressure • total peripheral resistance • muscle blood flow • white rat

Submitted on April 5, 1965

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