Cardiovascular responses in prolonged hypothermia

Abstract

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.