Key result
Hypothermia of 25 C for 24 hours in dogs led to diminished oxygen and substrate utilization, with myocardial glycolysis beginning after 12 hours and signs of myocardial hypoxia after 24 hours.
Why the study?
Does hypothermia of 25 C for 24 hr alter myocardial metabolism and efficiency in anesthetized dogs?
Does hypothermia of 25 C for 24 hr alter myocardial metabolism and efficiency in anesthetized dogs?
Prolonged hypothermia (25 C for 24 hr) in dogs induces myocardial hypoxia and shifts metabolism away from carbohydrates, indicating a limit to cardiac tolerance of cooling.
Answers are grounded in this paper and cite their sources.
Signals limit to cardiac tolerance of prolonged moderate hypothermia; hypothesis-generating for clinical cooling protocols.
Effect of hypothermia of 25 C for 24 hr was determined on myocardial metabolism and efficiency in dogs fasted for approximately 15 hr and anesthetized with sodium pentobarbital. Coronary blood flow, cardiac output, myocardial oxygen and substrate utilization, and mechanical efficiency of the heart were determined at normal and reduced body temperatures. Prolonged reduction of myocardial temperature with concomitant reduction in coronary blood flow led to diminished oxygen and substrate utilization. Myocardial glycolysis began after 12 hr of cooling when pyruvate utilization stopped in negative balance. After 24 hr the heart stopped utilizing carbohydrates with negative arteriovenous differences for these substrates (in the presence of normal arterial carbohydrate levels), but continued to utilize nonesterified fatty acid. The coefficient of oxygen utilization for the heart increased following 24 hr of cooling, suggesting a relative state of myocardial hypoxia. The appearance of hypoxia and glycolysis during the late hours of cooling suggests that the limit of tolerance of the heart to cooling was near.
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Russ et al. (1965) studied this question. Hypothermia of 25 C vs. Normal body temperature was evaluated on Myocardial metabolism and efficiency. Hypothermia of 25 C for 24 hours in dogs led to diminished oxygen and substrate utilization, with myocardial glycolysis beginning after 12 hours and signs of myocardial hypoxia after 24 hours.
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