Abstract
Protective and injury effects of hypothermia both have been reported. Mild hypothermic protection has been paid much attention since the last decade. A protective threshold (30°C) has been reported in the isolated hearts. This study was to detect if a similar threshold exists in the intact animals. Under propofol anesthesia, the cardiopulmonary bypass (CPB) was performed in pigs. The esophagus temperature was decreased from 35°C to 20°C by using a heart-lung machine. A decrease in heart rate was parallel to the reduction of temperature. The cardiac contractility (dP/dt max) and performance (power, cardiac output etc.) showed a sigmoid curve-like change: there was a high plateau (100±4.4% of baseline value) at 35–29°C; a low plateau (16±6.0%) at 24–20°C; and a steep slope between 28–25 °C. Arrhythmia and tremble occurred at the slope part of the curve. Accordingly the pigs were treated with these 3 temperatures 40 min prior to and 60 min during cardioplegic ischemia. The functional recovery was calculated as % of baseline values during reperfusion, such as dP/dt max recovery was 39±13%, 9±6%, and 130±5% in 34–35, 20, and 29–31.5°C groups, respectively (P<0.01) without the heart-lung machine. In conclusion, the hypothermia injury threshold is 28°C and the optimal protective temperature is 30.5±1°C during CPB in pigs.
Published Version
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