Mild hypothermia impairs left ventricular diastolic but not systolic function.

Hypothermia is a component of myocardial protection during cardiopulmonary bypass (CPB) and cardioplegic arrest (CA). Patients in the early post CPB period often show mild hypothermia and cardiac dysfunction. We sought to investigate the impact of hypothermia on left ventricular (LV) function. Anesthetized dogs (n = 12) were instrumented with myocardial ultrasonic crystals and LV micromanometer. Systolic function was measured by preload recruitable stroke work (PRSW). Diastolic function was measured by -dP/dt(max) and tau. In six dogs (Norm group), body temperature was maintained at baseline levels. In another six dogs (Hypo group), body temperature dropped gradually over the time course of the experiment. The body temperature in the Hypo group decreased from 37.0 +/- 0.3 degrees C to 35.2 +/- 1.0 degrees C. -dP/dt(max) decreased and tau increased significantly with hypothermia but were stable in the Norm group. Both tau and -dP/dt(max) showed a linear relationship to the body temperature (r =.91 and r = .93, respectively). PRSW did not change and cardiac output decreased with hypothermia. Thus, even mild hypothermia impairs LV diastolic but not systolic function. Cardiac output is temperature sensitive and therefore rewarming of patients post-CPB has priority.