The absence of temperature effects on end-diastolic pressure-volume relations in the canine left ventricle determined by two-dimensional echocardiography

Abstract

Because of divergent conclusions in the literature regarding the effects of temperature on end-diastolic compliance in the canine left ventricle (LV), pressure-volume relationships at normothermia and hypothermia (28 degrees C) were studied with two-dimensional ultrasound in nine dogs on cardiopulmonary bypass (open pericardium) over a range of left ventricular end-diastolic pressure (LVEDP) from 0 to 22 mm Hg. Three perpendicular echocardiographic sections were used with Simpson's rule to measure LV volume and mass at end-diastole for each level of LVEDP. Temperature was varied between 37 degrees and 28 degrees C by systemic cooling, and heart rate was allowed to slow spontaneously with temperature reduction. There was no change in left ventricular end-diastole pressure-volume (LVEDP-LVEDV) relationships at lower temperature provided that ventricular relaxation was complete at end-diastole. In addition, serial postmortem pressure-volume curves carried out by direct saline infusion into sealed ventricles at 38 degrees and 28 degrees C in three additional dogs demonstrated no temperature effects on postmortem LV compliance. Postmortem mass correlated well with echocardiographically determined LV mass, which showed a significant increase during the period of cardiopulmonary bypass, correlating with the development of myocardial edema. In summary, there appears to be no effect of moderate hypothermia on LVEDP-LVEDV relationships, provided the heart is in true diastasis at end-diastole. In addition, echocardiographic techniques can be used to study LV mass change on cardiopulmonary bypass.