Ventricular performance, pressure-volume relationships, and O₂ consumption during hypothermia

Abstract

Left ventricular performance in the isolated heart of a dog was observed at normal temperatures (37.7 C) and under hypothermia (32.2 C) at comparable heart rates. The peak pressure of isovolumic contractions at the same ventricular end-diastolic pressures averaged 40% higher at the lower temperature. Diastolic pressure-volume relationships were similar at both temperatures. In studies in which the ventricle ejected fluid and performed work the hypothermic ventricle was capable of performing greater work at comparable heart rates, left ventricular end-diastolic pressures, and loading. When the ventricle was allowed to perform work by compressing air into a chamber of constant volume left ventricular oxygen consumption (Vo2) increased with the peak systolic pressure as the temperature was lowered. If the peak systolic pressure was maintained constant by increasing the volume of the air chamber as the temperature was lowered no consistent relationship could be shown between left ventricular Vo2 and the integral of systolic pressure in time which invariably increased with hypothermia.

Hypothermia preserves myocardial function and mitochondrial protein gene expression during hypoxia

“…Consistent with previous studies (13,21) hypothermia also produced an increase in respiratory efficiency of cardiac work-assessed by-product of developed pressure and heart rate-to-MVO 2 ratio. Thus the hypothermia-perfused rabbit heart requires less carbon substrate oxidation per unit contractile work than the normothermic counterpart.…”

Norepinephrine Release and Left Ventricular Pressure in the Isolated Heart

“…From this figure it is evident that the performance of the isovolumically contracting ventricles declined relatively rapidly compared with the performance of those allowed to eject a constant volume. It should be noted that the initial peak systolic pressure of ventricles contracting isovolumically was greater on the average than that of ventricles ejecting saline, as has been documented previously (6,8). While the ventricles contracted at a constant …”

“…In view of previous studies which show that at a given end-diastolic pressure the capacity of a ventricle to develop pressure decreases as the volume of saline ejected is increased, one can assume that the isovolumically contracting ventricles were developing the highest pressures that they could without sympathetic nervous stimulation or the administration of substances having a positive •Initial or final peak systolic intraventricular pressure was zero when A pressure was positive or negative, respectively. inotropic effect (6,8). Whether the decline in performance of an isovolumically contracting ventricle is the result of the development of pressure or whether it is due to some other quality intrinsic to an isovolumic contraction cannot be answered, as the development of pressure is, by necessity, a concomitant to an isovolumic contraction.…”

“…The isolated heart preparation has been fully described in previous publications and will be outlined only briefly herein (6)(7)(8). Schematic diagrams of the preparation are found in Figures 1 and 2.…”

The ventricular pressure-volume diagram revisited.

“…When the amount of air in the ventricular loading system was increased from a minimum to larger amounts, the slope of the P-V diagram of the auxobaric contractions decreased from nearly 90° to smaller values. However, the end-systolic P-V data points gathered around a straight line except for one point in the Volume mi 10 …”