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

¹ Department of Pediatrics, Harvard Medical School, and Cardiology Division, Children's Hospital Medical Center, Boston, Massachusetts

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.

Key Words: left ventricular end-diastolic pressure • cardiac stroke work positive inotropic effect • dog isolated ventricle • ventricular • loading • isovolumetric contractions • contractions • isobaric contractions • myocardial O₂ consumption

Submitted on April 3, 1963

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