Feline left ventricular oxygen consumption is not affected by volume expansion, ejection or redevelopment of pressure during relaxation.

We studied the dependency of myocardial oxygen consumption on the mechanical events during left ventricular relaxation in isolated supported cat hearts. The volume of the left ventricle was controlled by means of a balloon connected to a membrane pump. Oxygen consumption (MVO2 in cm3.min-1.100 g-1) for three protocols (PROT) performed at peak isovolumic pressure, was studied: (1) rapid ejection to zero pressure, (2) partial rapid ejection followed by redevelopment of pressure, (3) volume expansion during relaxation, and compared with oxygen consumption of isovolumic (ISOV) beats. We found (mean +/- SD): (table; see text) In the protocols 1 and 3 the differences were not significant (paired Student's t-test, p greater than 0.05). In protocols 1 and 2 left ventricular volume was decreased up to 2.15 cm3 (i.e. stroke volume, SV) during the pressure release. We studied the specific effect of ejection (i.e., wall muscle shortening) in a fourth protocol in which the ventricle ejected up to 2.7 cm3 under nearly zero pressure load (isobaric contraction). There was a small amount of oxygen consumption associable with this unloaded ejection i.e. MVO2 = 3.38 (+/- 0.47) + 0.30 (+/- 0.16) SV, but it was too small to compensate for a decrease in MVO2 expected from the pressure release according to the tension time index. These findings suggest that oxygen consumption does not depend on the mechanical events during ventricular relaxation.