Left ventricular O2 requirements of pressure and volume loading in the normal canine heart and inaccuracy of pressure-derived indices of O2 demand.
The purpose of this study was to: 1) re-evaluate the left ventricular O2 requirements (MVO2) of pressure and volume-loading; and b) assess the accuracy of pressure-derived indices of left ventricular (LV) O2 demand under pressure-loading and volume-loading conditions. Using a right heart bypass preparation (heart rate 150 beats . min-1), mean arterial pressure (7.3 to 22.9 kPa) and cardiac output (0.8 to 6.0 litre . min-1) were varied independently. Adequate left ventricular O2 supply was demonstrated by normal transmural distribution of blood flow, normal myocardial lactate metabolism, and intact reactive hyperaemic responses. For equivalent increases in cardiac external work (from 2 to 4 joules . min-1) pressure-loading and volume-loading resulted in similar increases in O2 uptake (59% and 49%, respectively, P = 0.21). MVO2 was consistently greater for volume-loading than for pressure-loading at any SPTI, pressure-rate product, and triple product. The prediction of O2 demands by these indices under these loading conditions collectively was unreliable (r = 30 to 0.42). O2 requirements of the left ventricle with both pressure-loading and volume-loading were highly correlated (r = 0.82 to 0.99) with meridional wall stress. We conclude that: 1) volume-loading conditions have a greater O2 requirement than appreciated previously; 2) pressure loads and volume loads require similar O2 uptake in the normal canine heart for similar external work; 3) currently used pressure-derived indices are unreliable predictors of LV O2 demand when loading conditions are varied; and 4) O2 requirements are more uniformly related to meridional wall stress.
D000818:Animals; D001794:Blood Pressure; D002302:Cardiac Output; D003326:Coronary Circulation; D004285:Dogs; D006321:Heart / Q000502:physiology*; D006339:Heart Rate; D009206:Myocardium / Q000378:metabolism*; D010101:Oxygen Consumption