Influence of aortic pressure-induced homeometric autoregulation on myocardial performance.

CLANCY, RICHARD L., THOMAS P. GRAHAM, JR., JOHN Ross, JR., EDMUND H. SONNENBLICK,AND EUGENE BRAUNWALD. InJuence of aortic pressure-induced homeometric autoregulation on myocardialperformance. Am. J. Physiol. 214(5) : 1186-l 192. 1968.The alteration in left ventricular (LV) performance following aortic pressure-induced homeometric autoregulation, defined by a fall in LV end-diastolic pressure after a sudden increase in aortic pressure (AP), was assessed in terms of the mechanics of LV contraction. The relative contributions of the accompanying Frank-Starling mechanism and altered contractility, or inotropic state, were measured from the force-velocity (F-V) relations of single isovolumic contractions in a dog right-heart bypass preparation, the relations during homeometric autoregulation and during increased LV filling at constant aortic ‘pressure being compared at equal LV end-diastolic circumferences (LVEDC). Mean values following the homeometric autoregulatory response and during increased LV filling were, respectively : mean AP 113 and 78 mm Hg, LVEDC 20.2 and 20.2 cm, LVEDP 8.7 and 9.9 mm Hg, and stroke volume Il.3 and 18.9 ml. The isovolumic F-V curves were shifted to the right following AP elevation, maximum stress and contractile element velocity being 7.4 and 7.3% larger than during increased LV filling. These results suggest that the increase in LV performance during the steady state after pressure-induced homeometric autoregulation has occurred is associated with a small augmentation of LV contractility, but that the major effect results from the operation of the Frank-Starling mechanism.