Coronary pressure-flow relation in left ventricular hypertrophy. Importance of changes in back pressure versus changes in minimum resistance.

Abstract

Perfusion abnormalities in the pressure-overloaded hypertrophied left ventricle could result from an increase in minimum coronary resistance or an increase in effective back pressure due to increased extravascular compressive forces. Since the pressure-flow relation of the maximally vasodilated coronary bed allows dissociation of minimum resistance (inverse slope [1/alpha PF]) and back pressure (pressure at zero flow [Pf = 0]), the present study was undertaken to examine the coronary pressure-flow relation in left ventricular hypertrophy (LVH). Ascending aortic banding in eight dogs at 6-8 weeks of age (LVH group) increased the left ventricular to body weight ratio to 8.7 +/- 0.6 g/kg as compared with 4.8 +/- 0.2 g/kg in nine normal dogs (p < 0.05). Maximum coronary vasodilation was produced by infusion of adenosine (1 mg/kg per minute i.v.). The slope of the coronary pressure-flow relation (alpha PF) was 5.8 +/- 0.5 10(-2) (ml/min per gram)/mm Hg in the LVH group and 9.3 +/- 0.6 10(-2) (ml/min per gram)/mm Hg in the normal group (p < 0.05). alpha PF was significantly correlated with the left ventricular to body weight ratio but not with coronary pressure, suggesting that the degree of hypertrophy and not exposure to high coronary pressure was responsible for the observed decrease in alpha PF. Pf = 0 was 24.1 +/- 2.6 mm Hg in the LVH group and 11.7 +/- 1.2 mm Hg in the normal group (p < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)