Left ventricular contractile performance in the early stage of hypertension in humans

The aim of the present study was to assess how cardiac structural changes c ontribute to increasing left ventricular pump function during exercise in s ubjects with mild hypertension. In 23 young male subjects with mild hyperte nsion and 12 male normotensive control subjects. left ventricular function was measured echocardiographically using the fractional shortening meridion al stress relationship at rest and during longlasting exercise at the anaer obic threshold. Mean exercise duration and intensity were 61 (SEM 1.7) min and 71.3 (SEM 2.5)% (V)over dotO(2max) (maximal oxygen uptake), respectivel y, in the hypertensive subjects, and 63 (SEM 1.5) min and 75.7 (SEM 2.2)% ( V)over dotO(2max), respectively, in the normotensive subjects (all differen ces = n.s.). Left ventricular fractional shortening was measured both at th e endocardium and at the midwall. In the hypertensive subjects the endocard ial fractional shortening, predicted on the basis of the shortening/stress relationship in the normotensive controls, overestimated midwall fractional shortening throughout rest (P = 0.04) and exercise (P = 0.004). To study h ow an increase in left ventricular wall thickness contributed to increasing ejection performance during exercise, the hypertensive subjects were divid ed according to whether their relative wall thickness was less than 0.35 or equal to or greater than 0.35. Subjects with relative wall thicknesses equ al to or greater than 0.35 had a depressed myocardial contractility at rest (P = 0.0001). During exercise they increased their stroke volume and cardi ac output adequately through an increase in ejection performance, while myo cardial contractility remained subnormal (P < 0.0001). In conclusion, the p resent results indicated that in mildly hypertensive subjects an increased left ventricular wall thickness is crucial in preserving left ventricular p ump function during exercise.