Cardiac pumping ability was assessed during the natural development of left ventricular hypertrophy by elevating venous pressure by infusing Tyrode's solution intravenously to produce peak cardiac output. This experiment was performed on spontaneously hypertensive rats (SHR) of three age groups (11, 24, and 83 weeks). From 11 to 24 weeks, peak cardiac output of SHR increased in direct proportion to the abnormally increased ventricular mass; Thus peak cardiac output per gram of left ventricle (LV) remained stable. Similar results were obtained for two strains of normotensive rats at each of the same three age groups. Thus, in the normotensive animal peak cardiac output per gram of LV remained stable over a wide range of ages and varying left ventricular weights. However, with progressive elevation of arterial pressure in aging SHR (83 weeks), we observed severe ventricular hypertrophy (100% increases in left ventricular to body weight ratio). In this oldest SHR group, unlike age-matched normotensive rats, there was a marked reduction in the pumping ability per gram of LV. Thus, during the natural development of left ventricular hypertrophy SHR demonstrated both a stable stage of hypertrophy in which the increased left ventricular mass maintained its pumping ability, and a later stage of deterioration in which there was a loss of the normal relationship between ventricular mass and pumping ability.
Pfeffer et al. (Sat,) studied this question.