Regulation of external work of concentric hypertrophied left ventricles in unanesthetized hypertensive dogs.

This study aimed to evaluate the change in external work and its control mechanism in the concentric hypertrophied heart induced by systemic hypertension. The calculated stroke work, myocardial contractility, afterload, and preload were examined in the baseline period (Control Stage, CS) and in the eighth week after the induction of perinephritic hypertension (Hypertensive Stage, HS) in unanesthetized dogs. These variables were examined with echocardiograms and high-fidelity left ventricular (LV) and ascending aortic pressures. Mean aortic pressure was significantly (p less than 0.05) elevated from 95 +/- 10 to 134 +/- 27 mmHg in HS. The ratio of end-diastolic wall thickness to radius significantly (p less than 0.05) increased in the HS. The calculated stroke work of the LV chamber was significantly (p less than 0.05) increased from 7022 +/- 1203 to 8860 +/- 1548 X 10(3) erg in HS while the stroke work normalized for wall thickness by calculating the wall stress was not altered (3069 +/- 1086 v.s. 2989 +/- 866 erg; CS v.s. HS) with no significant change in heart rate in HS. In the HS, the end-systolic wall stress (afterload) and the slope of end-systolic wall stress-dimension relationship (myocardial contractility) were unchanged while the end-diastolic wall stress (preload) slightly reduced. These results suggest that, in the concentric hypertrophied left ventricle induced by systemic hypertension, the LV myocardial external work is normal, whereas the LV chamber external work increases.(ABSTRACT TRUNCATED AT 250 WORDS)