EXERCISE-INDUCED CARDIAC-HYPERTROPHY IS ASSOCIATED WITH AN INCREASED MYOCARDIAL COMPLIANCE

Left ventricular (LV) chamber and myocardial wall compliance were investigated in rats with exercise-induced cardiac hypertrophy. Voluntary exercise training was performed on running wheels. After 16 wk of exercise training, cardiac performance was measured in anesthetized open-chest ventilated rats. LV end-diastolic performance was calculated from both short-axis external diameter and long-axis segmental length measurements. Exercise-trained rats developed significant LV hypertrophy (1.03 +/- 0.02 g) compared with control rats (0.91 +/- 0.03 g; P < 0.01). The physiological hypertrophy was associated with an increased LV wall thickness-to-internal radius ratio consistent with a concentric geometry. LV end-diastolic stiffness (slope of the linearized LV end-diastolic pressure-strain relationship) was decreased in both the short (P < 0.02) and long (P < 0.02) axis of LV as a result of exercise training. The LV end-diastolic chamber stiffness (slope of the linearized LV end-diastolic pressure-volume relationship) was also decreased in the exercised group (P < 0.05). The decreased chamber stiffness occurred as a consequence of a decrease in the regional myocardial wall elastic stiffness (slope of the linearized LV end-diastolic stress-strain relationship; P < 0.05). Thus an increased LV wall thickness as a result of exercise-induced LV hypertrophy is associated with an enhanced ventricular chamber compliance, which in turn is attributed to a decrease in the diastolic stiffness of the myocardial wall.