IS A DECREASE IN ARTERIAL-PRESSURE DURING LONG-TERM AEROBIC EXERCISE CAUSED BY A FALL IN CARDIAC PUMP FUNCTION

Ten healthy normotensive, volunteers demonstrated:g progressive decrea se (p < 0.01) in systolic and diastolic pressures during 1 hour of aer obic exercise. Cardiac function and structure were assessed by M-mode echocardiography before exercise and, at the same heart rate, after 5 minutes of exercise and after 60 minutes of exercise. After 5 minutes of exercise, heart rate, cardiac output, ejection fraction, fractional fiber shortening, and contractility index significantly increased (p < 0.01, p < 0.05, respectively) and total peripheral resistance decrea sed (p < 0.01) compared with resting values. When compared with the va lues at minute 5, there was a decrease (p < 0.01) in cardiac output, e jection fraction, fractional fiber shortening, and contractility index (p < 0.05) and an increase (p < 0.05) in total peripheral resistance after 60 minutes of exercise. We conclude that the gradual decrease in arterial pressure seen with prolonged aerobic exercise is the result of a fall in cardiac pump function (as measured by cardiac output, eje ction fraction, fractional fiber shortening, and contractility index), possibly indicating cardiac fatigue.)