LEFT-VENTRICLE HEMODYNAMICS AND VASOACTIVE HORMONES DURING GRADED SUPINE EXERCISE IN HEALTHY MALE-SUBJECTS

Left ventricle systolic and diastolic functional parameters were measu red by gated equilibrium radionuclide cardiography in 12 healthy men ( age 33-51 years) at rest and during graded supine exercise. The left v entricle end-diastolic volume showed an initial small (11%) increase d uring low submaximal exercise [from mean 163 (SD 40) at rest to mean 1 81 (SD 48) ml], while left ventricle end-systolic volume decreased suc cessively [from mean 59 (SD 19) to mean 39 (SD 21) ml] with increasing exercise. Stroke volume was therefore elevated at all exercise levels compared with rest [mean 104 (SD 23) ml], and the peak value [mean 12 8 (SD 33) ml] was found at the lowest exercise level, contributing 40% to the initial increase in cardiac output. Cardiac output increased f rom mean 6.2 (SD 1.4) at rest to mean 20.2 (SD 5.0) l . min(-1) at max imum. Left ventricle peak ejection and peak filling rates increased fr om mean 449 (SD 89) and mean 442 (SD 85) ml . s(-1) at rest to mean 99 6 (SD 227) and mean 1255 (SD 333) ml . s(-1) respectively, at maximum. The myocardium oxygen consumption, assumed to be proportional to the sum of the stroke work and the potential energy, increased fourfold, b ut absolute values were twice as high as expected, indicating that ext rapolation from data obtained in dog hearts (as we have done) cannot b e directly applied to humans. Selected vase-active hormones were measu red at all exercise intensities. Noradrenaline (NA), adrenaline (A) an d angiotensin II (AII) concentrations showed a very pronounced increas e at maximal exercise compared with the preceding lower intensites, wh ile atrial natriuretic factor (ANF) and cyclic guanosinemonophosphate (cGMP) concentrations showed a more continuous increase, and dopamine (DA) remained almost unchanged. This speaks in favour of a crucial rol e for NA, A and AII in preserving blood pressure at maximum exercise, while DA probably has no importance for the cardiovascular homeostasis during exercise. Increases in concentrations of ANF and cGMP were hig hly correlated (r = 0.86). Our data supported the opinion that there i s a cardiac limitation to maximal performance connected to the cardiac pumping capacity.