Cardiovascular responses to submaximal arm and leg exercise in cardiac transplant patients.

We examined whether an increase in stroke volume (SV) contributes to the increase in cardiac output that occurs when cardiac transplant patients (CT) exercise between 50% and 75% of maximum. Upright arm and leg exercise was performed by 13 CT and 10 normal controls. Cardiac output (CO2 rebreathing), expired air, and catecholamine measures were obtained at rest and at 50% and 75% of maximum. From rest to 50% of maximum both normals and CT increased heart rate (HR) and SV during arm and leg exercise. In normals, HR (arm = +17 +/- 2 min-1; leg = +21 +/- 3 min-1) was increased further at 75% of maximum but not SV (arm = 3 +/- 4 ml; leg = +2 +/- 8 ml). In CT, further increases in both HR (arm = +9 +/- 1 min-1; leg = +13 +/- 1 min-1) and SV (arm = +12 +/- 5 ml; leg = +12 +/- 3 ml) were observed at 75% of maximum. During leg exercise plasma norepinephrine was increased more in CT than in normals. Between 50% and 75% of maximum, an increase in SV is a more important mechanism for increasing cardiac output during upright arm and leg exercise in CT than in normals.