BEAT-BY-BEAT STROKE VOLUME ASSESSMENT BY PULSED DOPPLER IN UPRIGHT AND SUPINE EXERCISE

A 3.0-MHz pulsed Doppler echocardiograph was used to estimate instantaneous stroke volume (SV) and cardiac output (.ovrhdot.Q) in 8 men during steady-state supine (S) and upright (U) exercise at 300 kpm[kilopound-minute]/min. The mean transients in heart rate (HR), SV and .ovrhdot.Q for the first 20 s of exercise in each posture were then determined. Center-line blood velocities were obtained in the ascending aorta with the transducer positioned manually in the suprasternal notch. Mean supine values for SV and .ovrhdot.Q at rest and exercise were 111 ml and 6.4 l/min and 112 ml and 9.7 l/min, respectively. The corresponding results for U were 76 ml and 5.6 l/min and 92 ml and 8.4 l/min, respectively. These values compare favorably with previous studies utilizing invasive procedures. The transient response of .ovrhdot.Q following the onset of exercise in U was about twice as fast as in S because of the rapid and almost immediate upsurge in SV. In S, only HR served to augment .ovrhdot.Q, as SV initially fell. The faster rise in aortic flow in U with exercise represented an additional volume (184 ml) of blood passing through the aorta compared with S in the first 20 s. This must be related to the rapid mobilization of pooled venous blood from the leg veins during U.