The effects of exercise and subject age on pulsed Doppler measurements of left ventricular ejection in normal man

Pulsed Doppler measurements of ascending aortic blood velocity and acceleration were made in a group of normal subjects on exercise. The aims of the study were: (1) to document the normal response to exercise and its variability at various ages as a baseline for future studies in abnormal subjects, and (2) to investigate the accuracy and reproducibility of these noninvasive measurements. Doppler measurements were related to oxygen consumption in normal subjects aged between 22 and 69 years, during a submaximal 4 min incremental cycle exercise protocol. Computer-aided ensemble averaging of digital spectral data was used to reduce the effects of noise and respiratory variations in the signals. The mean relationship between cardiac output (Q) and oxygen consumption (Vo2) was Q = 5.75 Vo2 + 4.22 1 min-1, r = 0.84 in subjects aged under 45 years, compared to Q = 6.16 Vo2 + 3.87 1 min-1, r = 0.65 in older subjects; this difference was not significant. These values are similar to those previously described in invasive studies. There was a wide range of individual responses especially in the older subjects. These inter-subject differences probably reflect true physiological differences between subjects rather than methodological errors because they were consistent on repeated testing in the same individual, similar differences occurred in heart-rate responses between individuals where Doppler errors do not apply, and inter-subject variability of similar magnitude was found in comparable studies using invasive methods. Peak velocity (PV) rose from 73 +/- 10 cm s-1 at a Vo2 of 0.4 1 min-1 to 101 +/- 11 cm s-1 at a Vo2 of 1.21 min-1 in subjects aged under 45 years; corresponding values in the older subjects were significantly lower at 48 +/- 12 and 64 +/- 10 cm s-1 respectively. Maximum acceleration was also significantly higher at rest and on exercise in subjects under 45 years compared to older subjects. Despite these differences, stroke volume and cardiac output responses showed no significant age dependence, suggesting that differences in ejection velocity are due to increasing aortic cross-sectional area with age. The wide variety of individual responses found suggests an underlying variability in the arteriovenous oxygen difference on exercise between subjects.