The Effects of Exercise and Subject Age on Pulsed Doppler Measurements of Left Ventricular Ejection in Normal Man

Abstract

SUMMARYPulsed 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 = 575 V. +422 1 min-1, r = 0-84 in subjects aged under 45 years, compared to Q = 6-16 VO +3-87 1 min-1, r = 0-65 in older subjects; this difference was not significant. These values are slmilar 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-' at a 0Oof 0-4 1 min-' to 101 + 11 cm s-1 at a Vo of 12 1 min-' 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.

Dynamics and dimensions of cardiac output changes in humans at the onset and at the end of moderate rhythmic exercise.

“…With the good signal quality predominately achieved in the resting situation as well as during exercise, we feel that this variability does not rest with the method but must mainly reflect real physiological differences. In their study of subject age and the response to exercise using the Doppler technique, Innes, Simon, Murphy & Guz (1988) also found appreciable differences in individual responses to exercise, and they speculate that variations in the physiological condition of the subjects between tests might explain at least part of the observed variability.…”

Studies on the Circulation in Normotensive Febrile Patients

“…Peak velocity, maximal acceleration and PEP/LVET ratio showed no significant differences when febrile as compared to when afebrile and fell within their normal ranges (PV = -0 81 age+90 3 cm/s; r = --0 79. sy x = 9 19: MA = -2-2 age+2 4 m/s2; r =-0 66. sy x = 0-34; PEP/LVET = 0-35 + 0-04; Weissler & Garrard, 1971;Innes, Simon, Murphy & Guz, 1988). The PEP and LVET were significantly shortened during fever; however they were not significantly different from the values predicted for the heart rate by the regression equations described above.…”

“…There is no evidence that the methods used are insensitive to change. The principal errors are likely to lie in absolute measurement, with the source of the error being in the measurement of aortic diameter (Innes et al 1988). An absolute error of this type would not have influenced this study since the same measurement of aortic diameter was applied to both febrile and afebrile states; this assumes that, in the absence of a change in blood pressure, aortic diameter would not change within the time span of the study.…”