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Postural changes in cardiac volumes in men in relation to adult age
Insights
Healthy older adults rely more on the Frank-Starling mechanism than heart rate for cardiac output adjustments. This indicates a greater reliance on stroke volume changes to maintain cardiac output when changing posture.
Area of Science:
- Cardiovascular Physiology
- Geriatric Cardiology
Background:
- Cardiac output regulation is crucial for maintaining blood pressure and organ perfusion.
- Aging affects cardiovascular responses to postural changes, impacting cardiac volumes and heart rate.
Purpose of the Study:
- To investigate age-related differences in cardiac output regulation during postural changes.
- To determine the compensatory mechanisms (heart rate vs. stroke volume) involved in maintaining cardiac output in healthy older adults.
Main Methods:
- Equilibrium gated cardiac blood pool scans were used to measure cardiac volumes.
- Heart rate and cardiac volumes were measured in supine and sitting positions in 64 healthy male subjects (aged 25-80).
- Linear regression analysis examined the relationship between postural changes in cardiac output, heart rate, and stroke volume across age groups.
Main Results:
- Average cardiac output remained unchanged with postural change, but heart rate increased and stroke volume decreased due to reduced end-diastolic volume.
- Individual postural changes in cardiac output correlated with stroke volume changes in all age groups, and heart rate changes in younger subjects.
- The correlation between cardiac output change and stroke volume change was stronger in older adults, indicating a greater reliance on stroke volume.
Conclusions:
- While average cardiac output is not age-related with postural changes, individual responses vary.
- Older adults exhibit a greater dependence on stroke volume (Frank-Starling mechanism) than heart rate for maintaining cardiac output during postural transitions.
- This suggests a shift in cardiovascular regulatory strategies with aging, prioritizing stroke volume adjustments over heart rate acceleration.
Abstract:
Cardiac volumes by equilibrium gated cardiac blood pool scans and heart rate were measured in the supine and sitting positions in 64 male volunteer subjects (age 25-80 yrs) who had been rigorously screened to exclude cardiovascular disease. After the upright position was assumed, the average cardiac output of all subjects was unchanged but heart rate increased and stroke volume decreased due to a decrease in end diastolic volume. Neither the supine or sitting cardiac output nor the average postural change in cardiac output, cardiac volumes or heart rate was age-related. While the average cardiac output among the subjects was unaltered with a change in posture, in some individuals it increased slightly while in others it decreased. The postural change in cardiac output among the individuals correlated by linear regression analysis with a change in heart rate only in younger subjects and with a change in stroke volume in all age groups, but the slope of this relationship was greater in older than in younger subjects. The postural change in stroke volume was strongly correlated with a change in end diastolic volume and this relationship did not vary with age. Thus, although the average postural change in cardiac output among healthy subjects is not age-related, a given change in cardiac output with posture in an older individual depends more on a change in stroke volume and less on a heart rate change than in a younger one. This result, like the response to vigorous upright exercise previously demonstrated to occur with aging, indicates a greater reliance in the elderly on the Frank-Starling mechanism than on heart rate for a given change in cardiac output in response to perturbations from the basal supine state.