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Influence of age and hemodynamics on myocardial blood flow and flow reserve
1Department of Radiological Sciences, UCLA School of Medicine 90024-1721.
Insights
Aging increases resting myocardial blood flow and cardiac work, reducing myocardial flow reserve. This decline is not due to impaired coronary vasodilator capacity but rather to increased baseline cardiac workload.
Area of Science:
- Cardiology
- Gerontology
- Physiology
Background:
- Aging is linked to changes in systolic blood pressure, potentially increasing cardiac work and resting myocardial blood flow.
- These changes may reduce myocardial flow reserve, mimicking age-related coronary vasodilator capacity impairment.
Purpose of the Study:
- To investigate the impact of aging on myocardial blood flow and coronary vasodilator function.
- To determine if reduced myocardial flow reserve in older adults is due to impaired vasodilation or increased resting cardiac workload.
Main Methods:
- Quantified myocardial blood flow at rest and during dipyridamole-induced hyperemia using 13N-ammonia and positron emission tomography in 40 healthy volunteers.
- Volunteers were divided into two groups: <50 years and >50 years.
Main Results:
- Older volunteers exhibited higher resting blood pressure-rate product and resting myocardial blood flow compared to younger volunteers.
- Hyperemic myocardial blood flow did not differ significantly between groups, but minimal coronary resistance was higher in older subjects.
- The myocardial flow reserve was significantly lower in older subjects (3.0 +/- 0.70) compared to younger subjects (4.1 +/- 0.9).
Conclusions:
- Aging does not significantly alter dipyridamole-induced hyperemic flows, suggesting preserved coronary vasodilator capacity.
- The reduced myocardial flow reserve in older adults is primarily attributed to increased resting cardiac work and blood flow, not impaired vasodilation.
- The findings indicate that age-related decline in flow reserve is a consequence of increased baseline myocardial workload.
Background:
Aging is associated with changes of the systolic blood pressure that may increase cardiac work and myocardial blood flow at rest and reduce the myocardial flow reserve. This might be misinterpreted as age-related impairment of the coronary vasodilator capacity.
Methods And Results:
Myocardial blood flow was quantified at rest and after administration of intravenous dipyridamole in 40 healthy volunteers (12 women and 28 men) with 13N-ammonia and positron emission tomography. Eighteen of the normal subjects were less than and 22 were older than 50 years (31 +/- 9 versus 64 +/- 9 years). The resting rate-pressure product was lower in the younger than in the older subjects (6895 +/- 1070 versus 8634 +/- 1890; P < 0.01). Myocardial blood flow at rest averaged 0.76 +/- 0.17 mL.min-1.g-1 in the younger volunteers and 0.92 +/- 0.25 mL.min-1.g-1 in the older volunteers (P < 0.05). Hyperemic blood flows did not differ between younger and older subjects (3.0 +/- 0.8 versus 2.7 +/- 0.6 mL.min-1.g-1; P = NS); however, minimal coronary resistance was higher in the older subjects. Corrected for indexes of coronary driving pressure, hyperemic flow was lower in older than in younger normal subjects. The higher resting blood flows combined with similar hyperemic flows resulted in a lower myocardial flow reserve in the older than in the younger normal subjects (4.1 +/- 0.9 versus 3.0 +/- 0.70; P < 0.0001). The flow reserve was more closely correlated with resting than with hyperemic blood flows.
Conclusions:
Aging does not alter significantly dipyridamole-induced hyperemic flows; although coronary vascular resistance after dipyridamole was somewhat increased in older subjects. The gradual decline of the myocardial blood flow reserve correlates with an age-related increase of baseline myocardial work and blood flow. These findings suggest that the reduced flow reserve with age is primarily due to increased cardiac work and blood flow at rest rather than to an abnormal vasodilator capacity.