Regulation of myocardial blood flow by oxygen consumption is maintained in the failing heart during exercise
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J H Traverse1, P Melchert, G L Pierpont
1Cardiovascular Division, Department of Medicine, University of Minnesota Medical School, Minneapolis, USA.
Insights
Congestive heart failure (CHF) reduces myocardial oxygen consumption and coronary blood flow during exercise. Despite impaired blood flow, the heart did not show signs of ischemia, suggesting reduced oxygen usage in heart failure.
Area of Science:
- Cardiovascular Physiology
- Heart Failure Pathophysiology
Background:
- Congestive heart failure (CHF) involves hemodynamic changes and neurohumoral activation.
- These changes may impair the normal increase in coronary blood flow during physical activity.
Purpose of the Study:
- To investigate the impact of CHF on myocardial oxygen consumption.
- To assess coronary blood flow dynamics during exercise in the presence of CHF.
Main Methods:
- Coronary blood flow was measured in dogs at rest and during two stages of treadmill exercise.
- Measurements were taken under control conditions and after inducing CHF via rapid ventricular pacing.
Main Results:
- CHF dogs exhibited 25% lower resting myocardial blood flow compared to controls.
- During exercise, coronary blood flow increased initially but failed to rise further in CHF dogs despite increased cardiac workload (RPP).
- Myocardial oxygen consumption was lower in CHF dogs and paralleled coronary flow, without evidence of ischemia.
Conclusions:
- CHF is associated with reduced myocardial oxygen consumption and an inability to increase it with exercise.
- This impairment appears to stem from decreased oxygen utilization rather than insufficient oxygen supply.
- The findings suggest a reduction in metabolic coronary vasodilation in heart failure.
Abstract:
The hemodynamic abnormalities and neurohumoral activation that accompany congestive heart failure (CHF) might be expected to impair the increase in coronary blood flow that occurs during exercise. This study was performed to determine the effects of CHF on myocardial oxygen consumption and coronary blood flow during exercise. Coronary blood flow was measured in chronically instrumented dogs at rest, during 2 stages of graded treadmill exercise under control conditions (n=10), and after the development of CHF produced by 3 weeks of rapid ventricular pacing (n=9). In the normal dogs, coronary blood flow increased during exercise in proportion to the increase in the heart rate x the left ventricular systolic blood pressure product (RPP). After the development of CHF, resting myocardial blood flow was 25% lower than normal (P<0.05). Myocardial blood flow increased during the first stage of exercise, but then failed to increase further during the second stage of exercise despite an additional increase in the RPP. Myocardial oxygen consumption during exercise was significantly lower in animals with CHF and paralleled coronary flow. Despite the lower values for coronary blood flow in animals with CHF, there was no evidence for myocardial ischemia. Thus, even during the second level of exercise when coronary flow failed to increase, myocardial lactate consumption continued and coronary venous pH did not fall. In addition, the failure of coronary flow to increase as the exercise level was increased from stage 1 to stage 2 was not associated with a further increase in myocardial oxygen extraction. Thus, cardiac failure was associated with decreased myocardial oxygen consumption and failure of oxygen consumption to increase with an increase in the level of exercise. This abnormality did not appear to result from inadequate oxygen availability, but more likely represented a reduction of myocardial oxygen usage with a secondary decrease in metabolic coronary vasodilation.
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