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Influence of the force-frequency relation on left ventricular function during exercise in conscious dogs
T Miura1, S Miyazaki, B D Guth
1Yamaguchi University, Japan.
Circulation
|August 11, 1992
Summary
Exercise significantly enhances the force-frequency effect on myocardial contractility in conscious animals. Slowing heart rate during exercise reduces contractility, indicating a pronounced negative inotropic influence.
Area of Science:
- Cardiovascular Physiology
- Exercise Physiology
Background:
- The force-frequency effect on myocardial contractility is well-studied at rest.
- Its impact during exercise in conscious animals remains largely unassessed.
Purpose of the Study:
- To evaluate the force-frequency effect on myocardial contractility during exercise in conscious dogs.
- To determine if exercise alters the inotropic state's response to heart rate changes.
Main Methods:
- Eight conscious dogs were instrumented for left ventricular (LV) pressure and volume, and aortic pressure measurements.
- Treadmill exercise was performed, with heart rate (HR) manipulated using a bradycardic drug and atrial pacing.
- LV contractility and relaxation parameters were assessed at varying HRs during exercise.
Main Results:
- Slowing the exercise HR from 240 to 150 beats per minute significantly reduced LV contractility.
- Measures like LV maximum positive dP/dt and (dP/dt)DP40 decreased, while ventricular relaxation (tau) prolonged.
- Beat-averaged end-systolic pressure-volume points shifted downward and rightward with reduced HR.
Conclusions:
- Exercise markedly enhances the force-frequency effect on the inotropic state of the intact left ventricle.
- Slowing the heart rate during exercise exerts a pronounced negative inotropic influence.
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