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Vagal stimulation decreases left ventricular contractility mainly through negative chronotropic effect
W Matsuura1, M Sugimachi, T Kawada
1Department of Cardiovascular Dynamics, National Cardiovascular Center Research Institute, Osaka, Japan.
The American Journal of Physiology
|August 11, 1997
Summary
Vagal stimulation slows heart rate (HR) and reduces left ventricular contractility. However, this study found that the reduced contractility is primarily due to the slower HR, not a direct effect on the ventricle.
Area of Science:
- Cardiology
- Autonomic Nervous System Physiology
Background:
- Vagal tone influences heart rate (HR) but its direct impact on left ventricular contractility is unclear.
- Distinguishing direct from indirect vagal effects on contractility is crucial.
Purpose of the Study:
- To determine if vagal stimulation depresses left ventricular contractility independently of its heart rate-slowing (bradycardic) effect.
- To separate direct and indirect vagal effects on ventricular contractility.
Main Methods:
- Anesthetized, sympathectomized open-chest rabbits were used.
- Left ventricular contractility was measured using end-systolic elastance (Ees).
- Vagal stimulation was applied at varying frequencies (0, 5, 10 Hz) with and without atrial pacing to maintain constant HR.
Main Results:
- Vagal stimulation dose-dependently decreased both HR and Ees.
- When HR was maintained constant via atrial pacing, vagal stimulation caused minimal change in Ees.
- This suggests minimal direct negative inotropic effect of vagal stimulation.
Conclusions:
- The negative inotropic effect of vagal stimulation is mainly attributed to its negative chronotropic effect (slowing HR).
- Direct depression of left ventricular contractility by vagal stimulation is minimal when sympathetic tone is low.