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Secondary AV conduction responses during tonic vagal stimulation
The American Journal of Physiology
|October 1, 1983
Summary
Vagal stimulation affects heart rate and contractility. Secondary changes in atrioventricular (AV) conduction depend on initial response intensity, suggesting opposing mechanisms influence cardiac autonomic control.
Area of Science:
- Cardiovascular Physiology
- Autonomic Nervous System Regulation
Background:
- Vagal nerve stimulation influences cardiac function, impacting atrial contractility and atrioventricular (AV) conduction.
- Understanding the dynamic responses to vagal stimulation is crucial for comprehending cardiac autonomic control.
Purpose of the Study:
- To investigate the biphasic effects of vagal stimulation on atrial contractility and AV nodal conduction in dogs.
- To elucidate the mechanisms underlying variable secondary changes in AV conduction time following vagal stimulation.
Main Methods:
- Supramaximal vagal nerve stimulation at varying frequencies (2, 4, 8 Hz) in anesthetized, open-chest dogs.
- Simultaneous assessment of atrial contractility and AV conduction during atrial pacing.
- Analysis of initial and secondary responses to vagal stimulation.
Main Results:
- Vagal stimulation induced an initial negative inotropic effect on the atrium, followed by a secondary fading.
- Negative dromotropic responses also showed initial effects with subsequent secondary changes.
- Secondary changes in AV conduction varied from fading to augmentation, depending on the initial response magnitude.
Conclusions:
- Two opposing mechanisms likely explain the variable secondary changes in AV conduction time.
- Stimulus intensity dictates the dominance of these mechanisms, potentially involving muscarinic receptor desensitization or acetylcholine diffusion dynamics.