Answer 1

Vagal Escape is ,One of the most classical example of Sympathetic nervous system and Parasympathetic nervous system which can offset each other. Vagal escape is characterized by a reduction in blood pressure due to muscarinic stimulation which is then compensated for stimulation from the sympathetic system to increase heart rate and thus blood pressure.

It is generally believed that the stimulation of vagus nerve has no direct effect on ventricular myocardium. But recent work has demonstrated clear-cut negative inotropic effect of vagal stimulation on ventricles. In an attempt to study further the effect of vagal stimulation on heart, 15 dogs were studied hemodynamically under nembutal anaesthesia. Bilateral vagotomy caused 9% elevation of heart rate whereas arterial pressure and cardiac output increased by 5% and 3% respectively. Stroke volume output decreased by 8%. Stimulation of the cut peripheral end of vagus caused cardiac standstill followed by vagus escape.

Answer 2

Here is a flow chart for both the vagus escape and the mechanisms involved:

Continuous vagal stimulation --> Heart beat stops --> Vagal stimulation still continued --> Heart beat resumes

1. Idioventricular rhythm: Since, ventricles are not supplied by vagus; Purkinje-His system can act as pacemaker when vagal stimulation inhibits SA and AV node

2. Baroreflex: Heart stopped --> Decreased BP --> Stimulation of VMC --> Sympathetic stimulation

3. Bainbridge reflex: Heart stopped --> Blood accumulates --> Stimulation of atrial stretch receptors --> Stimulation of VMC --> Sympathetic stimulation