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What is Which of the following is a better predictor of vagal tone? and explain in detail?
Ref: Pal GK. Functional anatomy and innervation of Heart. In: Textbook of medical physiology. 2nd ed. Abuja Publishing House. 2011; 69: 578-579.Explanation:In the given options, all are influenced by sympathetic and parasympathetic activityRight vagus mainly innervates SA node, right atrium and left vagus innervates left atrium, AV node, bundle of His. But vagal innervation of ventricle is sparse. Hence, vagal stimulation strongly inhibits heart rate (strong - negative chronotropic effect) and poorly affects force of contraction (weak - negative inotropic effect).Moreover, vagus dominates sympathetic nerve in controlling SA node activity at rest. Therefore, basal heart rate mainly depends on the vagal tone.Ejection fraction, stroke volume, LVET (Left Ventricular Ejection Time) are mainly influenced by sympathetic stimulation as vagus has weaker inotropic effect