Physiology Phile 001
The Valsalva Manoeuvre is an example of a tactic that demonstrates a basic cardiovascular physiologic feedback loop. The purpose of it is to induce vagal firing from the cardiovascular control centre in the medulla, in order to slow the heart rate, and interrupt the rapid ventricular rate in a supraventricular tachycardia.
The video takes us through the manoeuvre – we start with an increase in transmural pressure in the aorta, and the initial baroreceptor reflex causing an initial slowing of the heart, through afferents to the medulla and a reduction in sympathetic outflow and increased vagal firing. We then follow the fall in venous return and thus cardiac output as a result of the sustained intrathoracic pressure increase, which stimulates a reverse and increase in sympathetic outflow. When the manoeuvre finishes, after about 10 seconds, and blood rushes back into the great vessels, with added sympathetic peripheral vasoconstriction, the sudden increase in stretch at the aortic arch and carotid sinus again caused profound vagal outflow, at this point hopefully slowing down the AV node conduction enough to stop the SVT.
We then look at the best way of performing this in the clinical setting…