Fainting precipitated by collapse-firing of venous baroreceptors.
I propose that fainting (vaso-vagal syncope) is caused by the sudden invagination of the walls of underfilled atria and great veins when their intraluminal pressure no longer exceeds intrathoracic pressure, leading to anomalous collapse-firing of veno-atrial stretch receptors. Impulses therefrom cause reflex systemic vasodilation and bradycardia, probably through a brainstem relay path involving opioids and possibly the A5 area of the medulla. The inappropriate increase of afferent atriovenous baroreceptor-nerve activity leads, by a vicious circle, to a sudden collapse of systemic arterial pressure. Activation of ventricular receptors is neither a probable nor a necessary cause of syncope, though it might be part of the response.
Dickinson
C J
CJ
Wolfson Institute of Preventive Medicine, St Bartholomew's Hospital Medical College, London, UK.
D000818:Animals; D006801:Humans; D011311:Pressoreceptors / Q000502:physiology*; D013575:Syncope / Q000209:etiology* / Q000503:physiopathology; D014630:Vagus Nerve / Q000502:physiology