Syncope Cases
Published Online: 16 Nov 2007
Editor(s): Roberto Garc�a-Civera, Gonzalo Bar�n-Esquivias, Jean-Jacques Blanc, Michele Brignole, Angel Moya i Mitjans, Ricardo Ruiz-Granell, Wouter Wieling
Print ISBN: 9781405151092 Online ISBN: 9780470995013
Copyright © 2006 by Blackwell Publishing
http://www3.interscience.wiley.com/cgi-bin/summary/116842153/SUMMARY
A mismatch between intravascular volume and the required cardiac output on standing up is the most common cause of orthostatic hypotension. In a small minority of cases, however, orthostatic hypotension is not caused by volume depletion, but by impairment of the autonomic reflexes required to maintain blood pressure in the upright position. This disorder is known as autonomic failure.
In patients with autonomic failure, orthostatic hypotension is caused by an impaired capacity of sympathetic nerves to increase vascular resistance. Downward pooling of venous blood and a consequent reduction in stroke volume and cardiac output lead to the orthostatic fall in arterial pressure.