Pathophysiological basis of orthostatic hypotension in autonomic failure

In patients with autonomic failure orthostatic hypotension results from an impaired capacity to increase vascular resistance during standing. This fun damental defect leads to increased downward pooling of venous blood and a c onsequent reduction in stroke volume and cardiac output that exaggerates th e orthostatic fall in blood pressure. The location of excessive venous bloo d pooling has not been established so far, but present data suggest that th e abdominal compartment and perhaps leg skin vasculature are the most likel y candidates. To improve the orthostatic tolerance in patients with autonom ic failure, protective measures ;hat reduce excessive orthostatic blood poo ling have been dec-eloped and evaluated. These measures include physical co unter-manoeuvres and abdominal compression.