We hypothesize that local vasoconstriction is compromised in high P v POTS but baroreceptor mediated sympathetic control is not. The response to HUT supports this speculation. Leg flow increases during early orthostasis because local vasoconstriction is defective and gravitational stimulation is invoked. It is likely that if there were a defective V-A reflex, it would significantly compromise the response to orthostasis by causing increased arteriolar, capillary and venous blood pressure potentially resulting in interstitial edema. A prediction of this is enhanced acrocyanosis.
Preliminary data support the interpretation of defective venoarteriolar reflex.
After determining resting mean arterial pressure, P v , and flow, the occlusion cuff was inflated to a steady 50 mmHg to invoke the venoarteriolar reflex and flow was remeasured after 4 minutes. Decreased calf resistance occurred in 6 out of 7 high P v patients while resistance increased in normal P v patients and in controls as expected for competent venoarteriolar reflex.