The relation between lower limb pooling and blood flow during orthostasis in the postural orthostatic tachycardia syndrome of adolescents

OBJECTIVES: Postural orthostatic tachycardia syndrome (POTS) is characterized by symptoms of lightheadedness, fatigue, and signs of edema, acrocyanosis, and exaggerated tachycardia within 10 minutes of upright posture. Our objective was to determine how vascular properties contribute to the pathophysiology of POTS in adolescents. STUDY DESIGN: We compared 11 patients aged 13 to 18 years with 8 members of a control group, recording continuous heart rate and blood pressure and using strain-gauge plethysmography to measure forearm and calf blood flow and to estimate venous pressure while the subjects were supine. Calf blood flow and size change were measured during 70 degrees head-up tilt. RESULTS: Resting calf venous pressure was higher in the POTS group compared with the control group. Resting resistance was decreased in both the forearm (15 +/- 2 vs 30 +/- 4) and calf (27 +/- 2 vs 42 +/- 5) in the POTS group. Calf blood flow 60 seconds after tilt increased from 1.9 +/- 0.4 mL/100 mL/min to 6.6 +/- 2.3 mL/100 mL/min in the POTS group but only by half in the control group. Flow remained elevated in the POTS group but decreased to 70% baseline in the control group. Calf volume increased twice as much in the POTS group compared with the control group over a shorter time (13 vs 30 minutes). CONCLUSIONS: Lower resistance at baseline reflects a defect in arterial vasoconstriction in POTS, further exacerbated during upright posture.