Inappropriate Early Hypotension in Adolescents A Form of Chronic Orthostatic Intolerance with Defective Dependent Vasoconstriction

Instantaneous orthostatic hypotension INOH has been reported in children and adolescents as a new entity of orthostatic intolerance in children who underwent rapid standing as an orthostatic stress test. Children with INOH were discovered among patients presenting with symptoms of chronic orthostatic intolerance, which is often related to orthostatic tachycardia. We used headup tilt table testing at 70° to investigate children presenting with symptoms of chronic orthostatic intolerance. We compared 24 patients aged 1217 y, with chronic orthostatic intolerance and symptoms for =3 mo, with 13 healthy normal control patients. We recorded continuous heart rate, blood pressure, and respiratory rate and used venous occlusion strain gauge plethysmography to measure calf and forearm blood flow while supine and calf blood flow during headup tilt. Patients with chronic orthostatic intolerance fulfilled criteria for the postural orthostatic tachycardia syndrome. Postural orthostatic tachycardia syndrome patients were divided into two groups by the occurrence of INOH. Supine forearm and calf arterial resistance was decreased in patients with INOH n8 compared with postural orthostatic tachycardia syndrome patients without INOH n16 and compared with control n13. Resting calf venous pressure was elevated, suggesting excess venous filling because of vasodilation. During early headup tilt, calf blood flow increased markedly in INOH, less in NoINOH, postural orthostatic tachycardia syndrome patients and least in control patients. Flow was temporally related to calf swelling and negatively correlated to hypotension. The data suggest that INOH occurs in patients with chronic orthostatic intolerance and orthostatic tachycardia and is related to rapid caudal blood flow when upright because of a vasoconstrictor defect.