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(Circulation. 2004;110:2575-2581.)
© 2004 American Heart Association, Inc.

Arrhythmia/Electrophysiology

Relation of Postural Vasovagal Syncope to Splanchnic Hypervolemia in Adolescents

From the Departments of Pediatrics (J.M.S., G.H.) and Physiology (J.M.S.) and the Medical College (S.S.), New York Medical College, Valhalla, NY; the State University of New York at Binghamton (K.J.M.); and LDM Associates, San Jose, Calif (L.D.M.).

Correspondence to Julian M. Stewart, MD, PhD, Professor of Pediatrics and Physiology, The Center for Pediatric Hypotension, Suite 618, Munger Pavilion, New York Medical College, Valhalla, NY 10595. E-mail stewart{at}nymc.edu

Received February 5, 2004; revision received April 1, 2004; accepted April 7, 2004.

Background— The mechanisms of simple faint remain elusive. We propose that postural fainting is related to excessive thoracic hypovolemia and splanchnic hypervolemia during orthostasis compared with healthy subjects.

Methods and Results— We studied 34 patients 12 to 22 years old referred for multiple episodes of postural faint and 11 healthy subjects. Subjects were studied in the supine position and during upright tilt to 70° for 30 minutes and subgrouped into S+, historical fainters who fainted during testing (n=24); S–, historical fainters who did not faint during testing (n=10); and control subjects. Supine venous occlusion plethysmography showed no differences between blood flows of the forearm and calf in S+, S–, or control. Cardiac index, total peripheral resistance, and blood volume were not different. Using impedance plethysmography, we assessed blood redistribution during upright tilt. This demonstrated decreased thoracic blood volume and increased splanchnic, pelvic, and leg blood volumes for all subjects. However, thoracic blood volume was decreased in S+ compared with control volume, correlating well with the maximum upright heart rate. Splanchnic volume was decreased in the S+ and S– groups, correlating with the change in thoracic blood volume. Pelvic and leg volume changes were similar for all groups and uncorrelated to thoracic blood volume.

Conclusions— Enhanced postural thoracic hypovolemia and splanchnic hypervolemia are associated with postural simple faint.

Key Words: syncope • blood volume • hypovolemia

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