title: Relation of postural vasovagal syncope to splanchnic hypervolemia in adolescents.
abstract: 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.
  
  
  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 degrees 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.
authors.affiliation: Department of Pediatrics, The Center for Pediatric Hypotension, Suite 618, Munger Pavilion, New York Medical College, Valhalla, NY 10595, USA. stewart@nymc.edu
authors.forename: Julian M
authors.initials: JM
authors.lastname: Stewart
authors.forename: Kenneth J
authors.initials: KJ
authors.lastname: McLeod
authors.forename: Sanjukta
authors.initials: S
authors.lastname: Sanyal
authors.forename: Gilbert
authors.initials: G
authors.lastname: Herzberg
authors.forename: Leslie D
authors.initials: LD
authors.lastname: Montgomery
mesh_terms: D000293:Adolescent; D000328:Adult; D001810:Blood Volume; D002648:Child; D004244:Dizziness / Q000503:physiopathology; D005260:Female; D006439:Hemodynamics; D006801:Humans; D020896:Hypovolemia / Q000150:complications; D008297:Male; D011187:Posture; D013152:Splanchnic Circulation; D019462:Syncope, Vasovagal / Q000209:etiology* / Q000503:physiopathology; D035423:Thoracic Cavity / Q000098:blood supply