title: Incidence and hemodynamic characteristics of near-fainting in healthy 6- to 16-year old subjects.
abstract: OBJECTIVE
  We studied the incidence and hemodynamic characteristics of near-fainting under orthostatic stress in healthy children and teenagers.
  
  
  BACKGROUND
  Orthostatic stress testing is increasingly used to identify young subjects with unexplained syncope. However, the associated incidence of syncope and hemodynamic responses in normal young subjects are not well known.
  
  
  METHODS
  Eighty-four healthy subjects 6 to 16 years old performed forced breathing, stand-up and 70 degrees tilt-up tests. An intravenous line to sample blood for biochemical assessment of sympathetic function was introduced between the stand-up and tilt-up tests. Finger arterial pressure was measured continuously. Left ventricular stroke volume was computed from the pressure pulsations.
  
  
  RESULTS
  Sixteen of the 84 subjects were excluded because of technical problems. The incidence of a near-fainting response in the remaining 68 subjects was 10% (7 of 68) for the stand-up test and 40% (29 of 68) for the tilt-up test. Baseline parasympathetic and sympathetic activity of nonfainting and near-fainting subjects was not different. Near-fainting was characterized by attenuated systemic vasoconstriction and exaggerated tachycardia that occurred as early as 1 min after return to the upright position. On tilt-up, plasma adrenaline levels increased by a factor of 2, with slightly higher increments in the near-fainting subjects.
  
  
  CONCLUSIONS
  Inadequate vasoconstriction is the common underlying mechanism of near-fainting in young subjects. The remarkably high incidence of near-fainting during the tilt-up test after intravascular instrumentation raises serious doubts about the utility of this procedure in evaluating syncope of unknown origin in young subjects.
authors.affiliation: University Hospital for Children and Youth, Het Wilhelmina Kinderziekenhuis, Utrecht, The Netherlands.
authors.forename: C C
authors.initials: CC
authors.lastname: de Jong-de Vos van Steenwijk
authors.forename: W
authors.initials: W
authors.lastname: Wieling
authors.forename: J M
authors.initials: JM
authors.lastname: Johannes
authors.forename: M P
authors.initials: MP
authors.lastname: Harms
authors.forename: W
authors.initials: W
authors.lastname: Kuis
authors.forename: K H
authors.initials: KH
authors.lastname: Wesseling
mesh_terms: D000293:Adolescent; D001815:Bloodletting; D002648:Child; D004837:Epinephrine / Q000097:blood; D005189:False Positive Reactions; D005260:Female; D006439:Hemodynamics / Q000502:physiology*; D006801:Humans; D007024:Hypotension, Orthostatic / Q000503:physiopathology; D015994:Incidence; D008297:Male; D009638:Norepinephrine / Q000097:blood; D013564:Sympathetic Nervous System / Q000502:physiology; D013575:Syncope / Q000453:epidemiology* / Q000209:etiology / Q000503:physiopathology*; D018667:Tilt-Table Test / Q000706:statistics & numerical data; D013997:Time Factors; D014661:Vasoconstriction / Q000502:physiology*
chemical_list: D009638:Norepinephrine; D004837:Epinephrine