title: The effect of orthostatic stress type on cardiovascular control.
abstract: OBJECTIVE
  We aimed to compare the cardiovascular responses of a novel orthostatic stress test, the passive seated orthostatic stress test (PSOST), with those during passive head-up tilt testing (HUTT). We hypothesized that cardiovascular responses during PSOST would be similar to those during HUTT (the 'gold standard').
  
  
  METHODS
  We tested 15 healthy volunteers, who underwent both PSOST and HUTT during one session in a random order. We measured beat-to-beat blood pressure, heart rate, peripheral resistance, stroke volume, cardiac output, and middle cerebral artery blood flow velocity during each test.
  
  
  RESULTS
  Blood pressure responses were not significantly different between PSOST and HUTT, except for a significantly lower delayed nadir and 15-min recovery value in systolic arterial pressure during HUTT. HUTT elicited a significantly larger increase in heart rate during all test intervals in comparison with PSOST, as well as a larger decline in stroke volume during almost all test intervals. Responses for the other hemodynamic variables were not significantly different between the tests at any test interval. Repeated HUTT has large inherent variability, which was also evident from the variability in the mean differences on comparing PSOST and HUTT. There was a significant bias for larger heart rate increases (P<0.01) and a greater delayed systolic arterial pressure decline during HUTT.
  
  
  CONCLUSIONS
  We have shown that PSOST and HUTT elicit similar blood pressure and cerebrovascular responses in the early stages of the upright phase. We believe that PSOST is a reasonable surrogate for HUTT in assessing orthostatic hypotension in population groups that are unable to stand for prolonged periods of time.
authors.affiliation: Departments of aBiomedical Physiology and Kinesiology bStatistics and Actuarial Sciences, Simon Fraser University cCentre for Hip Health and Mobility, Vancouver Coastal Health Research Institute, British Columbia, Canada.
authors.forename: Brett H
authors.initials: BH
authors.lastname: Shaw
authors.forename: Thomas M
authors.initials: TM
authors.lastname: Loughin
authors.forename: Dawn C
authors.initials: DC
authors.lastname: Mackey
authors.forename: Stephen N
authors.initials: SN
authors.lastname: Robinovitch
authors.forename: Victoria E
authors.initials: VE
authors.lastname: Claydon
mesh_terms: D000328:Adult; D001783:Blood Flow Velocity; D001794:Blood Pressure; D004244:Dizziness / Q000503:physiopathology*; D005260:Female; D006801:Humans; D008297:Male; D020768:Middle Cerebral Artery / Q000503:physiopathology*; D011187:Posture; D013315:Stress, Psychological / Q000503:physiopathology*; D013318:Stroke Volume