title: What is the minimum duration of head-up tilt necessary to detect orthostatic hypotension?
abstract: OBJECTIVE
  There is uncertainty as to the minimum duration of head-up tilt (HUT) needed to detect orthostatic hypotension (OH). The orthostatic duration has variably been recommended to be 1, 2, 3, and 5 minutes. The purpose of the current study was 1) to determine the minimum duration of HUT necessary to detect OH and 2) to identify different patterns of orthostatic blood pressure (BP) response in patients with OH.
  
  
  METHODS
  We evaluated the medical records of 66 consecutive patients (mean age 70.0+/-10.1 years; 64% male) seen at Mayo Clinic-Rochester from 2000-2001 who fulfilled the criteria for OH (systolic blood pressure [SBP] reduction > or = 20 mmHg within 3 minutes of HUT) during routine clinical autonomic studies. All patients completed an autonomic reflex screen with continuous monitoring of heart rate and BP during supine rest and 5 minutes of 70 degree HUT. Severity of autonomic deficits was quantified with the Composite Autonomic Severity Score (CASS).
  
  
  RESULTS
  Overall, BP was the lowest at 1 minute with gradual and partial recovery over the following 4 minutes. Eighty-eight percent of patients (N=58) developed OH by 1 minute of HUT, with an additional 11% (N=7) developing OH by 2 minutes and the remaining 1% (N=1) developing OH by 3 minutes. We identified two broad patterns of SBP response to HUT. Forty-eight percent (N=32) of patients demonstrated an initial drop in SBP (> or = 20 mm Hg),which remained stable until tilt-back. Thirty-six percent (N=24) demonstrated an initial drop (> or = 20 mmHg) followed by a progressive decline in SBP until tilt-back. Repeated measures analysis of variance confirmed that the SBP change in response to HUT differed significantly among patients with a stable vs. progressive pattern [F(3,32)=25.1, p<0.001). Patients with the progressive pattern also had more severe adrenergic impairment on the CASS (p=0.03) and were more likely to have their tilt test terminated early (prior to 5 minutes) due to presyncope (p<0.0001) than patients with the stable pattern.
  
  
  CONCLUSIONS
  One minute of HUT will detect OH in the great majority (88%) of patients and three minutes will detect the balance. Orthostatic stress beyond 2 minutes is necessary to detect the pattern of progressive OH. Since this group has more severe adrenergic deficits than the group with stable OH, we suggest that the progressive pattern is due to greater impairment of compensatory reflexes. Recognition of the group with progressive fall in BP is important since this group may be at greater risk of orthostatic syncope.
authors.affiliation: Dept. of Neurology, Mayo Clinic, Rochester (MN) 55905, USA.
authors.forename: Jade A
authors.initials: JA
authors.lastname: Gehrking
authors.forename: Stacy M
authors.initials: SM
authors.lastname: Hines
authors.forename: Lisa M
authors.initials: LM
authors.lastname: Benrud-Larson
authors.forename: Tonette L
authors.initials: TL
authors.lastname: Opher-Gehrking
authors.forename: Phillip A
authors.initials: PA
authors.lastname: Low
mesh_terms: D000368:Aged; D001341:Autonomic Nervous System / Q000503:physiopathology; D017704:Baroreflex / Q000502:physiology; D001794:Blood Pressure / Q000502:physiology; D005260:Female; D006801:Humans; D007024:Hypotension, Orthostatic / Q000175:diagnosis* / Q000503:physiopathology; D008297:Male; D011187:Posture / Q000502:physiology*; D013997:Time Factors