title: Normal HR with tilt, yet autonomic dysfunction in persons with Down syndrome.
abstract: Persons with Down syndrome (DS) exhibit altered autonomic function at rest and in response to adrenergic stimuli. It is unknown whether a subset of persons with DS that have similar HR responses to a task would have similar responses in HR variability (HRV).
  
  
  OBJECTIVE
  This study aimed to compare cardiac autonomic function during upright tilt using HRV analysis in persons with and without DS when persons with and without DS were matched for the change in HR.
  
  
  METHODS
  Persons with (25 ± 2 yr; 30.4 ± 1.9 kg·m, n = 15) and without DS (27 ± 2 yr; 24.7 ± 1.1 kg·m, n = 15) were matched on their HR response to a 5-min tilt at 80°, whereas a subset of persons with DS (28 ± 3 yr; 33.5 ± 2.0 kg·m, n = 11) were not matched for the change in HR. HRV was assessed in both the frequency (natural log transformation (Ln) of low frequency (LF), high frequency (HF), LF/HF ratio, and total power (TP)) and time domains (root mean square of successive differences [RMSSD]).
  
  
  RESULTS
  Changes in HR were similar in DS-matched and control but lower in DS-not matched. Tilt effects were observed for LnHF, LNTP, and RMSSD in all groups (P < 0.05). Both groups of persons with DS exhibited reduction in LnLF, with no change in the control group (P < 0.05). The increase in LF/HF was greater in the group without DS when compared with that in DS-not matched (8.71 ± 2.38 vs 2.34 ± 1.39, P < 0.05) but not when compared with that in DS-matched (3.59 ± 1.10, P = 0.075).
  
  
  CONCLUSIONS
  Despite similar HR response to passive upright tilt in the DS-matched, we still observed reduced sympathetic dominance in response to upright tilt in persons with DS.
authors.affiliation: 1Integrative Physiology Laboratory, Department of Kinesiology and Nutrition, University of Illinois, Chicago, IL; 2Department of Physiology, Georgia Regents University, Augusta, GA; 3Department of Health, Leisure, and Exercise Science, Appalachian State University, Boone, NC; 4Department of Nutrition, Food, and Exercise Sciences, Florida State University, Tallahassee, FL; and 5Department of Physical Therapy, Wichita State University, Wichita, KS.
authors.forename: Kanokwan
authors.initials: K
authors.lastname: Bunsawat
authors.forename: Styliani
authors.initials: S
authors.lastname: Goulopoulou
authors.forename: Scott R
authors.initials: SR
authors.lastname: Collier
authors.forename: Arturo
authors.initials: A
authors.lastname: Figueroa
authors.forename: Kenneth H
authors.initials: KH
authors.lastname: Pitetti
authors.forename: Tracy
authors.initials: T
authors.lastname: Baynard
mesh_terms: D000293:Adolescent; D000328:Adult; D015992:Body Mass Index; D004314:Down Syndrome / Q000503:physiopathology*; D005080:Exercise Test; D006339:Heart Rate; D006801:Humans; D010101:Oxygen Consumption; D010275:Parasympathetic Nervous System / Q000503:physiopathology*; D012189:Retrospective Studies; D013564:Sympathetic Nervous System / Q000503:physiopathology*; D018667:Tilt-Table Test; D055815:Young Adult