title: Cardiac autonomic responses to progressive head-up tilt in individuals with paraplegia.
abstract: Beat-to-beat fluctuations in heart rate are partially controlled by the autonomic nervous system and may be altered by a spinal cord injury. The purpose of the present investigation was to examine the role of the autonomic nervous system in modulating the heart rate response to head-up tilt (HUT) in subjects with low lesion paraplegia. Nineteen subjects with paraplegia and nine age-, height-, and weight-matched control subjects consented to participate. A three lead ECG was used to acquire heart rate (HR), cardiac sympathetic [low frequency component of R-R interval variability (LFRRI)], vagal [high frequency component of R-R interval variability (HFRRI)] and sympatho-vagal balance (LF/HF). A finger photoplethysmograph was used to assess beat-to-beat blood pressure for the estimation of sympathetic vasomotor tone [low frequency component of peak systolic blood pressure variability (LFSBP)]. The results showed a significant main effect for tilt angle for the HR response to HUT, which was comparable between the groups. LFRRI was significantly increased (P < 0.001) and HFRRI was significantly reduced (P < 0.001) across tilt angle in the control group, whereas subjects with paraplegia demonstrated no significant change in LFRRI, but significantly reduced HFRRI (P < 0.001) across tilt angle. There was a significant interaction effect for LF/HF (P < 0.05). LFSBP was significantly reduced in the group with paraplegia compared to controls (P < 0.05). These findings suggest that although cardiac autonomic control is intact, there is a blunted sympathetic response to HUT in subjects with low lesion paraplegia, which may implicate an altered baroreceptor response to acute orthostatic provocation.
authors.affiliation: Veterans Affairs, Medical Center SCI and Medical Services, Bronx, NY, USA. jwecht@hotmail.com
authors.forename: Jill M
authors.initials: JM
authors.lastname: Wecht
authors.forename: Ronald E
authors.initials: RE
authors.lastname: De Meersman
authors.forename: Joseph P
authors.initials: JP
authors.lastname: Weir
authors.forename: Ann M
authors.initials: AM
authors.lastname: Spungen
authors.forename: William A
authors.initials: WA
authors.lastname: Bauman
mesh_terms: D000328:Adult; D001341:Autonomic Nervous System / Q000503:physiopathology*; D016022:Case-Control Studies; D004562:Electrocardiography; D018475:Head-Down Tilt; D006321:Heart / Q000294:innervation*; D006339:Heart Rate; D006801:Humans; D008297:Male; D008875:Middle Aged; D010264:Paraplegia / Q000503:physiopathology*; D017156:Photoplethysmography; D013564:Sympathetic Nervous System / Q000503:physiopathology; D014630:Vagus Nerve / Q000503:physiopathology