Sympathetic nervous system activity and cardiovascular homeostatis during head-up tilt in patients with spinal cord injuries.
The relationship between sympathetic nervous system activity and cardiovascular responses to head-up tilt in patients with spinal cord injuries and in able-bodied subjects was studied. Twenty-seven adults, nine in each of the three groups (tetraplegia, paraplegia, and able-bodied subjects) were tilted 70 degrees, head up, for 12 minutes after 20 minutes supine rest. Differences between steady-state measurements of mean arterial pressure, stroke volume, and sympathetic nervous system activity were estimated in both positions. Sympathetic nervous system activity was reflected by the low-frequency peak of the blood pressure variability spectrum. From supine rest to head-up tilt, low-frequency power increased in able-bodied subjects (median, 0.42 mm Hg2, p = 0.003), which was different (p = 0.015) from patients with tetraplegia and paraplegia (-0.15 and -0.10 mm Hg2, respectively). Stroke volume and mean arterial pressure decreased in patients with tetraplegia (-40% and -9 mm Hg, respectively; p = 0.008, both variables) more than in able-bodied subjects (-33%, 11 mm Hg, respectively) or patients with paraplegia (-24%, 8 mm Hg, respectively). Results indicated increased sympathetic nervous system activity during head-up tilt in able-bodied subjects, but not in patients with paraplegia or tetraplegia, whereas patients with tetraplegia, but not paraplegia, showed poorer cardiovascular homeostasis than able-bodied subjects. This suggests that patients with paraplegia maintained cardiovascular homeostasis during head-up tilt without increased sympathetic nervous system activity.
Houtman
S
S
Department of Physiology, University of Nijmegen, The Netherlands. S.Houtman@fysio.kun.nl
Oeseburg
B
B
Hughson
R L
RL
Hopman
M T
MT
D000328:Adult; D001794:Blood Pressure / Q000502:physiology; D006339:Heart Rate / Q000502:physiology; D006439:Hemodynamics / Q000502:physiology*; D006706:Homeostasis / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D010264:Paraplegia / Q000503:physiopathology; D011187:Posture / Q000502:physiology*; D011782:Quadriplegia / Q000503:physiopathology; D013119:Spinal Cord Injuries / Q000503:physiopathology*; D013318:Stroke Volume / Q000502:physiology; D016683:Supine Position / Q000502:physiology; D013564:Sympathetic Nervous System / Q000503:physiopathology*