SYMPATHOVAGAL BALANCE OF THE HEART IN SUBJECTS WITH SPINAL-CORD INJURY

This study investigated the effect of abnormal autonomic cardiovascula r function on heart rate variability (HRV) in individuals classified i nto four groups: complete quadriplegia, incomplete quadriplegia, low p araplegia, and non-spinal cord injury (SCI) controls. Measurements wer e collected at baseline and during provocative maneuvers. Spectral ana lysis using a fast-Fourier transform algorithm revealed two spectral c omponents of HRV, termed low frequency (LF) and high frequency (HF); t he LF-to-HF ratio (estimate of sympathovagal balance) was also calcula ted. Each group of subjects with quadriplegia exhibited significantly lower spectral components for both baseline and composite provocative measures compared with the non-SCI controls (P < 0.05). In addition, t he group with paraplegia demonstrated significantly lower HF baseline and LF composite levels than controls (P < 0.05). No differences were observed among all groups for the LF-to-HF ratio. This consistency in the LF-to-HF ratio suggests that the two autonomic divisions that regu late the cardiovascular system maintain homeostasis even when one comp onent is severely compromised. This is supported by the additional fin dings of decreased parasympathetic activity in the two groups with qua driplegia and the absence of significant differences among any of the four groups at rest in either heart rate or blood pressure.