SPECTRAL ANALYSIS OF HEART RATE VARIABILITY IN PATIENTS WITH SPINAL CORD INJURY

BACKGROUND: Yearly, 200-300 new spinal cord injuries (SCI) happen in the Czech Republic. Some of these patients suffer from autonomic disturbances, especially concerning their cardiovascular and genito-urinary systems. Autonomic disturbances markedly decrease quality of life in patients with SCI. It is important to assess the severity of the autonomic nervous system (ANS) involvement in these subjects. OBJECTIVE: The main aim of this study was to assess the spectral analysis of heart rate variability as a marker of cardiovascular autonomic regulation in patients with spinal cord injury and to compare it with findings in healthy controls. METHODS: Ten paraplegics (with a mean age of 53.1 +/- 15.8 years, seven males and three females) participated in this study. There were five patients with incomplete and five patients with complete spinal cord injury. The ASIA-American Spinal Injury Association, the modified Ashworth scale and the Questionnaire on Autonomic Functions were used. Autonomic reactivity was evaluated by means of the spectral analysis of heart rate variability (SAHRV) method (short-term registration) using the supine-sitting-supine test. Diagnostic system VarCor PF7, which is an in novation of the VarCor PF6 system, was used. Twenty four healthy subjects (with a mean age of 51.9 +/- 9.4 years) were enrolled as a control group. RESULTS: A marked decrease of the reactivity of the autonomic nervous system as a response to orthostatic changes was found in patients after SCI (paraplegics). In particular, characteristic responses of low frequency (LF) and high frequency (HF) spectral components during the body position changes were suppressed in these patients in comparison with healthy controls. Furthermore, a significant decrease in the spectral power of the LF and HF components was found in patients after SCI. The value of the spectrum's total power (TP) was significantly lower in the group of paraplegics in comparison with healthy volunteers, both in the first and in the repeated supine positions. A significant degree of orthostatic hypotension was registered only in two paraplegics in a sitting position. A lower increase in the LF/HF ratio was registered in a sitting position in a group of paraplegics in comparison with healthy subjects. CONCLUSIONS: A decrease in the reactivity of the autonomic nervous system to orthostatic changes, which evidences disturbances of cardiovascular regulation, was found in patients after spinal cord injury (paraplegics). The reduction of the low-frequency component (LF) of the spectral analysis of heart rate variability reflects a lowered sympathetic activity in these patients in a sitting position. It reflects ortostatic disturbances in situations with body position changes associated with a modified orthostatic load. Blood pressure measurement and SAHRV contribute to a more precise assessment of the autonomic dysfunction in patients after SCI.