Abstract
Although in subjects with traumatic spinal cord injury (SCI) the disruption of the autonomic nervous system is well characterized, most available data refers to long-established lesions. Whether the reduction of autonomic cardiovascular control following SCI is time-independent or time-variant is still unclear. PURPOSE: To assess autonomic function in recent SCI patients, compared to long-term SCI and able-bodied subjects. METHODS: Nine patients with recent SCI (6 males; 27+12 [m+DS] years; lesion level C6-L1, lesion duration < 3 months), 9 patients with established SCI (7 males; 29+6 years, lesion level C6-L1, lesion duration > 4 years) and 16 age- and sex-matched control subjects (12 males; 27+2 years) were enrolled. Heart rate (HR) was monitored in each subject on a beat-to-beat basis for 10 minutes in supine position by means of a HR monitor. HR, time domain (RMSSD [route mean square of successive differences]) and frequency domain (LF [Low Frequency: 0,04-0,15 Hz] and HF [High Frequency: 0,15–0,40 Hz] normalized powers, LF/HF ratio) indexes of heart rate variability (HRV) were assessed from each beat-to-beat series. RESULTS: HR (67+13 vs. 74+13 vs. 73+11 bpm, in recent SCI, long-term SCI and able-bodied subjects, respectively) and RMSSD (44.6+19.2 vs. 35.1+12.2 vs. 42.3+9.3 ms) did not significantly differ between groups (1-way ANOVA, p=ns). LF [normalized units](64.2+13.1 vs. 75.8+8.7 vs. 80.4+7.0, p<0.05), and HF (35.8+13.1 vs. 24.2+8.7 vs. 19.6+7.0, p<0.05) powers and LF/HF (2.4+1.5 vs. 3.8+2.7 vs. 4.7+1.9, p<0.05) significantly differed between recent, established SCI patients and able bodied subjects. Furthermore, in recent SCI subjects HR significantly correlated with the lesion level (r2=0.66, p<0.05); conversely, such relationship was lost in established SCI subjects. CONCLUSIONS: The autonomic failure following SCI seems to be a time-dependent phenomenon, which tends to improve with time. The spectral estimators of HRV may be useful and simple tools to monitor the changes in autonomic failure among SCI people. Whether exercise, pharmacological and other therapeutic strategies may affect such evolution remains to be elucidated.
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