Heart rate variability in patients with spinal cord injuries

In spinal cord injury both the level and the extension of the lesions have been related to different response to tilting in Low Frequency (LF) and High Frequency (HF) oscillations of heart rate. To understand the role of sympatho–vagal interaction in such patients, we tried to evaluate, using the LF/HF ratio, the residual possibility in maintaining the cardiovascular homeostasis. 9 subjects with different outcome of traumatic (4) and inflammatory (5) spinal cord involvement, with lesion between C6 and T10, were investigated with power spectral analysis of the blood pressure and heart rate variability in resting condition and during a period of head – up tilt test. The difference between the two conditions was tested using the Wilcoxon signed rank test. In patients with complete ASIA A lesion, the relatively preserved LF activity in resting condition did not increase during tilting, with a parallel decrease of LF/HF ratio. In patients with incomplete lesion (ASIA B, C, D), the LF power of R–R interval showed an inverse relation with the level of the lesion. The LF/HF ratio was partially maintained due to the concomitant adapting HF activity permitting an efficient sympatho–vagal balance