Alternations in Circadian Variation in Heart Rate Variability in Patients after Cervical Spinal Injury.

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Introduction : Cervical spinal cord injury patients are known to suffer from the autonomic nervous system (ANS) failure as a result of their injury. Surgical stimulation may trigger sympathetic and parasympathetic afferents below the level of the lesion that are not inhibited by supraspinal centers. This can lead to deteriorate the ANS activity after the surgery. Analysis of the heart rate variability (HRV) can assess the changes in the ANS activity.This study was performed to evaluate the ANS activity after the spinal surgery under the general anesthesia.Method : After institutional approval and informed consent, 12 patients (ASAPS 1 or 2) were evaluated. Cervical fixation and decompression was carried out for six patients with cervical spondylosis and six patient with the posterior longitudinal ligament. Twenty-four hour EEG recordings were obtained for each patients with a active tracer (AC300, Suwa Trust, Tokyo). Measurements were performed on 2 day before surgery (PRE) and postope … More rative -1 (POD1), 3 (POD3), 7 (POD7) days. Power spectra were calculated with a maximum entropy method (Memcalc system, Suwa Trust, Tokyo). The power spectrum of HRV was divided into two different frequency bands : high-frequency component (HF:0.l5-0.40 Hz), low-frequency component (LF:0.04-0.15 Hz), and the ratio(HF/LF). The HF was used to reflect the vagally medicated activity and the LF to reflect both sympathetic and parasympathetic influences. The LF/HF ratio was calculated in order to mirror the sympathovagal balance. The variables were analyzed in 24-hours periods and also in daytime (8:00-21:00) and night-time (21:00-8:00) at baseline (PRE), POD1, POD3, and POD7. Difference from the baseline value were analyzed with repeated measure one-way ANOVA and significance was considered for values of p < 0.05. All data were expressed as mean ± SD.Result : LF and HF in night-time, daytime and 24-hours increased at POD1 as compared to PRE. They decreased at POD3 and POD7. The diminished circadian variation in HRV before surgery recovered within a week after the surgery.Conclusion : These data demonstrate that surgical procedure and general anesthesia altered the sympathetic and parasympathtic function in patients with cervical spinal cord injury. We found by comparing daytime and night-time HRV variables, that patients demonstrated alterations in a pattern of circadian rhythm city within a week after the surgery. The role of the changes in the ANS activity and circadian variations of HRV induced by the surgical procedure and anesthesia is still unclear and further studies will be needed in patients with cervical spinal cord injury. Less