Objective: Patients with complex regional pain syndrome type 1 might have disturbed autonomic function and increased heart rate fractal dynamics with a resultant impaired baroreflex sensitivity (BRS). We hypothesized that these parameters of impaired cardiovascular regulation might improve with a reduction of pain intensity.
Methods: Ten patients and 10 healthy volunteers entered the study. Power spectral analysis of heart rate (HR) variability was performed by the maximum entropy method. Ratios of low-frequency domain to high-frequency domain (LF/HF) and a fractal slope, the slope of a regression line of power spectral density (1/fβ), were calculated. BRS was assessed with a head-up tilt test. When the visual analogue scale scores decreased to ≦20 mm during treatments, those measurements were repeated.
Results: LF/HF and steepness of fractal slope before treatments decreased significantly during treatments when visual analogue scale was ≦20 mm (2.23±0.68 to 1.30±0.45, P=0.005 and −1.90±0.35 to −1.16±0.14, P=0.00032, respectively). BRS before treatments was low (−0.28±0.27 bpm/mm Hg) as compared with BRS of volunteers but significantly improved to −0.62±0.48 bpm/mm Hg during treatments (P=0.032).
Conclusions: Increased LF/HF ratios likely indicate that patients had an imbalance of the autonomic nervous system. The increased fractal slope suggests that patients developed strong self-similarity of HR variability. The highly predictable HR variability leads to impaired hemodynamic homeostasis, resulting in decreased BRS. The impaired cardiovascular regulation improved with a reduction of pain. Thus, spectral analysis of HR variability may be useful objectively to follow complex regional pain syndrome type 1 patients, not only for pain management but also for the status of cardiovascular stability.