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.
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.
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).
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.