Perceived disability but not pain is connected with autonomic nervous function among patients with chronic low back pain.

OBJECTIVE To assess the association of cardiovascular autonomic balance with perceived functional impairment and pain among patients with chronic low back pain. DESIGN A cross-sectional analysis of working patients with chronic low back pain. PATIENTS Forty-six consecutive patients aged 24-45 years with chronic low back pain fulfilling the inclusion criteria. A total of 39 subjects had technically acceptable electrocardiographic recordings during periods of rest and standard provocations. METHODS Perceived functional disability was assessed with the Oswestry disability index and pain with a numerical rating scale. Autonomic nervous function was assessed by measuring heart rate variability with short recordings. RESULTS The total power of heart rate variability was lower among those with moderate perceived disability (Oswestry 20-40%) compared with those with minimal disability (Oswestry < 20%). However, heart rate variability did not differ significantly among those with numerical rating scale values < or = 5/10 from those with values > 5/10. The power of the high-frequency component (0.15-0.4 Hz) of heart rate variability was lower among those with moderate perceived functional impairment. CONCLUSION A significant association existed between heart rate variability and perceived physical impairment, but not between heart rate variability and pain. Proportionally reduced high-frequency activity was found to reflect decreased parasympathetic activity or increased sympathetic activity. This resulted in sympathetic dominance among the patients with higher subjective disability. The possible clinical implications of this observation are discussed.