Evaluation of the Association of Pain and Disability Levels with Heart Rate Variability in Chronic Low Back Pain Patients

Background and/or Objectives: Low back pain (LBP) is a leading cause of disability and economic burden. Emerging evidence links impaired heart rate variability (HRV), a marker of autonomic nervous system function, to chronic pain. We hypothesized specific HRV indices correlate with pain and disability levels in individuals with chronic LBP.

Design: Cross-sectional observational study.

Setting : Physical therapy research clinic.

Participants : A convenience sample of 189 adults (≥18 years) with chronic LBP (pain≥3 months) were recruited from a larger observational cohort of 1000 individuals with chronic LBP.

Interventions: N/A

Main Outcome Measures: LBP intensity and disability were assessed using the Numeric Pain Rating Scale (NPRS) and Oswestry Disability Index (ODI). ODI scores were grouped into four categories (minimal, moderate, severe, and crippling disability). HRV data was collected using a Polar Verity sensor, with all participants recorded at rest for at least 5 minutes, providing a standardized time window for analysis and subsequently processed using Kubios Research Software (v4.1.1). Calculated HRV parameters included root mean square of successive differences (RMSSD), standard deviation of NN intervals (SDNN) (normal RR intervals excluding abnormal beats), percentage of RR intervals (time between successive R-peaks) differing by ≥50ms (pNN50), low-frequency (LF) and high-frequency (HF) power, and LF/HF ratio.

Results: Ordinal regression modeling showed LBP intensity scores were associated with RMSSD (LR = 7.5, p = 0.01), PNNxx (LR = 16.7, p < 0.01), HF power (LR = 7.3, p = 0.01), LF power (LR = 4.0, p = 0.05), and LF/HF ratio (LR = 35.3, p < 0.01), consistent with reduced parasympathetic activity. ODI was associated with PNNxx (LR = 9.2, p < 0.01), LF power (LR = 3.9, p = 0.05), and LF/HF ratio (LR = 9.6, p < 0.01).

Conclusions: Specific HRV indices were significantly associated with low back pain and disability levels, affecting parasympathetic tone and autonomic balance, though causality cannot be inferred from this study.