The Impact of Autonomic Nervous System Modulation on Heart Rate Variability and Musculoskeletal Manifestations in Chronic Neck Pain: A Double-Blind Randomized Clinical Trial

<b>Background:</b> The role of autonomic nervous system (ANS) modulation in chronic neck pain remains elusive. Transcutaneous vagus nerve stimulation (t-VNS) provides a novel, non-invasive means of potentially mitigating chronic neck pain. This study aimed to assess the effects of ANS modulation on heart rate variability (HRV), pain perception, and neck disability. <b>Methods:</b> In this double-blind randomized clinical trial, 102 participants with chronic neck pain were randomly allocated to one of three groups: t-VNS plus standard-care physiotherapy (SC-PT), heart rate variability biofeedback (HRV-BF) with SC-PT, or SC-PT alone. Interventions were administered three times weekly for 6 weeks. The following outcome measures were assessed at baseline and after 6 weeks: HRV, the visual analog scale (VAS), the pressure pain threshold (PPT), and the neck disability index (NDI). <b>Results:</b> The t-VNS group exhibited significant improvements compared to the HRV-BF and SC-PT groups. Specifically, t-VNS increased the RR interval (mean difference [MD] = 35.0 ms; <i>p</i> = 0.037) and decreased the average heart rate (MD = -5.4 bpm; <i>p</i> = 0.039). Additionally, t-VNS reduced the VAS scores (versus HRV-BF: MD = -0.8 cm, <i>p</i> = 0.044; SC-PT: MD = -0.9 cm, <i>p</i> = 0.018), increased the PPT (versus HRV-BF: MD = 94.4 kPa, <i>p</i> < 0.001; SC-PT (MD = 56.2 kPa, <i>p</i> = 0.001)), and lowered the NDI scores (versus HRV-BF: MD = -4.0, <i>p</i> = 0.015; SC-PT: MD = -5.9, <i>p</i> < 0.001). <b>Conclusions:</b> t-VNS demonstrated superior effectiveness compared to HRV-BF and SC-PT in regulating HRV, alleviating pain, and enhancing functional capabilities in individuals with chronic neck pain.