Objective Assessment of Pediatric Musculoskeletal Pain Using Heart Rate Variability, Pupil Diameter, Blood Pressure, and Respiratory Rate

Introduction Pain assessment in children is challenging as Visual Analog Scale (VAS) may be influenced by age, communication ability, and emotional state. Physiological parameters in chronic musculoskeletal pain were measured to corelate and objectify the pain intensity with VAS. Methods In this prospective observational study, 104 children with musculoskeletal disorders were enrolled and pain intensity was assessed using the Visual Analog Scale (VAS). Physiological parameters including heart rate variability [HRV: Standard Deviation of NN intervals (SDNN), Root Mean Square of Successive Differences (RMSSD), Number of pairs of successive NN intervals that differ by more than 50 ms (NN50), and Proportion of NN50 (pNN50)], respiratory rate, systolic and diastolic blood pressure (SBP, DBP) centiles and pupil diameter were also measured. Results The mean age children were 8.88 ± 1.69 years with a mean VAS score of 4.75 ± 2.36. Pain intensity of VAS showed a negative correlation with SDNN (ρ = −0.884), RMSSD (ρ = −0.870), NN50 (ρ = −0.774), and pNN50 (ρ = −0.767) (all p < 0.001). Significant positive correlations were observed between VAS scores and respiratory rate (ρ = 0.784), SBP centile (ρ = 0.762), DBP centile (ρ = 0.782), and pupil diameter (ρ = 0.820) (all p < 0.001). Children with idiopathic musculoskeletal pain exhibited higher HRV than those with inflammatory arthritis. ROC analysis identified clinically useful cut-off values for moderate (VAS ≥ 4) and severe pain (VAS ≥ 7). Conclusions Strongest association of HRV and other physiological parameters with pain severity may serve as valuable adjuncts for pain assessment.