From Subjective to Objective: The Bedside Value of HRV in AssessingChronic Pain Complicated by Emotionaland Sleep...

To test whether brief bedside photoplethysmography-derived heart-rate variability (PPG-HRV) provides objective information about pain, sleep, and affect in adults with chronic pain, and whether sleep moderates the pain-emotion association. We conducted a cross-sectional study of consecutive inpatients with chronic pain (duration ≥ 3 months) admitted to an orthopedics/traumatology service from March 31 to September 28, 2025. Adults (≥ 18 years; right-handed) were excluded for severe internal disease or acute trauma, major psychiatric disorders, marked cognitive impairment, or recent use of anxiolytics/hypnotics. At admission, 5-min fingertip PPG-HRV was recorded under standardized bedside conditions, with artifact correction, stationarity checking, and quality-control screening applied before analysis. Outcomes were the Brief Pain Inventory-Short Form (BPI-SF), Hamilton Depression Rating Scale (HAMD-24), Hamilton Anxiety Rating Scale (HAMA-14), and a composite "sleep problems" index computed as the mean of z-scored HAMD insomnia items and the BPI-SF sleep-interference item. Analyses included correlations, cross-validated random-forest regression incorporating logarithmically transformed HF power (lnHF), and Hayes' PROCESS Model 1 testing sleep as a moderator of the pain→emotion pathway. A total of 172 patients were enrolled (37.2% men; mean age 59.2 years). lnHF was significantly associated with HFnorm, pain, sleep disturbance, and depression, but not anxiety. Random-forest models showed the strongest predictive performance for sleep disturbance (R²_CV = 0.844), followed by depression (R²_CV = 0.696) and pain-related burden (R²_CV = 0.506), whereas anxiety showed limited predictive performance (R²_CV = 0.009). HFnorm and lnHF emerged as recurrently important predictors of pain, sleep disturbance, and depressive symptoms. In moderation analyses, pain×sleep interactions were significant for anxiety (model R² = 0.465; β = 0.159; ΔR² = 0.026; p < 0.01) and depression (model R² = 0.513; β = 0.252; ΔR² = 0.066; p < 0.001). Brief bedside PPG-HRV, particularly HF-related indices such as lnHF and HFnorm, provides auxiliary physiological information related to pain, sleep disturbance, and depressive symptoms in hospitalized adults with chronic pain. Sleep disturbance amplified the association between pain and emotional symptoms, supporting the clinical relevance of the pain-sleep-emotion pathway. HRV is not suitable for diagnosis or stand-alone decision-making, but may serve as a practical adjunctive marker for risk stratification and symptom monitoring.