Remote Prediction of Cardiorespiratory Fitness in a Preoperative Cohort: Exploring Short and Long-term Heart Rate Variability

Background Wearable sensors offer a scalable alternative to cardiopulmonary exercise testing for assessing cardiorespiratory fitness, and there is growing evidence to support their use for remote VO ₂ max estimation. This study investigated whether heart rate variability (HRV) measures derived from wearable ECG sensors improve VO ₂ max estimations in a preoperative cohort and compared the relative contributions of short- and long-term HRV features. ECG and accelerometer data from 198 participants scheduled for major abdominal surgery (REMOTES study, ClinicalTrials.gov: ID NCT06042023) were collected over 72 hours. Measures including physical activity, steps, heart rate, and HRV were extracted. Short-term (5-minutes) and long-term (24-hour) heart rate variability features were extracted from free-living ECG data. Two LASSO regression models with five-fold cross-validation were developed: a baseline model (excluding HRV) and a HRV model. Results After exclusions, 163 participants were included in analyses. The HRV model outperformed the baseline across all metrics, achieving a higher R ² (0.47 ± 0.12 vs 0.42 ± 0.13) and lower mean absolute error (2.63 ± 0.34 vs. 2.77 ± 0.38 ml/kg/min), root mean square error (3.38 ± 0.53 vs 3.54 ± 0.57 ml/kg/min) and absolute percentage error (15.55 ± 2.19% vs. 16.22 ± 2.45%). Analysis of feature contributions identified long-term HRV (SDANN _HR 24), age, gender, and step-counts as key contributors to model performance. Conclusion HRV features from wearable data, especially long-term measures, can improve remote VO ₂ max predictions in a clinical cohort. While performance gains were modest, these findings support the integration of HRV features into remote monitoring systems in real-world settings. Long-term HRV measures derived from heart rate signals offer a practical option for cardiorespiratory fitness assessment, requiring minimal additional processing. Trail Registration: This study was registered at ClinicalTrials.gov (Clinical trial number: NCT06042023) and was registered retrospectively on 11/09/2023.