A Pilot Study Using a Smartwatch to Search for Biomarkers of Heart Rate Variability in Active Ulcerative Colitis

Introduction: Autonomic imbalance has been reported to correlate with clinical remission in patients with ulcerative colitis (UC). This study evaluated heart rate variability (HRV), a potential digital biomarker, in patients with active UC using a smartwatch that is easy to handle. Methods: Patients with active UC were recruited for this prospective study. The patients’ HRV was measured via the Fitbit Inspire2^™ linked via Bluetooth to their smartphone. HRV during nighttime sleep was obtained from continuous data. Patients were required to input the Simple Clinical Colitis Activity Index (SCCAI) score once daily by the application on their smartphones for 3 months. Results: Nine patients with UC were included. In clinically active disease, SCCAI scores showed a weak inverse relationship with parasympathetic activity, differences of successive R-R pulse intervals (RMSSD) (r = −0.44, p < 0.0001), high frequency (HF) (r = −0.42, p < 0.0001), and total autonomic nervous activity, low frequency (LF) (r = −0.43, p < 0.0001). Receiver operating characteristic analysis indicated that the RMSSD, HF, and LF were significantly higher in patients with active UC. Meanwhile, LF showed the most correlation with severity for bowel urgency scores. Conclusion: Longitudinal nighttime HRV recorded using a smartwatch is associated with disease activity in patients with active UC. In particular, RMSSD and HF, which are indices of the parasympathetic nervous system, have been suggested as potential digital biomarkers for UC.