Simultaneous monitoring of activity and heart rate variability in depressed patients: A pilot study using a wearable monitor for 3 consecutive days

INTRODUCTION: Reduced activity and sleep–wake rhythm disturbances are essential features of depressive episodes. In addition, alterations in heart rate variability (HRV) have been implicated in depression. By using a wearable sensor that monitors 3‐dimensional acceleration and HRV simultaneously, we examined the activity and HRV indices in depressive episode of mood disorders. METHODS: Participants were 19 patients (13 major depressive disorder [MDD] and 6 bipolar depression; 11 females) and 18 controls (9 females) matched for age and ethnicity (all Japanese) who completed 3 consecutive days of all‐day monitoring by a small and light device attached to the chest. RESULTS: Activity magnitude was significantly reduced while lying/resting time was increased in depressed patients, compared with controls. When males and females were examined separately, male, but not female, patients showed significant reduction in activity. HRV indices such as R‐R interval and high‐frequency power (a parameter for the parasympathetic system) were significantly decreased in patients than in controls. Significant differences in activity and HRV indices were seen only in males. Sympathetic load during sleep significantly correlated with damped rest–activity rhythm in depressed patients. LIMITATIONS: The number of participants was small, and the majority of the participants were taking psychotropic medications. CONCLUSIONS: We obtained evidence for reduced activity, increased lying/resting time, and reduced HRV indices in male depressed patients. The simultaneous monitoring for activity and HRV suggested greater sympathetic load during sleep is associated with damped rest–activity rhythm (increased activity during sleep and decreased daytime activity), which might be a characteristic pathology of depression.