Background: The diagnosis of major depressive disorder (MDD) is heterogeneous. For example, depressed patients exhibit varied patterns of sleep; both insomnia and hypersomnia are symptoms of depression. Assessment of sleep patterns in MDD is often limited by clinicians’ reliance on subjective self-ratings of sleep quality. Objective measures, such as sleep regularity measured by accelerometer data, may provide a more accurate understanding. This study assessed the extent to which objective sleep quality measures could detect differences among individuals with MDD. We hypothesized that we would observe variability in sleep regularity and patterns among depressed individuals. We also hypothesized that there would be a strong correlation between subjective sleep ratings and objective measurements.
Methods: Between April and October 2016, patients with MDD (n=4) and healthy volunteers (n=2) completed a protocol that involved tracking depressive symptoms and wearing Empatica E4 wristbands that recorded accelerometer data. Patients wore sensors 23 hours daily and were clinically assessed for depression symptoms and stress levels biweekly for 8 weeks using the Hamilton Depression Rating Scale (HDRS). We developed an algorithm to calculate objective sleep based on accelerometer data. We calculated sleep regularity indices for both objective and subjective sleep. We utilized Pearson correlation to compare sleep regularity indices and t-statistics to compare the sleep regularity between depressed and healthy samples.
Results: On average, the objective (accelerometer-based) and subjective (self-reported) sleep/awake time periods matched 74.52% of the time for each user (std=6.55%). A trend toward positive correlation between objective and subjective sleep regularity indices did not reach statistical significance in this small sample (r=0.79, p=0.06). Another trend that suggested depressed users had a lower objective sleep regularity index was also not significant (p=0.14).
Conclusion: Our analyses revealed that individuals’ subjective sleep ratings and objective data from the E4 sensors were potentially correlated but did not reach significance in this sample. Further analyses also suggested an association between lower objective sleep regularity and depressive symptoms as measured by the HDRS. We are continuing to recruit new patients for this protocol and further data will be reported from the larger sample during the conference.