Wearables as Translational Physiomarkers and Clinical Endpoints in Insomnia Research: Can Sleep Research Advance Psychiatry?

Wearables that integrate actigraphy and pulse photoplethysmography (ACT + PPG) could represent a promising advancement in insomnia research and clinical practice. This especially applies to assessing objective sleep for a longer period in the home environment, which is impractical with ambulatory polysomnography (PSG) whereas actigraphy alone struggles with detecting wake-after-sleep-onset, as one of the most important variables for insomnia research (on which further variables, such as sleep efficiency, depend). The addition of heart rate and heart rate variability data to actigraphy strongly enhances WASO detection, offering hope for objective WASO detection for insomnia. For further physiomarker development, several challenges of ACT + PPG need to be tackled. Current commercial solutions often rely on "black-box" algorithms trained on small, healthy samples, leading to inaccuracies in sleep-disordered populations. Moreover, the lack of access to raw data hinders validation and cross-study comparability. These and other issues are addressed in detail in this opinion paper in order to raise awareness and start a discussion about more reliable, objective sleep markers that could be readily used as objective clinical endpoints in clinical trials on cognitive-behavioural therapy for insomnia (CBT-I) or stress-related mental disorders and novel pharmacological compounds. The sleep research community has the opportunity to establish ACT + PPG as a gold standard of home based, longitudinal sleep monitoring, which has the potential to bridge the gap between research and clinical practice, transforming clinical trials and improving psychiatric care.