Assessment of Sleep by WHOOP in Ambulatory Subjects

Polysomnography (PSG) is still considered the 'gold standard' for measuring sleep parameters, such as total sleep time, sleep efficiency, and sleep stages (6). However, PSG suffers from key limiting factors for routine care applications irrespective of setting (e.g., home, acute setting, and long term setting). Some of the key limitations of PSG are the high cost, arduous application, intrusiveness to sleep, and requirement of sleep lab and dedicated infrastructure. Wearable technologies could provide a viable alternative to PSG. We are proposing to perform a methodological study aimed at validating the accuracy of WHOOP Strap 2.0 to measure sleep quantity and sleep quality in ambulatory subjects. We will measure sleep by both WHOOP Strap 2.0 and PSG in healthy volunteers (age 18 - 45 years) without self-reported sleep disorders or chronic disabling medical conditions. In ambulatory patients, sleep is usually assessed by the American Academy of Sleep Medicine guidelines which derives from the Rechtschaffen and Kales (R\&K) method with good to excellent inter-observer reliability for assessing sleep in the same population; but the Cohen's K range is still 0.68 to 0.82 and much lower for non rapid eye movement (NREM) sleep stage 1 (N1). To account for such inter- and intra-rater reliability issues with the PSG gold-standard, we will only consider sleep stages that are unequivocally scored as a particular stage (light NREM, slow wave sleep \[SWS\] or REM sleep \[R sleep\]) by two different observers. Additionally, while there are many devices available to healthy individuals to measure heart rate, there aren't many available that provide a daily heart rate variability statistic. Heart rate variability can be defined as the variation over time of the period between consecutive heart beats. This is due to the balancing regulation effects of the parasympathetic (PNS) and sympathetic (SNS) actions of the autonomic nervous system (ANS). Increased SNS action results in a "fight or flight" response, leading to an accelerated heart rate, while increased PNS activity results in a "rest and digest" response, leading to a decelerated heart rate. The increased variability of heart rate (HR) is an indication of the ANS' control on HR and the heart's ability to respond. WHOOP Strap 2.0 provides users with real-time HR and a daily HRV statistic that is included in other variables calculated measuring daily strain and recovery statistics. We will measure HR and HRV by both WHOOP Strap 2.0 and EKG leads in healthy volunteers (ages 18-45 years) without chronic disabling medical conditions.