Predicting & Tracking COVID-19 Infections: Sleep Number Smart Bed Sleepers Shows a Potential Model adminJuly 28, 2023 HRV, the variation in time between heartbeats, is commonly used to assess the activity of the autonomic nervous system (ANS), which unconsciously regulates certain essential bodily functions including breathing, heart rate, blood pressure, and others. Changes to autonomic nervous system function, reflected in HRV, can result from factors including lifestyle, aging, cardiorespiratory illnesses, sleep state, and physiological stress. HRV is lower under situations of stress, either emotional or physical, and is higher in relaxed states. While there is broad interest in researching HRV, few studies to date have established normative overnight HRV values for a large population. An analysis of overnight standard deviations in normal-to-normal (SDNN) heartbeat intervals from 18.2 million sleep sessions from 379,225 Sleep Number 360 smart bed sleepers was conducted to better understand population-level HRV changes. Higher SDNN numbers generally correlate with better health and cardiac response to stress, and lower SDNN numbers are an indicator of unhealthy cardiac activity. Results of the analysis found significant cross-sectional associations between overnight SDNN and age, gender and day of the week. For sleepers under 50 years old, SDNN declined at a rate of about 2.1 milliseconds/year, then leveled off for sleepers aged 50-65, and increased slightly thereafter. Women under 50 showed lower, more slowly declining SDNN values than men, but this trend reversed for sleepers over 50. Additionally, SDNN values were generally highest over the weekend and lowest at mid-week. SDNN values for women followed a U-shaped pattern, starting high in the beginning of the week, dipping mid-week, then increasing through the weekend, whereas values for men followed an L-shaped pattern, starting high in the beginning of the week, but quickly fell and stayed low through the week. These results show measuring overnight SDNN data using the 360 smart bed may be a useful, ecologically valid device for evaluating population health models reliant on heart rate variability.