LAUSR

Sleep, circadian rhythms, and thermoregulatory physiology are highly integrated and impact each other. The daily rhythm in the distal-proximal skin temperature gradient (DPG) is wider/more negative during wakefulness, and narrower/closer to zero during sleep. The circadian rhythm in the DPG is wider during the biological day and narrower during the biological night. Here we aimed to quantify and compare the amplitude of the daily rhythm in the DPG under wakefulness-sleep conditions versus the amplitude of the circadian rhythm in the DPG under sleep deprivation conditions to examine associations and magnitude differences. Eleven [5 females] healthy adults [aged 27.6±10.2y, BMI 23.1±2.2 (mean±SD)] participated. After one week of at-home ambulatory monitoring with 8h per night sleep opportunities at habitual bedtimes, participants were studied in the laboratory for three days under controlled dim light (< 8 lux maximum) and ambient temperature conditions (22-24°C). Participants arrived in the afternoon, were kept awake 4h later than typical and scheduled to a 4h sleep opportunity. The next day, participants were sleep deprived for 28h followed by recovery sleep. Skin temperature was assessed every min with iButtons placed subclavicular (proximal skin temperature) and foot palmar (distal skin temperature). The DPG was calculated as difference between proximal and distal skin temperatures. A three-harmonic regression model was used to fit DPG data and derive daily and circadian rhythm amplitudes, and percent difference in amplitude was calculated. Pearson correlations were calculated between daily and circadian rhythm DPG amplitudes. DPG amplitude was significantly greater for daily versus circadian rhythm (p < 0.05). Percent difference analyses showed daily DPG rhythm was 57% larger than circadian DPG rhythm (SD 30%, range 22-134%). A significant correlation was found between daily and circadian rhythm DPG amplitudes (r = 0.71, p< 0.05). The amplitudes of daily and circadian rhythms of the DPG are associated, but the daily rhythm amplitude is larger. Additional research is needed to compare the relative importance of daily versus circadian skin temperature amplitudes for sleep and circadian relevant outcomes. CurAegis Technologies Inc., Fundacio Joan Riera I Gubau, Undergraduate Research Opportunities Program University of Colorado Boulder