Skin thermoregulation is associated with cardiac vagal tone during sleep onset
Authors: Gonzalez Joshua , Robinson LaTroy , Clemons Noal , Ordaz Omar , Lynch Erin , Thosar Saurabh , McHill Andrew , Emens Jonathan , Shea Steven , Bowles Nicole 
Published: May 2023

Introduction: Core body temperature declines prior to nocturnal sleep onset via reduced heat production and changes in skin vasomotor tone. These thermoregulatory processes are partly influenced by the autonomic nervous system (ANS), as vessels regulating peripheral blood flow are innervated by sympathetic projections. Vasodilation in distal regions increases heat loss and the likelihood of sleep initiation. Indeed, the distal-to-proximal skin temperature gradient (DPG) is the best predictor of sleep onset latency. The inability to vasodilate and dissipate heat may be a physiological cause of sleep disturbances linked to ANS activity. Thus, we aimed to investigate the relationship between proximal and distal skin temperature and autonomic cardiac activity during sleep onset. We hypothesized that greater distal warming and proximal cooling during sleep onset would be associated with higher HRV. Methods: Fourteen participants (8 Females, age 41±9 y mean±SD, and BMI 26±4 kg/m2) maintained a self-selected bedtime for 1-3 weeks leading up to a laboratory visit. Temperature sensors (iButtons) were placed on the dorsal side of the non-dominant hand (distal) and the ipsilateral subclavicular region (proximal).Following an adaptation night, we analyzed polysomnography and electrocardiogram data beginning at habitual bedtime. Skin temperature was averaged for 15 minutes during supine rest in dim light (<3 lux) immediately preceding bedtime (lights out: LO, 0 lux) and compared to 15 to 45 minutes after sleep onset (30 min total). HRV was analyzed 5 min after LO before initiation of N2 sleep and standard indices of cardiac vagal tone were assessed (R-R interval, PNN50, and SDNN). A Pearson correlation across all participants was used to assess the relationship between changes in skin temperature and HRV following LO. Results: We observed negative correlations between the magnitude of proximal temperature increases across sleep onset and R-R interval (r=-0.56, p=0.03) as well as PNN50 (r=-0.67, p<0.01). Additionally, we observed a positive correlation between the magnitude of distal temperature increase and SDNN (r=0.53, p=0.04). Lastly, we observed a positive correlation between the change in DPG and SDNN (r=0.58, p=0.03). Conclusions: Our findings suggest that the magnitude of proximal and distal skin temperature fluctuations during sleep onset are associated with HRV. Specifically, those with higher vagal tone may also have greater shifts in heat redistribution during sleep onset. However, these findings are associative and we cannot determine mechanisms underlying the present relationship. Research Supplement to R01 HL142064 (SAS); R35 HL155681-01 to SAS; KL2TR002370andK01HL146992 to NPB; T32HL083808 to JEG; ORS 656.630 to Oregon Institute of Occupational Health Sciences at OHSU This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.