Core Body Temperature Changes Prior to Sleep are Associated with Nocturnal Heart Rate Variability

Core body temperature (CBT) reductions occur prior to and during the sleep period, with the extent of pre-sleep reductions corresponding to sleep onset and quality. Pre-sleep reductions in CBT coincide with increased cardiac parasympathetic activity measured via heart rate variability (HRV), and while this appears to persist into the sleep period, individual differences in pre-sleep CBT decline and nocturnal HRV remain unexplored. The purpose of the current study was to assess the relationship between individual differences in pre-sleep CBT reductions and nocturnal heart rate (HR) and HRV in a population of 15 objectively poor sleeping adults (10 males, 5 females; age, 33 ± 4 years; BMI 27 ± 1 kg/m) with the hypothesis that blunted CBT rate of decline would be associated with elevated HR and reduced nocturnal HRV. Following an adaptation night, all participants underwent an overnight, in-laboratory sleep study with simultaneous recording of polysomnographic sleep including electrocardiography (ECG) and CBT recording. Correlations between CBT rate of change prior to sleep and nocturnal HRV were assessed. Blunted rate of CBT decline was significantly associated with increased heart rate (HR) in stage 2 (N2; R=.754, P=.001), stage 3 (N3; R=.748, P=.001), and rapid eye movement (REM; R=.735, P=.002). Similarly, blunted rate of CBT decline prior to sleep was associated with reduced HRV across sleep stages. These findings indicate a relationship between individual differences in pre-sleep thermoregulatory processes and nocturnal cardiac autonomic function in poor sleeping adults