Sleep Variability and Cardiac Autonomic Modulation in Adolescents: The Penn State Child Cohort

Introduction: The association between habitual sleep patterns and cardiac autonomic modulation (CAM) in adolescents is not fully understood. We investigated such association in the population-based Penn State Child Cohort (PSCC) follow-up examination.

Methods: An actigraph (GT3X) and a sleep diary were used in 421 adolescents for 7 consecutive nights to calculate nightly sleep time and sleep efficiency. We calculated within-subject 7-night means and the standard deviations (SDs). The means being used as the individual’s habitual sleep duration and efficiency. The SDs were used as the individual’s habitual variability of sleep duration and efficiency. CAM was assessed by heart rate variability (HRV) analysis of beat-to-beat normal R-R intervals from a 39-hour high resolution Holter ECG. The HRV indices in frequency domain [high frequency power (HF), low frequency power (LF), and LF/HF ratio] and time domain [standard deviation of normal RR intervals (SDNN), and the square root of the mean squared difference of successive normal RR intervals (RMSSD), and heart rate (HR)] were calculated on a 30-minute basis (78 repeated measures). Mixed-effects models were used to assess the relationships between habitual sleep variables and HRV relationships.

Results: The mean (SD) age was 16.7 y (2.3), with 52% male and 78% white. The mean (SD) of habitual sleep duration and its variability were 7.00 h (0.83) and 1.16 h (0.58), respectively. The mean (SD) of habitual sleep efficiency and its variability were 82% (6.2) and 7.0% (4.3), respectively. Higher sleep-duration-variability, but not mean sleep duration, was associated with lower HRV (all p<0.05). Similarly, higher sleep-efficiency-variability, but not mean sleep efficiency, was significantly associated with lower HRV (all p<0.05).

Conclusion: In adolescents, higher habitual sleep-duration-variability and higher sleep-efficiency-variability are associated with lower HRV, indicative of impaired CAM towards sympathetic overflow and reduced parasympathetic modulation. Habitual night-to-night sleep variability is a novel risk factor associated with cardiovascular morbidity.

Support: NIH R01 HL63772, R01 HL97165, UL1 RR033184, C06 RR16499, UL TR000127.