Adverse Impact of Sleep Restriction and Circadian Misalignment on Autonomic Function in Healthy Young Adults

Abstract

Insufficient sleep and circadian rhythm disturbances have been each associated with adverse cardiovascular outcomes in epidemiologic studies, but experimental evidence for a causal link is scarce. The present study compares the impact of circadian misalignment (CM) to circadian alignment (CA) on human autonomic function using a nonrandomized parallel group design to achieve the same total sleep time in both conditions. Following baseline assessments (three days with 10h bedtimes), 26 healthy young adults were assigned to sleep restriction (SR; eight 5h bedtimes) with either fixed nocturnal bedtimes (CA; n=13) or bedtimes delayed by 8.5h on 4 of the 8 days (CM; n=13). Daytime ambulatory blood pressure (BP) and heart rate (HR, CA: n=11, CM: n=10), and 24-hour urinary norepinephrine levels (NE, CA: n=13, CM: n=13) were assessed at baseline and the end of SR. Nocturnal HR and heart rate variability (HRV) were analyzed during sleep at baseline and during the 4th and 7th nights of SR (CA: n=8, CM: n=12). SR resulted in a significant increase in daytime HR in both groups, without changes in BP. SR increased 24-hour urinary NE in the CM group (30±4 vs. 21±2 μg), but not in the circadian alignment group (group×condition, p=0.005). In contrast to the lack of detectable impact of CM on daytime autonomic function, SR with CM elicited greater increases in nocturnal HR, as well as greater reductions in vagal indices of HRV, than SR without CM (group×condition, p<0.05). In conclusion, SR and CM both result in impaired autonomic function that could lead, under chronic conditions, to enhanced cardiovascular risk.

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