Objective: Blunting of the sleep-related dip in blood pressure (BP) has been linked to numerous cardiovascular outcomes including myocardial infarction. Blunting of BP dipping occurs during night shift work and previous research suggest that a 60-min or longer on-shift nap is needed to restore normal/healthy BP dipping. We sought to determine the effect of different durations of napping on BP during and following simulated night shifts. We hypothesized that the greatest benefit in terms of restoration of normal BP dipping during night shift work would be observed during a longer duration nap versus a shorter nap opportunity.
Methods: We used a randomized crossover laboratory-based study design. Participants consented to complete three separate 72-hr conditions that included a 12-hr simulated night shift. Nap conditions included a 30-min and 2-hr nap compared to a no-nap condition. Ambulatory BP monitoring was assessed hourly and every 10-30 mins during in-lab naps. Blunted BP dipping during in-lab naps was the primary outcome. Goal enrollment of 25 (35 with attrition) provided 80% power to detect a mean difference of 5 mmHg in BP between nap conditions.
Results: Of the 58 screened, 28 were consented, and 26 completed all three 72-hr conditions. More than half (53.6%) were female. Mean age was 24.4 years (SD7.2). Most (85.7%) were certified as emergency medical technicians or paramedics. The mean percentage dip in systolic BP (SBP) and diastolic BP (DBP) did not differ between the 30-min and 2-hr nap conditions (p > 0.05), yet a greater proportion of participants experienced a 10-20% dip in SBP or DBP during the 2-hr nap versus the 30-min nap (p < 0.05). For every additional minute of total sleep during the 30-min nap, the percentage of SBP dip improved by 0.60%, and the percentage of DBP dip improved by 0.68% (p < 0.05). These improvements approximate to a 6% per minute relative advancement toward normal/healthy BP dipping.
Conclusions: Restoration of a normal/healthy dip in BP is achievable during short and long duration nap opportunities during simulated night shift work. Our findings support the hypothesis that BP dipping is more common during longer 2-hr versus shorter 30-min naps.
Trial registration: ClinicalTrials.gov, NCT04469803. Registered on 9 July 2020.