Napping on the night shift and its impact on blood pressure and heart rate variability among emergency medical services workers: study protocol for a randomized crossover trial

Abstract

Background There is an emerging body of evidence that links exposure to shift work to cardiovascular disease (CVD). The risk of coronary events, such as myocardial infarction, is greater among night shift workers compared to day workers. There is reason to believe that repeated exposure to shift work, especially night shift work, creates alterations in normal circadian patterns of blood pressure (BP) and heart rate variability (HRV) and that these alterations contribute to increased risk of CVD. Recent data suggest that allowing shift workers to nap during night shifts may help to normalize BP and HRV patterns and, over time, reduce the risk of CVD. The risk of CVD related to shift work is elevated for emergency medical services (EMS) shift workers due in part to long-duration shifts, frequent use of night shifts, and a high prevalence of multiple jobs. Methods We will use a randomized crossover trial study design with three study conditions. The targeted population is comprised of EMS clinician shift workers, and our goal enrollment is 35 total participants with an estimated 10 of the 35 enrolled not completing the study protocol or classified as lost to attrition. All three conditions will involve continuous monitoring over 72 h and will begin with a 36-h at-home period, followed by 24 total hours in the lab (including a 12-h simulated night shift), ending with 12 h at home. The key difference between the three conditions is the intra-shift nap. Condition 1 will involve a simulated 12-h night shift with total sleep deprivation. Condition 2 will involve a simulated 12-h night shift and a 30-min nap opportunity. Condition 3 will involve a simulated 12-h night shift with a 2-h nap opportunity. Our primary outcomes of interest include blunted BP dipping and reduced HRV as measured by the standard deviation of the inter-beat intervals of normal sinus beats. Non-dipping status will be defined as sleep hours BP dip of less than 10%. Discussion Our study will address two indicators of cardiovascular health and determine if shorter or longer duration naps during night shifts have a clinically meaningful impact. Trial registration ClinicalTrials.gov NCT04469803. Registered on 9 July 2020

The effect of extended shift work on autonomic function in occupational settings: A systematic review and meta-analysis

“…Thirty‐six studies 16,22,56–89 were excluded because they did not investigate a 24‐h shift and 15 studies 90–104 did not have a continuous shift or had an unclear or undefined shift length. One study 105 was excluded because it did not compare the effect of shift work after 24 h. In addition, one study 106 was excluded because it was not available in the English language, three studies 107–109 used sleep as an experimental condition, and one study 110 was a letter to the editor. The excluded studies, with reasons for exclusion at full‐text screening, are described in Table S3.…”

The effect of a night shift nap on post-night shift performance, sleepiness, mood, and first recovery sleep: A randomized crossover trial

“…We conducted a randomized crossover trial with participants assigned to three separate 72-hour conditions comprised of 36 hours of at-home monitoring (07:00–19:00 + 1 day), followed by a 12-hour in-lab night shift (19:00–07:00), 12-hour in-lab recovery opportunity (07:00–19:00), and 12-hour at-home recovery opportunity (19:00–07:00) ( 12 ). Two intervention conditions included a nap that began at 02:00 (30 minutes or 2 hours) during the simulated night shift.…”

“…Nap-specific measures were assessed immediately pre-nap and again at +0, +10, +20, and +30 minutes post-nap. Participants wore multiple non-invasive physiological devices throughout each condition (findings reported elsewhere) ( 12 , 20 ) and completed the Brief 3-minute version of the Psychomotor Vigilance Test (PVT-B) ( 21 ). The PVT-B measured reaction time [RT in milliseconds (ms)], lapses (RT>355ms), false starts (reactions before stimulus or RT<100ms), and speed (1000/RT) ( 21 ).…”

“…In this secondary analysis of a randomized crossover trial ( 12 ), we test the effect of a 30-minute versus 2-hour nap opportunity taken during a simulated night shift on cognitive performance, fatigue, sleepiness, mood states, and sleep at the end of shift and throughout the immediate post-night shift recovery opportunity. We focus on the post-night shift recovery opportunity given that many night shift workers, especially in public safety and certain healthcare settings, may have the opportunity for longer naps during night shift work (ie, 2 hours) ( 13 ) and may subsequently experience delays in obtaining sleep post-night shift due to the required commute home and non-work related responsibilities that can only be completed during daylight hours (eg, childcare, running errands).…”

The critical role of epigenetic mechanism in PM2.5-induced cardiovascular diseases

“…Hyang-Min et al found that mtDNA methylation in the blood of people exposed to PM 2.5 is negatively correlated with PM 2.5 concentration, and also found that the heart rate variability of subjects with higher mtDNA methylation levels is more likely to be affected by PM 2.5 [ 42 ]. As we all know, heart rate variability is a very valuable indicator for predicting sudden cardiac death and arrhythmia events, and can be used to determine the condition and prevention of CVD [ 43 ]. In recent years, some studies have begun to pay attention to the relationship between PM and heart rate variability to speculate on important risk factors for CVD [ 44 , 45 ].…”