Impact of Intra-Shift Napping on EMS Cardiovascular Health
Condition: Blood Pressure; Heart Rate Variability
Study type: Interventional

Summary: 
      Cardiovascular disease (CVD) exerts a significant health burden among shift workers,
      including police, firefighters, and emergency medical services (EMS). The unique occupational
      demands inherent to these professions--sleep loss, circadian misalignment, high stress, and
      sustained hyper-vigilance--confer increased risk for both on and off-duty cardiovascular
      events. Mitigating cardiovascular risks in these professions requires that we first identify
      robust markers and potential mechanisms of risk. Previous work suggest shift work has a
      negative impact on blood pressure (BP) and heart rate variability (HRV). Blunted BP dipping
      at night and during sleep, and reduced HRV are powerful markers of increased CVD risk. Both
      are linked to preclinical indicators of cardiac damage, such as presence of coronary artery
      calcium, left atrial enlargement, and cardiovascular-related mortality. This study will use
      an experimental crossover study design with three intervention conditions to test the impact
      of a 30 minute brief nap and a 2-hour longer nap versus no nap on BP and HRV. Outcomes of
      interest include blunted dipping of BP during nighttime hours and during sleep and HRV.
    

Detailed description: 
      Cardiovascular disease (CVD) exerts a significant health burden among shift workers,
      including police, firefighters, and emergency medical services (EMS). The unique occupational
      demands inherent to these professions--sleep loss, circadian misalignment, high stress, and
      sustained hyper-vigilance--confer increased risk for both on and off-duty cardiovascular
      events. Mitigating cardiovascular risks in these professions requires that we first identify
      robust markers and potential mechanisms of risk. Previous work suggest shift work has a
      negative impact on blood pressure (BP) and heart rate variability (HRV). Blunted BP dipping
      at night and during sleep, and reduced HRV are powerful markers of increased CVD risk. Both
      are linked to preclinical indicators of cardiac damage, such as presence of coronary artery
      calcium, left atrial enlargement, and cardiovascular-related mortality.

      Critical questions remain:

      Are BP dipping and HRV impacted by napping during night shift work? Compared to those who do
      not nap, does napping during night shifts help BP and HRV to normalize quicker in the hours
      immediately post night shift work? What is the impact of brief naps (e.g., 30 minutes) versus
      longer naps (e.g., 2 hours)?

      This study will use a randomized crossover experimental design of EMS workers and be based in
      the laboratory environment. Participants will complete three intervention conditions. All
      study arms will involve a 12-hour simulated night shift. The intervention of interest is
      napping (no nap vs. a 30 minute nap vs. a two-hour nap) in a randomized crossover study
      design. The primary outcome of interest is BP dipping (>10% drop) and Heart Rate Variability
      (HRV) measured as the standard deviation of inter-beat intervals of the sinus beats in
      milliseconds (SDNN). All outcomes will be measured serially before the simulation, during
      simulated night shifts, during the intra-shift napping period, and during recovery.
    

Intervention name(s): Intra-Shift Napping
Intervention type(s): Behavioral
Intervention description(s): The Brief Nap opportunity will allow for a 30-minute nap between the hours of 0200 and 0400 during the 12-hour simulated night shift. The Longer Nap opportunity will allow for a 2-hour nap between the hours of 0200 and 0400 during the 12-hour simulated night shift.
Allocation: Randomized
Intervention model: Crossover Assignment
Intervention model description: Randomized crossover study design
Masking: None (Open Label)
Primary purpose: Other