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.
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.
Study Type
INTERVENTIONAL
Allocation
RANDOMIZED
Purpose
OTHER
Masking
NONE
Enrollment
28
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.
University of Pittsburgh
Pittsburgh, Pennsylvania, United States
Number of participants with blunted dipping of blood pressure via the sleep based method
Blood pressure is created by the heart muscle contractions and is measured using two numbers: The Systolic Blood Pressure (SBP) and the Diastolic Blood Pressure (DBP). Normal patterns in BP include elevations in SBP and DBP during the daylight and waking hours followed by a drop (dip) during nighttime hours and during sleep. A dip of 10% to 20% during nighttime or sleep is considered normal, whereas a dip \<10% is defined as blunted BP dipping. Blunted BP dipping will be quantified as: \[(mean BP during waking hours - mean BP during sleep) / mean BP during waking hours\] X 100 - the "sleep-based method."
Time frame: Blood pressure will be monitored with automated devices at 1-hour intervals over 72 total hours
Number of participants with blunted dipping of blood pressure via the wide fixed time method
Blood pressure is created by the heart muscle contractions and is measured using two numbers: The Systolic Blood Pressure (SBP) and the Diastolic Blood Pressure (DBP). Normal patterns in BP include elevations in SBP and DBP during the daylight and waking hours followed by a drop (dip) during nighttime hours and during sleep. A dip of 10% to 20% during nighttime or sleep is considered normal, whereas a dip \<10% is defined as blunted BP dipping. Blunted BP dipping during nighttime hours (2300 to 0659 hours) vs. daytime hours (0700 to 2259 hours) will be quantified as: \[(mean daytime BP - mean nighttime BP) / mean daytime hours BP\] X 100 - the "wide-fixed time method."
Time frame: Blood pressure will be monitored with automated devices at 1-hour intervals over 72 total hours
The number of participants with unhealthy Heart Rate Variability (HRV) measured via the standard deviation of the inter-beat intervals of normal sinus beats (SDNN)
A healthy heart oscillates and beat-to-beat fluctuations are variable. Greater variability in heart rate is associated with better health, the capacity to respond and cope, and better performance. The Heart Rate Variability (HRV) measure standard deviation of the inter-beat intervals of normal sinus beats (SDNN) is considered standard and is calculated in milliseconds (ms) over short-term (e.g., 60 seconds) and long-term intervals (24 hours). Values of SDNN \<50ms are considered unhealthy for medical risk stratification.
Time frame: HRV will be monitored with a holter monitor continuously over 72 total hours
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