Objectives: To characterize the continuity and duration of sleep, and to measure nocturnal cardiac autonomic balance via heart rate variability (HRV) in a group of emergency medical technicians (EMTs) on and off duty.
Methods: Fourteen EMTs completed an online, daily sleep log that recorded total sleep duration, bedtime, rise time, and the number of alarms that caused awakening. HRV was captured using a physiological status monitor (PSM) affixed to a chest strap during sleep.
Results: For the 7-day trial, each of the 14 EMTs logged three work days (WDs) and four non-work days (NWDs). They reported sleeping significantly fewer hours per night on WDs (6.4 ± 2.1) than on NWDs (7.9 ± 0.5; P < 0.05), and experienced more sleep disruptions on WDs (4.4 ± 2.8) than on NWDs (1.3 ± 2.2; P < 0.001) as measured by the number of alarms. Global and vagal indices of HRV during sleep were significantly reduced during WDs (Standard Deviation of Normal R-R Intervals (SDNN) = 43.4 ± 2.0 ms and High Frequency (HF) = 24.3 ± 1.2 ms2) when compared to NWDs (SDNN = 61.1 ± 1.0 ms and HF = 42.7 ± 1.5 ms2; P < 0.001).
Conclusion: EMTs who worked 24-hour shifts had shorter, more fragmented sleep associated with greater cumulative exposure to increased sympathetic and decreased parasympathetic activity as measured via sleep HRV. These changes in cardiac autonomic tone constitute one plausible pathway through which sleep deprivation may increase risk for cardiovascular disease.
Keywords: EMT; heart rate variability; sleep.