[49] Wehrens SM, Hampton SM, Skene DJ. Heart rate variability and endothelial function after sleep deprivation and recovery sleep among male shift and non-shift workers. Scand J Work Environ Health. 2012 Mar;38(2):171–181. doi: 10.5271/sjweh.3197. Epub 2011 Sep 27. PMID: 21953310. RefID-556 PMID-21953310
Study Setting	Clinical investigation unit. University of Surrey, United Kingdom
Eligible Participants	Male shift and non-shift workers aged between 25–45 years.
Study Aims	The aim of this study was to investigate the effect of one night of total sleep deprivation, a recovery nap, and recovery sleep on FMD and HRV in controlled laboratory conditions and to assess the responses of experienced shift compared to non-shift workers in the same study.
Study Design & Participants	This experimental study design consisted of eleven experienced male shift workers who had a history of shift work ≥5 years and 14 non-shift workers that were matched for age, body mass index, and cholesterol levels. HRV parameters [e.g., HR variance and low frequency/high frequency]. They spent four days and nights in a clinical investigation unit. Following an adaption night of sleep of around 8 h, the subjects stayed awake for 30.5 h with a 4 h recovery nap.
Intervention	Participants had an adaptation night and baseline night. Subjects were required to stay awake for 30.5 h until their 4 h recovery nap. After this, they had a recovery sleep at habitual bedtime. Subjects were continuously monitored during wake time. All interventions and measurements were scheduled to each subject’s self-selected wake-up time. The subjects were asked to sleep in a semi-recumbent position. Assessments were completed in supine positioning.
Comparison(s)	A baseline FMD was measured from the shift worker group and the non-shift worker group. FMD was next measured after 30.5 h of awake time. FMD was last measured after a 4 h nap following sleep deprivation. FMD can be seen from both comparison groups in Figure 3 in Wehrens et al., 2012 [49].
Outcome Measure(s)	The primary outcome of this study was to compare HRV and endothelial function after sleep deprivation among shift workers. Polysomnography was used to assess wakefulness during the sleep deprivation period. High resolution ultrasound machines were used to access endothelial function of the brachial artery. FMD used 220 frames, ECG triggered images, ultrasound probe, and brachial artery location.
Key Finding(s)	As seen in Figure 3 in Wehrens et al., 2012, there is a trend of lower FMD among shift workers. It is difficult to determine quantitative results from Figure 3 (in Wehrens et al., 2012) displaying the comparison group FMD data. Contradictory statements made from the results section: “The %FMD among both shift and non-shift workers in the morning and afternoon is shown in Figure 3 in Wehrens et al., 2012. There were no significant effects of day, time, group, or interactions on %FMD.”