Abstract
Shiftwork has been associated with elevated blood pressure (BP) and decreased heart-rate variability (HRV), factors that may increase the long-term risk of cardiovascular-related mortality and morbidity. This study explored the effect of shiftwork on dynamic changes in autonomic control of HRV (cardiac stress), systolic BP and diastolic BP, i.e., SBP and DBP (vascular stress), and recovery in the same subjects working different shifts. By studying the same subjects, the authors could reduce the effect of possible contribution of between-subject variation from genetic predisposition and environmental factors. The authors recruited 16 young female nurses working rotating shifts—day (08:00–16:00 h), evening (16:00–00:00 h), and night (00:00–08:00 h)—and 6 others working the regular day shift. Each nurse received simultaneous and repeated 48-h ambulatory electrocardiography and BP monitoring during their work day and the following off-duty day. Using a linear mixed-effect model to adjust for day shift, the results of the repeated-measurements and self-comparisons found significant shift differences in vascular stress. While working the night shift, the nurses showed significant increases in vascular stress, with increased SBP of 9.7 mm Hg. The changes of SBP and DBP seemed to peak during waking time at the same time on the day off as they did on the working day. Whereas HRV profiles usually returned to baseline level after each shift, the SBP and DBP of night-shift workers did not completely return to baseline levels the following off-duty day (p < .001). The authors concluded that although the nurses may recover from cardiac stress the first day off following a night shift, they do not completely recover from increases in vascular stress on that day. (Author correspondence: jdwang@ntu.edu.tw)
Highlights
Shiftwork has been associated with elevated blood pressure (BP) and decreased heart-rate variability (HRV), two factors that may increase the long-term risk of cardiovascular disease mortality and morbidity (Furlan et al, 2000; Harrington, 1994; Knutsson et al, 1986; Taylor & Pocock, 1972; Tenkanen et al, 1997; Vrijkotte et al, 2000)
The dynamic changes of simultaneous HRV and BP recordings for work days and consecutive off-duty days categorized by shift are summarized in Figure 1, which in the top panel presents the values for the outpatient clinic (OPC)
Using a linear mixed-effect model, we found work-time systolic blood pressure (SBP) of the nurses when working the night shift to be significantly higher (9.7 mm Hg) than when working the day shift ( p < .001)
Summary
Shiftwork has been associated with elevated blood pressure (BP) and decreased heart-rate variability (HRV), two factors that may increase the long-term risk of cardiovascular disease mortality and morbidity (Furlan et al, 2000; Harrington, 1994; Knutsson et al, 1986; Taylor & Pocock, 1972; Tenkanen et al, 1997; Vrijkotte et al, 2000). The interference of circadian rhythm by shiftwork may increase psychosomatic, psychoneurotic, and gastrointestinal disorders (Axelsson et al, 2006; Moreno et al, 2006; Reinberg et al, 2007). Both HRV and BP are controlled by autonomic nervous system activity, which oscillates over the 24 h (Quan et al, 1997). Between 13% and 39% of twins are reported to have similar HRVs, but the percentage increases to 51% in times of stress. These studies suggest that people have their own basic patterns of HRV and BP (Boomsma et al, 1990; Busjahn et al, 1998; Degaute et al, 1994; Fava et al, 2005; Kupper et al, 2004; Singh et al, 1999; Sinnreich et al, 1999; Snieder et al, 1997)
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