Cardiac autonomic activity during simulated shift work

Abstract

Shift work leads to adverse health outcomes including increased risk of cardiovascular disease. Heart rate (HR) and heart rate variability (HRV) are measures of cardiac autonomic activity and markers of cardiovascular disease and mortality. To investigate the effects of shift work on cardiac autonomic activity, we assessed the influence of simulated night work on HR and HRV, and dissociated the direct effects of circadian misalignment from those of sleep displacement and altered physical activity patterns. A total of 29 subjects each participated in one of two in-laboratory, simulated shift work studies. In both studies, EKG was continuously monitored via Holter monitors to measure HR and the high frequency (HF) component of HRV (HF-HRV). We found endogenous circadian rhythmicity in HR and HF-HRV. Sleep and waking physical activity, both displaced during simulated night work, had more substantial, and opposite, effects on HR and HF-HRV. Our findings show systematic but complex, interacting effects of time of day, sleep/wake state, and physical activity on cardiac autonomic activity. These effects need to be taken into account when evaluating HR and HRV in shift work settings and when interpreting these measures of cardiac autonomic activity as markers of cardiovascular disease.

Night shift schedule alters endogenous regulation of circulating cytokines

“…Digital sleep records were visually scored according to contemporaneous American Academy of Sleep Medicine standards ( Iber et al, 2007 ). As previously reported, the night shift condition involved no substantive sleep loss or sleep disorder and had minimal effect on the central circadian pacemaker ( Skene et al, 2018 ; Skornyakov et al, 2019 ). During this timetable of sleep/wake, meals were provided at 1.5 (breakfast), 7 (lunch), and 13.5 (dinner) h of scheduled wakefulness, and illuminance set below 50 lux during scheduled wakefulness.…”

“…In this highly controlled laboratory study of healthy young adults, we found that circadian misalignment from simulated night shift altered the endogenous 24-h patterns of circulating cytokines. As the night shift condition involved no significant sleep loss ( Skene et al, 2018 ), resulted in no substantive alteration in sleep quality ( Skornyakov et al, 2019 ) and had minimal effect on the central circadian pacemaker ( Fig. 2 , top right), these results indicate imbalance in the endogenous regulation of cytokines after the night shift schedule, free of the influence of bright light.…”

Night shift schedule causes circadian dysregulation of DNA repair genes and elevated DNA damage in humans

“…There were no material differences in results; therefore, the results of the more parsimonious original cosinor analysis were retained. The presence of circadian rhythmicity was evaluated by t ‐test ( P < .05) of the circadian amplitude 49 . Here, we were most concerned with type II error (ie, falsely claiming the absence of circadian rhythmicity) and therefore did not correct the type I error threshold for multiple comparisons 50 .…”

“…The presence of circadian rhythmicity was evaluated by t-test (P < .05) of the circadian amplitude. 49 Here, we were most concerned with type II error (ie, falsely claiming the absence of circadian rhythmicity) and therefore did not correct the type I error threshold for multiple comparisons. 50 Differences in circadian parameters between the simulated day and night shift conditions were evaluated using planned contrasts (t-tests, P < .05).…”

Circulating Exosomal miRNAs Signal Circadian Misalignment to Peripheral Metabolic Tissues

“…Linear regression was applied to estimate differences between conditions and reference values. Cosinor analyses to investigate 24-h rhythmicity were performed using non-linear mixed-effects regression [ 113 , 114 ], implemented in SAS version 9.4 (SAS Institute, Cary, NC, USA). Comparisons between conditions for cosinor analysis were based on planned contrasts, implemented as t-tests of the difference in parameter estimates between conditions against zero.…”