Documents Ferguson, Sally A. 3 results

"Objective
This study aimed to investigate sleep and circadian phase in the relationships between neurobehavioral performance and the number of consecutive shifts worked.
Methods
Thirty-four shift workers [20 men, mean age 31.8 (SD 10.9) years] worked 2–7 consecutive night shifts immediately prior to a laboratory-based, simulated night shift. For 7 days prior, participants worked their usual shift sequence, and sleep was assessed with logs and actigraphy. Participants completed a 10-minute auditory psychomotor vigilance task (PVT) at the start (~21:00 hours) and end (~07:00 hours) of the simulated night shift. Mean reaction times (RT), number of lapses and RT distribution was compared between those who worked 2–3 consecutive night shifts versus those who worked 4–7 shifts.
Results
Following 4–7 shifts, night shift workers had significantly longer mean RT at the start and end of shift, compared to those who worked 2–3 shifts. The slowest and fastest 10% RT were significantly slower at the start, but not end, of shift among participants who worked 4–7 nights. Those working 4–7 nights also demonstrated a broader RT distribution at the start and end of shift and had significantly slower RT based on cumulative distribution analysis (5th, 25th, 50th, 75th percentiles at the start of shift; 75th percentile at the end of shift). No group differences in sleep parameters were found for 7 days and 24 hours prior to the simulated night shift.
Conclusion
A greater number of consecutive night shifts has a negative impact on neurobehavioral performance, likely due to cognitive slowing."

"The purpose of the current study was to investigate the impact of work- and sleep-related factors on an objective measure of response time in a field setting. Thirty-five mining operators working 12-h shift patterns completed daily sleep and work diaries, wore activity monitors continuously and completed palm-based psychomotor vigilance tests (palmPVT) at the start and end of each shift. Linear mixed models were used to test the main effects on response time of roster, timing of test, sleep history and prior wake. The time at which the test occurred was a significant predictor of response time (F3,403.4 = 6.72, p < .01) with the end of night shifts being associated with significantly slower response times than the start of night shifts, and the start or end of day shifts. Further, the amount of sleep obtained in the 24 h prior to the test was also a significant predictor of response time (F3,407.0 = 3.05, p < .01). The results suggest that, as expected, the end of night shift is associated with changes in response time indicative of performance impairments. Of more interest however is that immediate sleep history was also predictive of changes in response time with lower amounts of prior sleep related to slower response times. The current data provides further evidence that sleep is a primary mediator of performance, independent of roster pattern."

"A number of studies have described mood change during sleep loss in the laboratory, however, an understanding of fluctuations in structural aspects of mood under such conditions is lacking. Sixty-two healthy young adults completed one of three possible conditions: one (n = 20) or two (n = 23) nights of sleep loss or the control condition which consisted of one (n = 9) or two (n = 10) nights of 9 h time in bed. The Mood Scale II was completed every two waking hours and data were analysed in terms of the frequency and intensity of mood reports. Overall, sleep loss conditions were associated with significantly less frequent happiness and activation and more frequent fatigue reports (p < 0.001). Intensity was also significantly reduced for activation and happiness, and increased for depression, anger and fatigue (p < 0.05). Interestingly, there were no significant differences in anger following two nights in the laboratory with or without sleep. Further, two nights in the lab with normal sleep was associated with significant increases in depression intensity (p < 0.05). Findings support the hypothesis of a mood regulatory function of sleep and highlight the relative independence of frequency and intensity and of positive and negative mood dimensions. Findings also suggest that the laboratory environment, in the absence of sleep loss, may have a significant negative impact on mood."