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Drew Dawson

Publications and source records attributed to Drew Dawson.

At least 37 records · Page 2Linked to original sources
PubMed2005

Managing fatigue: it's about sleep.

Fatigue has increasingly been viewed by society as a safety hazard. This has lead to increased regulation of fatigue by governments. The most common control process has been compliance with prescriptive hours of service (HOS) rule sets. Despite the frequent use of prescriptive rule sets, there is an emerging consensus that they are an ineffective hazard control, based on poor scientific defensibility and lack of operational flexibility. In exploring potential alternatives, we propose a shift from prescriptive HOS limitations toward a broader Safety management system (SMS) approach. Rather than limiting HOS, this approach provides multiple layers of defence, whereby fatigue-related incidents are the final layer of many in an error trajectory. This review presents a conceptual basis for managing the first two levels of an error trajectory for fatigue. The concept is based upon a prior sleep/wake model, which determines fatigue-risk thresholds by the amount of sleep individuals have acquired in the prior 24 and 48 h. In doing so, managing level 1 of the error trajectory involves the implementation of systems that determine probabilistic sleep opportunity, such as prescriptive HOS rules or fatigue modelling. Managing level 2, requires individuals to be responsible for monitoring their own prior sleep and wake to determine individual fitness for duty. Existing subjective, neurobehavioral and electrophysiological research is reviewed to make preliminary recommendations for sleep and wake thresholds. However, given the lack of task- and industry-specific data, any definitive conclusions will rely in post-implementation research to refine the thresholds.

Accidents, Occupational↗
PubMed2005

The impact of extended leave on sleep and alertness in the Australian rail industry.

In the past, scientific studies have investigated the effects of shift timing and duration on sleep and alertness in the rail industry. To our knowledge no research has been conducted to determine the effects of extended break lengths (>48 h) on these factors. Hence, this study analyses the work and rest schedules of 304 Australian rail employees (mean age 41.3 yr, standard deviation 7.4 yr) to determine the effect of prior break lengths (12-169 h) on sleep and subjective alertness at work after periods of leave. Extended break periods (>48 h) were found to increase the length of the sleep prior to returning to work and reduce the total wake time to the end of the first shift, but did not influence levels of subjective alertness immediately prior to the commencement of the first shift. Research into the influence of longer break periods (>169 h) is needed in order to make definitive conclusions regarding sensible return to work policies after extended leave within the Australian rail industry.

Adult↗
PubMed2005

The impact of sustained wakefulness and time-of-day on OSPAT performance.

Fatigue associated with shiftwork is a key contributor to human error in the workplace. One way to prevent fatigue-related errors from occurring is to identify fatigue in employees using fitness-for-duty measures. The Occupational Safety Performance Assessment Test (OSPAT), an unpredictable tracking task that measures hand-eye coordination, is currently being used as a fitness-for-duty measure in a variety of industries, but has not yet been validated as a test sensitive to the effects of fatigue. Consequently, the aim of this study was to systematically examine the impact of sustained wakefulness and time-of-day on OSPAT performance. Twenty individuals (10 male, 10 female), aged between 18-25 yr (M=20.90, SD=2.29) participated in the study, which was conducted in Australia. The study had a repeated measures design, whereby participants completed the OSPAT and measures of sustained attention (i.e., the psychomotor vigilance task: PVT), and subjective alertness (i.e., the Visual Analog Scale: VAS) every 2 h during 24 h of sustained wakefulness, beginning at 07:00 h. Results revealed that VAS ratings of alertness, PVT performance, and OSPAT performance declined significantly as hours of wakefulness increased during the night-time (all p<.01). Furthermore, a positive correlation between OSPAT and PVT performance was observed (r=0.40, p<.01). Overall, these findings suggest that OSPAT is sensitive to sustained wakefulness during the night-time, and builds the case for OSPAT being a suitable measure for determining fitness-for-duty in workplace environments.

Adolescent↗
PubMed2005

Changes in the concentration of urinary 6-sulphatoxymelatonin during a week of simulated night work.

The aim of the study was to examine the adaptation of participants to a common night work schedule using urinary 6-sulphatoxymelatonin (aMT6s) concentration as the circadian phase marker. Fifteen adults (7 male, 8 female, age = 21.9 yr) spent nine consecutive nights in the laboratory, including: (i) adaptation sleep, (ii) baseline sleep, and (iii) seven simulated night shifts (23:00-07:00 h) followed by daytime sleep. During the baseline and daytime sleeps, participants collected urine samples which were subsequently assayed for aMT6s. The concentration of aMT6s in urine for the first three day sleeps was significantly lower than for the baseline sleep, but there was no difference in aMT6s concentrations between any of the last three day sleeps and the baseline sleep. The data indicate that people may adapt to a pattern of work that includes seven consecutive night shifts if they adhere to a fixed sleep schedule, if their exposure to morning sunlight is minimised, and if they are provided with an ideal sleep environment.

Adaptation, Physiological↗
PubMed2005

How well do train driver's sleep in relay vans?

Relay working operations typically require two crews of train drivers to work a rotating 8-h schedule for two or more days. While one crew is driving, the other has the opportunity to sleep onboard the train. The current study investigated the impact of relay work on drivers sleep quantity and quality. Fourteen drivers wore wrist activity monitors and completed sleep/wake diaries for 3 d prior to and during short (<48 h) relay trips. Drivers obtained an average of 7.8 h sleep per night while at home, and an average of 4 h sleep per opportunity during the relay trip. Sleep obtained in the relay van was associated with longer sleep onset latencies, lower efficiency and poorer subjective quality than sleep at home. During the relay trip, drivers obtained significantly more sleep during opportunities that occurred in the evening, than those that occurred early morning or during the day. These findings suggest that while drivers are able to obtain sleep during short relay operations, it is of poorer quality than sleep obtained at home. Further, the timing of the sleep opportunities during the relay trip impacts on the quantity and quality of sleep obtained.

Adult↗
PubMed2005

Fatigue assessment in the field: validation of a hand-held electronic psychomotor vigilance task.

INTRODUCTION: In recent years, there has been an increasing need for a reliable and practical tool for assessing fatigue-related impairment in the field. This study investigated the sensitivity of one potential tool, a 5-min version of the psychomotor vigilance task (PVT) specifically designed for use on personal digital assistants (PDA), to 28 h of sustained wakefulness. METHODS: There were 15 participants who slept in the laboratory overnight then remained awake from 08:00 (Day 1) to 12:00 (Day 2). During every second hour, they completed a 10-min PVT, a sustained attention task that is sensitive to the effects of sleep loss and fatigue, and a 5-min PDA-PVT. RESULTS: While performance on both tasks significantly varied as a function of hours of wakefulness, responses on the PDA-PVT were typically slower than on the PVT. When performance scores were standardized, the negative impact of increasing hours of wakefulness on performance on the 5-min PDA-PVT and 10-min PVT did not significantly differ. DISCUSSION: The findings suggest that the 5-min PDA-PVT may provide a reasonable substitute for the 10-min PVT, particularly in circumstances where a shorter test is required and/or the standard PVT is not as practical.

Adolescent↗
PubMed2004

Shiftwork experience and the value of time.

Dissatisfaction with shiftwork has been shown to increase with age and work experience. The objective was to determine if differences in preferred paid work time existed between shiftworkers with different lengths of shiftwork experience and age-matched non-shiftworkers (controls). A questionnaire was used to determine how controls and shiftworkers with different shiftwork experience perceived the value of preferred work time across the week. Participants were required to value each hour across the days of the week on a scale from 0 (least preference) to 10 (highest preference). Data were analysed across groups to produce mean and standard deviation matrices. Unpaired t-tests determined significant differences between groups. This study found that preferred hours-of-work change with years of shiftwork experience. For shiftworkers in their first 5 years and those in their 30th-year-plus of shiftwork, night work was a low priority. Shiftworkers with 17 - 30 years experience indicated a preference for work any time across the week. Overall, shiftworkers extended their preferred work hours to include the evenings and weekend. Controls adhered more strongly to current societal norms. The results suggest that a person initially undertaking shiftwork may well be one with a less restrictive perception of time and its use, however, this perception may alter over time.

Adult↗
PubMed2004

Adaptation of performance during a week of simulated night work.

This study aimed to provide a comparative index of the performance impairment associated with the fatigue levels frequently experienced in workplaces that require night work. To do this, we equated fatigue-related impairment with the impairment resulting from varying levels of alcohol intoxication. Fifteen young individuals participated in two counterbalanced conditions which required them to (1). 'work' seven consecutive 8-h night shifts, and (2). consume an alcoholic beverage at hourly intervals until their blood alcohol concentration (BAC) reached 0.10%. In each condition, performance was measured at hourly intervals using a 10-min psychomotor vigilance task (PVT). Analysis indicated that as BAC increased, performance impairment significantly increased. Similarly, response times significantly increased during the first six simulated night-shifts, and lapse frequency significantly increased during the first two shifts. Equating the two conditions indicated that the first simulated night shift was associated with the greatest degree of performance impairment. In general, the impairment at the end of this shift was greater than that observed at a BAC of 0.10%. During the second and third simulated night shifts, the performance impairment was less than on the first night, but greater than that observed at a BAC of 0.05%. For the final four nights, the performance decrements generally did not exceed those observed at a BAC of 0.05%. This suggests that during a week of consecutive night shifts, adaptation of performance occurs.

Adolescent↗
PubMed2004

Thermoregulation as a sleep signalling system.

Temperature and sleep are interrelated processes. Under normal environmental conditions, the rhythms of core body temperature Tc and sleep propensity vary inversely across the day and night in healthy young adults. Although this relationship has drawn considerable interest, particularly in recent years, it is still not known whether this relationship is causative or merely coincidental. As somnogenic brain areas contain thermosensitive cells, it is possible that the sleep/wake cycle may be directly affected by thermoregulatory changes themselves. That is, that changes in temperature may trigger, either directly or indirectly, somnogenic brain areas to initiate sleep. There is now an emerging body of evidence from both physiological and neuroanatomical studies to indicate that this may indeed be the case. This paper will examine the literature relating to this relationship and propose a model where thermoregulatory changes provide an additional signal to the brain regions that regulate sleep and wakefulness. The model attempts to explain how temperature changes before and after sleep onset act in a positive feedback loop to maintain a consolidated sleep bout.

Body Temperature↗
PubMed2004

The validity of psychomotor vigilance tasks of less than 10-minute duration.

The 10-min psychomotor vigilance task (PVT) has often been used to assess the impact of sleep loss on performance. Due to time constraints, however, regular testing may not be practical in field studies. The aim of the present study was to examine the suitability of tests shorter than 10 min. in duration. Changes in performance across a night of sustained wakefulness were compared during a standard 10-min PVT, the first 5 min of the PVT, and the first 2 min of the PVT. Four performance metrics were assessed: (1) mean reaction time (RT), (2) fastest 10% of RT, (3) lapse percentage, and (4) slowest 10% of RT. Performance during the 10-min PVT significantly deteriorated with increasing wakefulness for all metrics. Performance during the first 5 min and the first 2 min of the PVT deteriorated in a manner similar to that observed for the whole 10-min task, with all metrics except lapse percentage displaying significant impairment across the night. However, the shorter the task sampling time, the less sensitive the test is to sleepiness. Nevertheless, the 5-min PVT may provide a viable alternative to the 10-min PVT for some performance metrics.

Adolescent↗
PubMed2004

A model to predict work-related fatigue based on hours of work.

Several research groups have developed models for estimating the work-related fatigue associated with shiftworkers' duty schedules. In June 2002, invited members of seven of these groups attended the Fatigue and Performance Modeling Workshop in Seattle, WA. At the workshop, each group described the background and conceptual basis of their model, and an independent party compared the models' predictions with performance and sleepiness data from five laboratory- and workplace-based scenarios. One of these models, the Fatigue Audit InterDyne (FAID), can be used to quantify the work-related fatigue associated with any duty schedule using hours of work (i.e., start/end times of work periods) as the sole input. The objectives of the current paper were to: 1) describe the background and conceptual basis of FAID; 2) present FAID-based predictions for four of the scenarios; and 3) discuss the advantages of, and possible improvements to, FAID. The analyses conducted to compare the predictive power of each model are described in detail by Van Dongen elsewhere in this issue.

Circadian Rhythm↗
PubMed2003

The ability to self-monitor performance during a week of simulated night shifts.

STUDY OBJECTIVES: Research has indicated that individuals are able to accurately monitor the performance decrements they experience during unitary periods of acute sleep deprivation. The aim of the current study was to investigate the ability to self-monitor performance during a week of simulated night shifts. DESIGN: Subjects completed 7 consecutive 8-hour night shifts (11 pm-7 am). SETTING: University sleep laboratory. SUBJECTS: Fifteen young (7 men, 8 women, 19-25 years) healthy volunteers. INTERVENTIONS: During the night shifts, performance was measured hourly on 4 performance parameters: psychomotor vigilance test (PVT), tracking, and grammatical reasoning (GRG) accuracy and response latency. Before and after each test, subjects completed visual analogue scales, which required them to rate their alertness and their performance speed and/or accuracy. RESULTS: Analysis indicated that GRG response latency and tracking were significantly impaired (P<0.05) during the first 2 shifts only. The PVT performance displayed consistent impairment, with significant (P<0.05) declines during all but the final shift. The pattern of deterioration in subjective ratings of alertness was similar to that of the PVT data. Correlations between subjective alertness and self-ratings of performance were significant (P<0.01) for all parameters (r=0.39-0.69). Significant (P<0.05) correlations were found across the week between pretest performance ratings and actual performance for all parameters except GRG accuracy (r=0.29-0.58) and between posttest ratings and actual performance for all parameters (r=0.52-0.75). Correlations between pretest ratings and actual performance were also conducted separately for each shift. Highest correlations were found during the first shift, with r-values that were low for GRG accuracy (r=0.32) and GRG response latency (r=0.20), moderate for tracking (r=0.41), and high for PVT (r=0.82). In general, lower correlations were found later in the week. CONCLUSIONS: Overall, results indicate that individuals have only a moderate ability to predict performance impairment during a week of night shifts. It is likely that performance ratings are based, at least to a certain extent, on subjective alertness levels. Furthermore, it seems that rating accuracy is improved on tasks providing performance feedback, such as the PVT. Finally, it appears that after testing, individuals have a more accurate perception of their performance.

Acute Disease↗
PubMed2003

A sedentary day: effects on subsequent sleep and body temperatures in trained athletes.

Exercise effects on sleep in fit healthy people have been difficult to determine because their sleep is close to optimal, leaving little room for improvement. Another method for assessing exercise effects on sleep is to significantly reduce the degree of activity in highly active people. Fifteen trained athletes who exercised daily at a moderate to high intensity were employed. By requesting that subjects remain sedentary in the laboratory for an entire day, the effect of reduced exercise on subsequent sleep parameters was assessed. Sleep and temperature were recorded after a sedentary day and after a normal day of moderate to high activity (control condition) in a counterbalanced design. In the sedentary condition, slow-wave sleep (SWS) decreased by a mean of 15.5+/-7.0 min and slow-wave activity (SWA) differed significantly (P<.05) between conditions in the first hour of sleep only. Rapid eye movement (REM) sleep increased by a mean of 17.9+/-5.7 min in the sedentary condition, while sleep onset latency (SOL) to Stages 1 and 2 increased by 10.2 and 10.7 min, respectively, and REM sleep latency decreased by 24.0+/-6.8 min (all P<.05). Between conditions, there was no overall effect on total sleep time (TST), sleep efficiency, wake after sleep onset or core or foot temperatures (P>.05). With reduced exercise load, SWS pressure may have been reduced, resulting in lower levels of SWS and increased REM sleep. Thus, the data indicate that reducing exercise has significant effects on sleep that may have implications for athletes tapering for competition.

Adult↗
PubMed2003

Neurobehavioural performance effects of daytime melatonin and temazepam administration.

Exogenous melatonin is a potential treatment for circadian disruption and insomnia. Hence, it is important to determine and quantify neurobehavioural performance effects associated with its use. The present study compared neurobehavioural performance following administration of melatonin and the benzodiazepine temazepam, using a within-subjects design. Following a training day, 16 healthy, young subjects (six males, 10 females; mean age +/- SEM, 21.4 +/- 6 years) participated in a 3-day protocol. After sleeping overnight in the laboratory, subjects completed a battery of tests at hourly intervals between 08:00 and 11:00 hours and at two hourly intervals between 13:00 and 17:00 hours. The neurobehavioural performance tasks included: unpredictable tracking, spatial memory, vigilance and logical reasoning. Subjective sleepiness was measured at hourly intervals using a visual analogue scale. At 12:00 h subjects were administered a capsule containing 5 mg melatonin, 10 mg temazepam or placebo, in a randomized, double-blind crossover fashion. A significant drug x time interaction was evident on the unpredictable tracking, spatial memory and vigilance tasks (P < 0.05). Greater changes in performance were evident following temazepam administration than melatonin administration, relative to placebo. Administration of melatonin or temazepam significantly elevated subjective sleepiness levels, relative to placebo (P </= 0.05). The present findings demonstrate that melatonin administration induces a smaller deficit in performance on a range of neurobehavioural tasks than temazepam. Given melatonin's soporific and chronobiotic properties, these results suggest that melatonin may be preferable to benzodiazepines in the management of circadian and sleep disorders.

Adult↗
PubMed2003

Comparison of digital infrared thermal imaging (DITI) with contact thermometry: pilot data from a sleep research laboratory.

Body temperature regulation is associated with changes in sleep propensity; therefore, sleep research often necessitates concomitant assessment of core and skin surface temperatures. Attachment to thermistors may limit the range of movement and comfort, introducing a potential confound that may prolong sleep initiation or increase wakefulness after sleep onset. It has been suggested that contact thermometry may artificially increase temperatures due to insulation. We report here on a method of remote sensing skin temperatures using a digital infrared thermal imaging (DITI) system, which can reduce these potential confounds. Using data from four healthy young adult volunteers (age = 26.8 +/- 2.2 years; mean +/- SEM), we compared measures of skin temperature using a DITI system with contact thermometry methods already in use in our sleep laboratory. A total of 416 skin temperature measurements (T(sk)) were collected from various sites, resulting in an overall correlation coefficient of R = 0.99 (p < 0.0001) between both methods. Regression analyses for individuals resulted in correlation coefficients between 0.80 and 0.97. These pilot results suggest that DITI can assess skin surface temperatures as accurately as contact thermometry, provided the interest is in relative and not absolute temperature changes. This and some other important limitations are discussed in more detail hereafter.

Adult↗
PubMed2003

The relationship between the dim light melatonin onset and sleep on a regular schedule in young healthy adults.

The endogenous melatonin onset in dim light (DLMO) is a marker of circadian phase that can be used to appropriately time the administration of bright light or exogenous melatonin in order to elicit a desired phase shift. Determining an individual's circadian phase can be costly and time-consuming. We examined the relationship between the DLMO and sleep times in 16 young healthy individuals who slept at their habitual times for a week. The DLMO occurred about 2 hours before bedtime and 14 hours after wake. Wake time and midpoint of sleep were significantly associated with the DLMO (r = 0.77, r = 0.68 respectively), but bedtime was not (r = 0.36). The possibility of predicting young healthy normally entrained people's DLMOs from their sleep times is discussed.

Adult↗