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Biomedical subjects

Drew Dawson

Publications and source records attributed to Drew Dawson.

At least 19 recordsLinked to original sources
PubMed2007

Thermoregulatory changes around the time of sleep onset.

A causal relationship between declining nocturnal core temperature, increasing peripheral temperature, and sleep onset has been reported. The exact trigger for these thermoregulatory changes around sleep onset, however, is unknown. Our aim was to examine one possible trigger: prior knowledge of bedtime. Fourteen young, healthy male subjects (mean age+/-sem: 21.9+/-0.6 years), participated in a randomized, single-blind crossover study, where knowledge of bedtime was manipulated. Following a baseline night, subjects completed three experimental nights: (A) aware of bedtime; (B) no knowledge of bedtime; (C) misinformed about bedtime. In all conditions lights were turned off at each subject's habitual bedtime (determined from sleep diaries), to individually standardize the time of lights off. Polysomnography, rectal and peripheral (foot) temperatures were recorded continuously on each night. There was no significant difference in the time of sleep onset among conditions (mean+/-s.d.: 11:55 h+/-0.73 min), and in all conditions sleep onset occurred at the same rectal temperature. A significant difference in the temperature gradient between rectal and peripheral temperatures among the conditions was evident from 90 min to 40 min prior to sleep onset (P=0.05), with subjects achieving a more rapid rate of temperature change in the B and C condition relative to condition A. The present findings suggest that knowledge of bedtime may modulate changes in temperature around the time of sleep onset. It appears that there is an optimal core body temperature at which to initiate sleep, and changes in the rate of peripheral heat loss may assist in achieving this optimal temperature, and hence facilitate sleep onset.

Adult↗
PubMed2006

The relationship between the rate of melatonin excretion and sleep consolidation for locomotive engineers in natural sleep settings.

BACKGROUND: The aim of the study was to examine the role that melatonin production plays in the regulation of sleep consolidation in a population of shiftworkers working and sleeping in their natural environments. METHODS: 253 locomotive engineers (249 male, 4 female, mean age = 39.7 years) participated in the study for a 2-week period whilst working their normal roster patterns. Participants recorded details for all sleep periods in a sleep diary and collected urine samples during each day's main sleep period. The samples were subsequently assayed for the metabolite of melatonin in urine, 6-sulphatoxymelatonin (aMT6s), and the rate of excretion during main sleep periods was calculated. RESULTS: Separate one-way factorial ANOVAs revealed a significant effect of time of sleep onset on aMT6s excretion rate, sleep duration, and subjective sleep quality. Generally, the rate of aMT6s excretion was lower, sleep duration was shorter, and sleep quality was lower for sleeps initiated during the daytime than for sleeps initiated at night. CONCLUSION: Combined with previous studies linking melatonin production and sleep propensity, and others demonstrating the relationship between sleep consolidation and melatonin production in forced desynchrony protocols, the current results indicate that low production of melatonin may play a role in the poor consolidation of daytime sleep in natural sleep settings.

Journal Article↗
PubMed2006

Simulated train driving: fatigue, self-awareness and cognitive disengagement.

Fatigue is a serious issue for the rail industry, increasing inefficiency and accident risk. The performance of 20 train drivers in a rail simulator was investigated at low, moderate and high fatigue levels. Psychomotor vigilance (PVT), self-rated performance and subjective alertness were also assessed. Alertness, PVT reaction times, extreme speed violations (>25% above the limit) and penalty brake applications increased with increasing fatigue level. In contrast, fuel use, draft (stretch) forces and braking errors were highest at moderate fatigue levels. Thus, at high fatigue levels, errors involving a failure to act (errors of omission) increased, whereas incorrect responses (errors of commission) decreased. The differential effect of fatigue on error types can be explained through a cognitive disengagement with the virtual train at high fatigue levels. Interaction with the train reduced dramatically, and accident risk increased. Awareness of fatigue-related performance changes was moderate at best. These findings are of operational concern.

Awareness↗
PubMed2006

The suitability of a caffeinated energy drink for night-shift workers.

Past research has indicated that caffeinated 'functional energy drinks' (FEDs) are effective in counteracting sleepiness. It is not known however, what impact FEDs have on sleep itself. FEDs contain several active ingredients, including caffeine. They may therefore impact negatively on sleep and hence subsequent performance, deeming their use counterproductive. In a randomised cross-over design, 15 young adults participated in a simulated first night-shift protocol with 2 conditions, Functional Energy Drink (FED) and Non Functional Energy Drink (NonFED). Both involved a period of extended wakefulness (0700-0730 h-24.5 h) followed by an 8-h daytime 'recovery' sleep (0730-1530 h). During the FED condition, a commercially available FED was administered twice during the night. Sleepiness was assessed during the period of extended wakefulness and for a further 6h after waking. Sleep periods were recorded using a standard 5 channel polysomnogram. Comparison of the sleep periods showed that sleep onset latency remained unchanged as did stage 2 and slow wave sleep. Total sleep time however, was 29.1 min shorter (p<.05) in the FED condition. Sleep efficiency was also significantly reduced from 91.8+/-.9% to 84.7+/-2.7% (p<.05). It is evident that the residual effects of the FED's active ingredients impact on some aspects of daytime sleep following a simulated night-shift. Subsequent performance however was unaffected. The results deem FEDs to be effective for a single night-shift and warrant investigation into their use over successive night-shifts.

Adult↗
PubMed2006

A pilot study of the safety implications of Australian nurses' sleep and work hours.

The frequency and severity of adverse events in Australian healthcare is under increasing scrutiny. A recent state government report identified 31 events involving "death or serious [patient] harm" and 452 "very high risk" incidents. Australia-wide, a previous study identified 2,324 adverse medical events (AME) in a single year, with more than half considered preventable. Despite the recognized link between fatigue and error in other industries, to date, few studies of medical errors have assessed the fatigue of the healthcare professionals involved. Nurses work extended and unpredictable hours with a lack of regular breaks and are therefore likely to experience elevated fatigue. Currently, there is very little available information on Australian nurses' sleep or fatigue levels, nor is there any information about whether this affects their performance. This study therefore aims to examine work hours, sleep, fatigue and error occurrence in Australian nurses. Using logbooks, 23 full-time nurses in a metropolitan hospital completed daily recordings for one month (644 days, 377 shifts) of their scheduled and actual work hours, sleep length and quality, sleepiness, and fatigue levels. Frequency and type of nursing errors, near errors, and observed errors (made by others) were recorded. Nurses reported struggling to remain awake during 36% of shifts. Moderate to high levels of stress, physical exhaustion, and mental exhaustion were reported on 23%, 40%, and 36% of shifts, respectively. Extreme drowsiness while driving or cycling home was reported on 45 occasions (11.5%), with three reports of near accidents. Overall, 20 errors, 13 near errors, and 22 observed errors were reported. The perceived potential consequences for the majority of errors were minor; however, 11 errors were associated with moderate and four with potentially severe consequences. Nurses reported that they had trouble falling asleep on 26.8% of days, had frequent arousals on 34.0% of days, and that work-related concerns were either partially or fully responsible for their sleep disruption on 12.5% of occasions. Fourteen out of the 23 nurses reported using a sleep aid. The most commonly reported sleep aids were prescription medications (62.7%), followed by alcohol (26.9%). Total sleep duration was significantly shorter on workdays than days off (p < 0.01). In comparison to other workdays, sleep was significantly shorter on days when an error (p < 0.05) or a near error (p < 0.01) was recorded. In contrast, sleep was higher on workdays when someone else's error was recorded (p = 0.08). Logistic regression analysis indicated that sleep duration was a significant predictor of error occurrence (chi2 = 6.739, p = 0.009, e beta = 0.727). The findings of this pilot study suggest that Australian nurses experience sleepiness and related physical symptoms at work and during their trip home. Further, a measurable number of errors occur of various types and severity. Less sleep may lead to the increased likelihood of making an error, and importantly, the decreased likelihood of catching someone else's error. These pilot results suggest that further investigation into the effects of sleep loss in nursing may be necessary for patient safety from an individual nurse perspective and from a healthcare team perspective.

Adult↗
PubMed2006

Do short international layovers allow sufficient opportunity for pilots to recover?

For Australian pilots, short layovers (<40 h) are a feature of many international patterns. However, anecdotal reports suggest that flight crew members find patterns with short slips more fatiguing than those with a longer international layover, as they restrict the opportunity to obtain sufficient sleep. The current study aimed to determine whether pilots operating international patterns with short layovers have sufficient opportunity to recover prior to the inbound flight. Nineteen international pilots (ten captains, nine first officers) operating a direct return pattern from Australia to Los Angeles (LAX) with a short (n = 9) 9+/-0.8 h (mean+/-S.D) or long (n = 10) 62.2+/-0.9 h LAX layover wore an activity monitor and kept a sleep/duty diary during the pattern. Immediately before and after each flight, pilots completed a 5 min PalmPilot-based psychomotor vigilance task (Palm-PVT). Flights were of comparable duration outbound (3.5+/-0.6 h) and inbound (14.3+/-0.6 h) and timing. The amount of sleep obtained in-flight did not significantly vary as a function of layover length. However, pilots obtained significantly more sleep during the inbound (3.7+/-0.8 h) than the outbound flight (2.2+/-0.8 h). Pilots with the shorter layover obtained significantly less sleep in total during layover (14.0+/-2.7 h vs. 19.6+/-2.5), due to significantly fewer sleep periods (3.0+/-0.7 vs. 4.0+/-0.9). However, neither mean sleep duration nor the sleep obtained in the 24 h prior to the inbound flight significantly differed as a function of layover length. Response speed significantly varied across the pattern, and a significant interaction was also observed. For pilots with a short layover, response speed was significantly slower at the end of both the outbound and inbound flight, and prior to the inbound flight (i.e., at the end of layover), relative to response speed at the start of the pattern (pre-trip). Similarly, response speed for the longer layover was slower at the end of the outbound flight compared to pre-trip (approaching significance, p = 0.073). However, response speed at the beginning of the inbound flight was significantly faster than pre-trip and did not significantly differ from pre-trip at the end of the inbound flight. The data suggest that short slips (<40 h) do not allow pilots the opportunity to obtain sufficient sleep to reverse the effects of fatigue accumulated during the outbound flight. As a result, their response speed prior to the inbound flight is substantially slower than the response speed of flight crew with a longer layover.

Adult↗
PubMed2006

Can a shorter psychomotor vigilance task be used as a reasonable substitute for the ten-minute psychomotor vigilance task?

The 10 min psychomotor vigilance task (PVT) is commonly used in laboratory studies to assess the impact of sleep loss, sustained wakefulness, and/or time of day on neurobehavioral performance. In field settings, though, it may be impractical for participants to perform a test of this length. The aim of this study was to identify a performance measure that is sensitive to the effects of fatigue but less burdensome than a 10 min test. Sixteen participants (11 female, 5 male; mean age = 21.7 years) slept in the sleep laboratory overnight then remained awake for 28 h from 08:00 h. During every second hour, participants completed three PVTs of differing duration (10 min, 5 min, 90 sec). For the 5 min/10 min comparison, ANOVA indicated that response time was significantly affected by test length (F1,14 = 26.9, p < .001) and hours of wakefulness (F13,182 = 46.1, p < .001) but not by their interaction (F13,182 = 1.7, ns). There was a strong correlation between response time on the 5 and 10 min PVTs (r = .88, p < .001). For the 90 sec/10 min comparison, ANOVA indicated that response time was significantly affected by test length (F1,14 = 65.9, p < .001) and hours of wakefulness (F13,182 = 29.7, p < .001) as well as by their interaction (F13,182 = 6.0, p < .001). There was a strong correlation between response time on the 90 sec and 10 min PVTs (r = .77, p < .001). The effects of hours of wakefulness on neurobehavioral performance were similar for the 5 min and 10 min PVTs. In contrast, performance on the 90 sec PVT was less affected by hours of wakefulness than on the 10 min PVT. In addition, performance on the 10 min PVT was more highly correlated with the 5 min PVT than the 90 sec PVT. These data indicate that the 5 min PVT may provide a reasonable substitute for the 10 min PVT in circumstances where a test shorter than 10 min is required.

Adult↗
PubMed2006

Self-awareness of impairment and the decision to drive after an extended period of wakefulness.

Fatigue is an increasingly noted factor in road accidents. The ability to predict and be aware of impairment in terms of driving capability is important for potential legal liability and road safety. However, to date, there have been few studies that have investigated the accuracy of individuals in predicting how safely they could drive during conditions of sleep loss. Research has demonstrated that individuals rate themselves as better than the population average in a number of domains, including driving-related skills. Therefore, this study also aimed to investigate self-ratings of predicted driving ability during extended wakefulness and compare them to ratings made of a hypothetical other person under the same conditions. Thirty-two participants remained awake for a period of 40 h. Every 2 h, they completed the Psychomotor Vigilance Task (PVT) and rated on a seven-point scale how well they thought they could drive safely, react quickly in an emergency, and stay in their own lane. They were also asked to assess how they thought someone else in their own position could drive. The participants rated their driving ability as becoming significantly poorer at the same time that their PVT performance became significantly slower. Self-ratings indicating a qualitative assessment of poorer than neutral driving occurred at 03:00 h for both the "drive safely" and "react quickly" questions, after 19 h of continuous wakefulness (starting at 08:00 h). This occurred at 05:00 h for the "keep in my lane" question. Previous studies with a similar protocol demonstrated that under these conditions, individuals exhibit a performance decrements equivalent to someone with a blood alcohol concentration of 0.05% (the legal driving limit in Australia). Participants consistently rated the ability of others to drive as poorer than their own. The main implication from this study for road safety and legal liability is that it is reasonable to focus on a person's perception of the situation, as it does align with objective reality to a certain extent. A concern in terms of road safety is potential overconfidence, indicated by rating others consistently poorer than themselves.

Adolescent↗
PubMed2006

Train drivers' sleep quality and quantity during extended relay operations.

Relay operations are an important mode of freight transportation within Australia. Relay work requires multiple crews to drive the train continuously from one specified destination to another and return. Importantly, the nature of relay work requires train drivers to sleep on-board during designated resting shifts. The main aim of the present study was to investigate the quality and quantity of sleep obtained in on-board rest facilities (relay vans) during extended (four-day) relay operations. Drivers (n = 9) working the Port Augusta to Darwin relay operation volunteered to participate. The first leg of the trip typically took 40 h followed by an overnight stay in Darwin (between 8-12 h) prior to return. Two crews, each consisting of two drivers, changed every 8 h, giving the crew an 8 h rest in the relay van prior to each 8 h working shift. Using polysomnography, home sleep data were collected prior to and following each trip using a standard five-channel EEG montage. All sleep periods during the relay trip (including Darwin) were also recorded. Additionally, subjective sleep quality ratings were recorded following each sleep period. Analyses revealed that the quantity of sleep obtained in the relay vans (3.3 h) was significantly reduced compared to home (6.8 h). In general, the total sleep time was increased at night and reduced during the day. In terms of quality, sleep onset latency, sleep efficiency, and amount of slow wave and rapid eye movement sleep did not differ significantly between home and the relay vans. The results of the study highlight sleep quantity as the main concern during extended relay operations. Future research should focus on investigating the subjective and objective impact of this sleep reduction on waking functions.

Adult↗
PubMed2006

The sleep, subjective fatigue, and sustained attention of commercial airline pilots during an international pattern.

International commercial airline pilots may experience heightened fatigue due to irregular sleep schedules, long duty days, night flying, and multiple time zone changes. Importantly, current commercial airline flight and duty time regulations are based on work/rest factors and not sleep/wake factors. Consequently, the primary aim of the current study was to investigate pilots' amount of sleep, subjective fatigue, and sustained attention before and after international flights. A secondary aim was to determine whether prior sleep and/or duty history predicted pilots' subjective fatigue and sustained attention during the international flights. Nineteen pilots (ten captains, nine first officers; mean age: 47.42+/-7.52 years) participated. Pilots wore wrist activity monitors and completed sleep and duty diaries during a return pattern from Australia to Europe via Asia. The pattern included four flights: Australia-Asia, Asia-Europe, Europe-Asia, and Asia-Australia. Before and after each flight, pilots completed a 5 min PalmPilot-based psychomotor vigilance task (PVT) and self-rated their level of fatigue using the Samn-Perelli Fatigue Checklist. Separate repeated-measures ANOVAs were used to determine the impact of stage of flight and flight sector on the pilots' sleep in the prior 24 h, self-rated fatigue, and PVT mean response speed. Linear mixed model regression analyses were conducted to examine the impact of sleep in the prior 24 h, prior wake, duty length, and flight sector on pilots' self-rated fatigue and sustained attention before and after the international flights. A significant main effect of stage of flight was found for sleep in the prior 24 h, self-rated fatigue, and mean response speed (all p < 0.05). In addition, a significant main effect of flight sector on self-rated fatigue was found (p < .01). The interaction between flight sector and stage of flight was significant for sleep in the prior 24 h and self-rated fatigue (both p < .05). Linear mixed model analyses indicated that sleep in the prior 24 h was a significant predictor of self-rated fatigue and mean response speed after the international flight sectors. Flight sector was also a significant predictor of self-rated fatigue. These findings highlight the importance of sleep and fatigue countermeasures during international patterns. Furthermore, in order to minimize the risk of fatigue, the sleep obtained by pilots should be taken into account in the development of flight and duty time regulations.

Adult↗
PubMed2006

Predicting the timing and duration of sleep in an operational setting using social factors.

In recent years, there has been increasing interest in the use of bio-mathematical models to predict alertness, performance, and/or fatigue in operational settings. Current models use only biological factors to make their estimations, which can be limited in operational settings where social and geo-physical factors also dictate when sleep occurs. The interaction between social and biological factors that help determine the timing and duration of sleep during layover periods have been investigated in order to create and initially validate a mathematical model that may better predict sleep in the field. Participants were 32 male transmeridian airline pilots (17 captains, 10 first officers, and 5 second officers) flying the Sydney-Bangkok-London-Singapore-Sydney (SYD-LHR) pattern. Participants continued their regular schedule while wearing activity monitors and completing sleep and work diaries. The theoretical sleep timing model underpinning this analysis consists of separate formulations for short (<32 h) and long (>32 h) break periods. Longer break periods are split into three distinct phases-recovery (break start until first local night), personal (first local night until last local night), and preparation phases (last local night until break end)-in order to exploit potential differences specific to each. Furthermore, an iterative procedure combining prediction and retrodiction (i.e., using future duty timing information to predict current sleep timing) was developed to optimize predictive ability. Analysis found an interaction between the social and circadian sleep pressures that changed over the break period. Correlation analysis indicated a strong relationship between the actual sleep and new model's predictions (r = 0.7-0.9), a significant improvement when compared to existing models (r = 0.1-0.4). Social and circadian pressures play important roles in regulating sleep for international flight crews. An initial model has been developed in order to regulate sleep in these crews. The initial results have shown promise when applied to small sets of data; however, more rigorous validation must be carried out.

Adult↗
PubMed2006

Attenuated thermoregulatory response to mild thermal challenge in subjects with sleep-onset insomnia.

STUDY OBJECTIVES: To determine if heat loss capacity of sleep onset insomniacs was different from that of healthy sleepers. DESIGN: Measure skin temperature responses following brief exposure to a warm peripheral thermal challenge (PTC). SETTING: Sleep research laboratory in South Australia. PARTICIPANTS: Eight primary insomniacs with sleep onset insomnia according to DSM-IV-TR criteria (SOI; 5 male, 3 female; mean age +/- SEM = 35.2 +/- 4.2 years) and ten healthy sleeping control subjects (HS; 7 male, 3 female; mean age = 28.2 +/- 2.8 years). INTERVENTIONS: Two PTC conditions in counterbalanced order on non-consecutive days. During each condition, the subject's non-dominant forearm and hand were immersed for 3 minutes in Warm (45 degrees C) or Control water (i.e. same as the subject's non-dominant index finger temperature just prior to immersion, range 30-35 degrees C). MEASUREMENTS AND RESULTS: HS had a significantly higher maximum finger temperature response after immersion than SOI (P < 0.05). Expressed relative to Control PTC temperatures, the Warm PTC caused a significant increase in mean finger temperature for HS of 4.1 +/- 0.8 degrees C, compared with SOI of 0.9 +/- 0.4 degrees C. A significant negative relationship was observed between maximum finger temperature response and self-reported sleep onset latencies (R = -0.57, P < 0.05). There were no main effects of sleep status (SOI vs. HS) or interactions by time, in skin temperatures measured at either the back of hands or feet. CONCLUSIONS: SOI were observed to have significantly attenuated thermoregulatory responses to a mild positive thermal challenge, providing evidence that impaired heat loss capacity from the periphery is associated with sleep onset insomnia.

Adult↗
PubMed2006

Layover sleep prediction for cockpit crews during transmeridian flight patterns.

INTRODUCTION: Current models of fatigue and alertness use a combination of biological (circadian) and homeostatic factors to predict sleep and wake. Such models do not include social factors in their calculations. The aim of our analysis was to compare the relative contributions of social and biological factors in models designed to predict the total sleep time (TST) during layover periods between transmeridian flights. METHOD: The study actigraphically collected sleep information from 86 cockpit crew (mean age 46.7 yr, SD 4.3 yr) during round-trip patterns from Australia to Los Angeles (n=15), Europe (n=42), New York (n=10), and Hong Kong (n=19). Linear regression models were constructed to predict TST using data from airline schedules. This schedule information included layover length, flight duration, the number of night hours at the destination (social hours), the number of night hours in Australian Eastern Standard time (biological hours), and time zone displacement. These models were then validated using independent data. RESULTS: Analysis indicated that the schedule data was highly correlated. Linear regression analyses indicated that social night hours account for more variance than biological night hours (r = 0.8 vs. 0.7). Additionally, the layover length achieved a correlation coefficient of 0.9. These results were strengthened when the model parameters were applied to the cross-validation dataset. DISCUSSION: Social night hours significantly influence sleep during international layovers and may be a better predictor than biological night hours. More research must be carried out to determine the validity of these findings in a larger, randomly collected flight sample.

Aerospace Medicine↗
PubMed2005

Train drivers' sleep and alertness during short relay operations.

Within Australia, there has been a recent expansion of relay working operations. To address concerns about the amount of sleep obtained by drivers in relay vans, and potential deficits in alertness associated with relay work, the current study assessed the sleep behaviour and alertness of 15 train drivers working short (<48 h) relay operations. In total, drivers obtained 8-12h of sleep during the relay trip (which took approx 40 h). Overall, they reported that they felt more alert following each sleep period. Drivers were able to sustain attention during the 10-min vigilance tasks administered before and after each shift. These findings suggest that the amount of sleep obtained in crew vans during short relay operations is sufficient to maintain alertness during the trip. They also emphasise the importance of scheduling shifts to maximise the number of sleep opportunities that occur between 2200 and 0700 h.

Adult↗
PubMed2005

Melatonin as a hypnotic: con.

The physiological roles of melatonin are still unclear despite almost 50 years of research. Elevated melatonin levels from either endogenous nocturnal production or exogenous daytime administration are associated in humans with effects including increased sleepiness, reduced core temperature, increased heat loss and other generally anabolic physiological changes. This supports the idea that endogenous melatonin increases nocturnal sleep propensity, either directly or indirectly via physiological processes associated with sleep. The article "Melatonin as a hypnotic--Pro", also in this issue, presents evidence to support this viewpoint. We do not entirely disagree, but nevertheless feel this is an overly simplistic interpretation of the available data. Our interpretation is that melatonin is primarily a neuroendocrine transducer promoting an increased propensity for 'dark appropriate' behavior. Thus, it is our view that exogenous melatonin is only hypnotic in those species or individuals for which endogenous melatonin increases sleep propensity and is consequently a dark appropriate outcome. Evidence supporting this position is drawn primarily from studies of exogenous administration of melatonin and its varied effects on sleep/wake behavior based on dose, time of administration, age and other factors. From this perspective, it will be shown that melatonin can exert hypnotic-like effects but only under limited circumstances.

Animals↗