Guillaume Chaumet

Extended Driving Impairs Nocturnal Driving Performances

Though fatigue and sleepiness at the wheel are well-known risk factors for traffic accidents, many drivers combine extended driving and sleep deprivation. Fatigue-related accidents occur mainly at night but there is no experimental data available to determine if the duration of prior driving affects driving performance at night. Participants drove in 3 nocturnal driving sessions (3–5am, 1–5am and 9pm–5am) on open highway. Fourteen young healthy men (mean age [±SD] = 23.4 [±1.7] years) participated Inappropriate line crossings (ILC) in the last hour of driving of each session, sleep variables, self-perceived fatigue and sleepiness were measured. Compared to the short (3–5am) driving session, the incidence rate ratio of inappropriate line crossings increased by 2.6 (95% CI, 1.1 to 6.0; P<.05) for the intermediate (1–5am) driving session and by 4.0 (CI, 1.7 to 9.4; P<.001) for the long (9pm–5am) driving session. Compared to the reference session (9–10pm), the incidence rate ratio of inappropriate line crossings were 6.0 (95% CI, 2.3 to 15.5; P<.001), 15.4 (CI, 4.6 to 51.5; P<.001) and 24.3 (CI, 7.4 to 79.5; P<.001), respectively, for the three different durations of driving. Self-rated fatigue and sleepiness scores were both positively correlated to driving impairment in the intermediate and long duration sessions (P<.05) and increased significantly during the nocturnal driving sessions compared to the reference session (P<.01). At night, extended driving impairs driving performances and therefore should be limited.

Sleepiness, near-misses and driving accidents among a representative population of French drivers

Study objectives were to determine the prevalence of sleepy driving accidents and to explore the factors associated with near‐miss driving accidents and actual driving accidents in France. An epidemiological survey based on telephone interviews was conducted on a representative sample of French drivers. The questionnaire included sociodemographics, driving and sleep disorder items, and the Epworth sleepiness scale. Of 4774 drivers (response rate: 86%), 28% experienced at least one episode of severe sleepiness at the wheel (i.e. requiring to stop driving) in the previous year; 11% of drivers reported at least one near‐miss accident in the previous year (46% sleep‐related); 5.8% of drivers reported at least one accident, 5.2% of these being sleep related (an estimate of 90 000 sleep‐related accidents per year in France). Sleepy driving accidents occurred more often in the city (53.8%), during short trips (84.6%) and during the day (84.6%). Using logistic regression, the best predictive factor for near‐misses was the occurrence of at least one episode of severe sleepiness at the wheel in the past year [odds ratio (OR) 6.50, 95% confidence interval (CI), 5.20–8.12, P < 0.001]. The best predictive factors for accidents were being young (18–30 years; OR 2.13, 95% CI, 1.51–3.00, P < 0.001) and experiencing at least one episode of severe sleepiness at the wheel (OR 2.03, 95% CI, 1.57–2.64, P < 0.001). Sleepiness at the wheel is a risk factor as important as age for traffic accidents. Near‐misses are highly correlated to sleepiness at the wheel and should be considered as strong warning signals for future accidents.

Confinement and sleep deprivation effects on propensity to take risks

INTRODUCTION The impact of confinement and sleep deprivation on risk-taking propensity is a key issue in crew management. We investigated both confinement and gender effects on risk propensity and performance during up to 36 h of extended wakefulness. METHOD We studied 4 groups of 3 men and 3 women [N = 24, mean age (+/- SD) = 32.9 +/- 5.8 yr] for 10 consecutive days: a 7-d confined period (CONF) or a 7-d baseline (BASE) condition preceding one control night of normal sleep, one night of sleep deprivation, and one recovery night in the laboratory. Risk propensity (EVAR scale) and simple reaction time task (SRTT) performances were monitored every 2.25 h (0930-1945) during CONF and every 2.11 h (0930-0745) during the sleep deprivation condition. RESULTS Overall risk propensity during extended wakefulness showed a variation in both conditions with two diurnal peaks separated by a nocturnal minima. After the confinement period, no second peak was found. Number of lapses (reaction time > 500 ms) on the SRTT varied daily in both conditions. In the normal sleep schedule, subjects increased their level of impulsiveness between the first day and the end of confinement (P < 0.05). DISCUSSION During the night of sleep deprivation, risk-taking propensity decreases and remains stable the following day in the confinement condition while it increases after the baseline period. In a confined environment under a normal sleep-wake schedule, impulsiveness increases in men and women.

Time Course of Neurobehavioral Alertness During Extended Wakefulness in Morning- and Evening-Type Healthy Sleepers

The aim of the study was to evaluate the influence of chronotype (morning-type versus evening-type) living in a fixed sleep-wake schedule different from ones preferred sleep schedules on the time course of neurobehavioral performance during controlled extended wakefulness. The authors studied 9 morning-type and 9 evening-type healthy male subjects (21.4 ± 1.9 yrs). Before the experiment, all participants underwent a fixed sleep-wake schedule mimicking a regular working day (bedtime: 23:30 h; wake time: 07:30 h). Then, following two nights in the laboratory, both chronotypes underwent a 36-h constant routine, performing a cognitive test of sustained attention every hour. Core body temperature, salivary melatonin secretion, objective alertness (maintenance of wakefulness test), and subjective sleepiness (visual analog scale) were also assessed. Evening-types expressed a higher level of subjective sleepiness than morning types, whereas their objective levels of alertness were not different. Cognitive performance in the lapse domain remained stable during the normal waking day and then declined during the biological night, with a similar time course for both chronotypes. Evening types maintained optimal alertness (i.e., 10% fastest reaction time) throughout the night, whereas morning types did not. For both chronotypes, the circadian performance profile was correlated with the circadian subjective somnolence profile and was slightly phase-delayed with melatonin secretion. Circadian performance was less correlated with circadian core body temperature. Lapse domain was phase-delayed with body temperature (2–4 h), whereas optimal alertness was slightly phase-delayed with body temperature (1 h). These results indicate evening types living in a fixed sleep-wake schedule mimicking a regular working day (different from their preferred sleep schedules) express higher subjective sleepiness but can maintain the same level of objective alertness during a normal waking day as morning types. Furthermore, evening types were found to maintain optimal alertness throughout their nighttime, whereas morning types could not. The authors suggest that evening-type subjects have a higher voluntary engagement of wake-maintenance mechanisms during extended wakefulness due to adaptation of their sleep-wake schedule to social constraints. (Author correspondence: jack.taillard@gmail.com)

Hypobaric Impact on Clinical Tolerance and 24-h Patterns in Iron Metabolism Markers and Plasma Proteins in Men

Long-distance flights can cause a number of clinical problems due to mild hypoxia resulting from cabin pressurization. Using a chronobiological approach, the aim of this work was to assess the clinical tolerance and biological impact of daytime exposure to hypobaric hypoxia on markers of iron metabolism and plasma proteins. Fourteen healthy, male volunteers, ages 23 to 39 yrs, spent 8.5 h in a hypobaric chamber (from 07:45 to 16:15 h) simulating an altitude of 8000 ft. This was followed by another 8.5-h session 4 wks later simulating conditions at an altitude of 12,000 ft. Biological variables were assayed every 2 h over two 24-h spans (control and hypoxia spans, respectively) per simulated altitude. Whereas most of the subjects tolerated the 8000 ft exposure well, eight subjects (57%) presented clear clinical signs of hypoxic intolerance at 12,000 ft. The 24-h blood iron profile showed a biphasic pattern at both altitude simulations, with a significant (∼40%) increase during hypoxia, followed by a (∼25%) decrease during the first hours of recovery. The iron circadian rhythm showed a significant phase delay during the hypoxic exposure at 8000 ft vs. reference. Mean 24-h ferritin levels decreased at both altitudes, but mainly during the nighttime after the 12,000 ft exposure in accordance with Cosinor analysis. The transferrin and total plasma proteins 24-h profiles did not show significant change. Moreover, significant differences, mainly in iron, ferritin, and transferrin, were found at 12,000 ft according to the clinical tolerance to hypoxia, and significant correlations were found between the mid-range crossing times, i.e., here half-descent times (d-T50), for ferritin and total plasma proteins and the reported level of clinical discomfort under hypoxia. This study shows that an 8.5-h exposure to mild hypoxia is able to alter very quickly the 24-h pattern of iron and ferritin. These alterations seem to depend, at least in part, on the clinical tolerance to hypoxia and may help explain the interindividual differences observed in the tolerance to hypoxia. (Author correspondence: yvan.touitou@chronobiology.fr)