Synchronized drowsiness monitoring and simulated driving performance data under 50-hr sleep deprivation: A double-blind placebo-controlled caffeine intervention

This paper presents the 60-s time-resolution segment from our 50-h total sleep deprivation (TSD) dataset (Aidman et al., 2018) [1] that captures minute-by-minute dynamics of driving performance (lane keeping and speed variability) along with objective, oculography-derived drowsiness estimates synchronised to the same 1-min driving epochs. Eleven participants (5 females, aged 18–28) were randomised into caffeine (administered in four 200 mg doses via chewing gum in the early morning hours) or placebo groups. Every three hours they performed a 40 min simulated drive in a medium fidelity driving simulator, while their drowsiness was continuously measured with a spectacle frame-mounted infra-red alertness monitoring system. The dataset covers 15 driving periods of 40 min each, and thus contains over 600 data points of paired data per participant. The 1-min time resolution enables detailed time-series analyses of both time-since-wake and time-on-task performance dynamics and associated drowsiness levels. It also enables direct examination of the relationships between drowsiness and task performance measures. The question of how these relationships might change under various intervention conditions (caffeine in our case) seems worth further investigation.

Improvement in hypoxemia at 4600 meters of simulated altitude with carbohydrate ingestion

BACKGROUND

Carbohydrate ingestion increases the relative production of carbon dioxide which results in an increase in ventilation in normal individuals. An increase in ventilation at altitude can result in improvement of altitude-induced hypoxemia.

HYPOTHESIS

Carbohydrate ingestion will increase the arterial blood oxygen tension and oxyhemoglobin saturation during acute high altitude simulation.

METHODS

There were 15 healthy volunteers, aged 18-33 yr, who were given a 4 kcal x kg(-1) oral carbohydrate beverage administered 2.5 h into an exposure to 15,000 ft (4600 m) of simulated altitude (5.5 h after the last meal). Altitude was simulated by having subjects breath a 12% oxygen/balance nitrogen mixture while remaining at sea level. Arterial blood gas samples were drawn at baseline and at regular intervals up to 210 min after carbohydrate ingestion. Subjects were evaluated for AMS by use of the Environmental Symptoms Questionnaire (ESQ) and a weighted average of cerebral symptom score (AMS-C).

RESULTS

Baseline PaO2 increased significantly (p < 0.01) from 43.0 +/- 3.0 mmHg at 4600 m before carbohydrate ingestion to 46.8 +/- 6.2 mmHg at 60 min after carbohydrate ingestion. Arterial oxygen saturation rose significantly (p < 0.01) from a baseline of 79.5% +/- 5.1 to 83.8% +/- 6.42 at 60 min.

CONCLUSIONS

Carbohydrate consumption significantly increased oxygen tension and oxyhemoglobin saturation in arterial blood of normal subjects during simulated altitude. Effects reached statistical significance across all subjects at 60 min. There was no significant difference in arterial oxygen levels or arterial oxygen saturation in subjects who developed AMS vs. those who did not develop AMS.

Caffeine reversal of sleep deprivation effects on alertness and mood

This study assessed the ability of high doses of caffeine to reverse changes in alertness and mood produced by prolonged sleep deprivation. Fifty healthy, nonsmoking males between the ages of 18 and 32 served as volunteers. Following 49 h without sleep, caffeine (0, 150, 300, or 600 mg/70 kg, PO) was administered in a double-blind fashion. Measures of alertness were obtained with sleep onset tests, the Stanford Sleepiness Scale (SSS), and Visual Analog Scales (VAS). Sleep deprivation decreased onset to sleep from a rested average of 19.9 min to 7 min. Following the highest dose of caffeine tested, sleep onset averaged just over 10 min; sleep onset for the placebo group averaged 5 min. Scores on the SSS increased from a rested mean of 1.6-4.8 after sleep deprivation. Caffeine reduced this score to near rested values. Caffeine reversed sleep deprivation-induced changes in three subscales of the POMS (vigor, fatigue, and confusion) and produced values close to fully rested conditions on several VAS. Serum caffeine concentrations peaked 90 min after ingestion and remained elevated for 12 h. This study showed that caffeine was able to produce significant alerting and long-lasting beneficial mood effects in individuals deprived of sleep for 48 h.

Effects of simulated high altitude exposure on long-latency event-related brain potentials and performance

The N100, P200, N200 and P300 components of the auditory event-related potential were recorded from 10 male subjects at 0900, 1600, and 1830 hours at sea level and again following a rapid ascent to simulated 4300 m altitude. Amplitude and latency of components, ear oximetry, and concurrent performance measures (reaction time and counting errors) were assessed. Amplitude of P300 decreased, while P300 latency and reaction time increased, following ascent to altitude. However, the time course of altitude effects differed for amplitude versus latency. Components N100, P200, N200, and counting errors were unaffected by altitude. The results indicate that central measures of cognitive capacities are differentially sensitive to high altitude. The time course of altitude effects on P300 amplitude versus P300 latency suggests that the two measures reflect different aspects of a response to hypobaric hypoxia exposure.

Effect of high terrestrial altitude and supplemental oxygen on human performance and mood

Sustained exposure to high terrestrial altitudes is associated with cognitive decrement, mood changes, and acute mountain sickness (AMS). Such impairment in aviators could be a safety hazard. Thirteen male soldiers, ages 19-24, ascended in 10 min from sea level to 4,300 m (simulated), and remained there 2.5 d. Four times per day, subjects completed a test battery consisting of nine cognitive tests, a mood scale, and an AMS questionnaire. During one test session per day, subjects breathed 35% oxygen instead of ambient air. Analysis revealed transient deficits on altitude day 1 for three cognitive tasks. Most tasks displayed a persistent training effect. Sick subjects' moods were more negative and their performance improvement less. On altitude day 1, oxygen administration improved performance on two cognitive tests and one mood subscale. Following rapid ascent to 4,300 m, performance is most affected during the first 8 h. Individuals affected by AMS tend to improve more slowly in performance and have more negative moods than those who feel well.