Recent data indicate that some crewmembers take medications twice in one night. The sleep medications used in space flight are FDA approved for sleep periods of eight hours or more, but they have not been studied for their effects on waking cognitive functions during an alarm-based awakening from sleep (under eight hours) that has occurred in space flight numerous times. There is a need to identify the cognitive effects of sleep medications during such premature awakenings, and to identify the sleep medications and dosages that produce the fewest cognitive effects and adverse reactions in individual astronauts. Consequently, the study aimed to characterize the effects of the most commonly used sleep medications and dosages on performance after an unplanned awakening, while providing the foundation for future development of individualized protocols for sleep medication use during training and on-orbit.
The pilot study was successfully tested on seven subjects from March through June, 2009. The pilot study results supported the scientific feasibility of conducting a randomized, blinded, placebo controlled study of sleep medication effects on simulated alarm-based awakenings. Preliminary analysis from the pilot study indicated differences in performance upon abrupt awakening between the sleep medication and placebo conditions. Thus, the pilot data also support the likelihood of new scientific and clinical insights from the Phase II studies with NASA astronauts.
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In Phase II, two randomized, blinded, placebo-controlled, cross-over trials were conducted. Zolpidem (Ambien) is the most commonly and Zaleplon (Sonata) is the second most commonly used sleep aid medication in space flight. In Phase II, the hypnotic medication and the placebo were indistinguishable by subjects. Experiment 1 involved N=14 subjects randomized to placebo, 10 mg zolpidem, and 10 mg zaleplon in counterbalanced order. Those astronauts who had a previous adverse experience with 10 mg zolpidem were empanelled into Experiment 2, which involved N=20 subjects randomized to placebo, 5 mg zolpidem, and 10 mg zaleplon.
The experiments yielded results that were fully consistent with the intended goals of identifying the effects on performance and neurobehavioral functions from abrupt awakening from sleep at a time when commonly used sleep medications (10 mg zaleplon, 5 mg zolpidem, 10 mg zolpidem) are near pharmacokinetic time to maximum effect (Tmax) as well as at terminal awakening in the morning. While Tmax post-awakening performance (i.e., vigilance, cognitive processing speed, working memory, free recall) was affected in nearly all subjects, some individuals demonstrated minimal to no deficits, while others demonstrated substantial cognitive decrements. This finding highlights the feasibility of utilizing the study paradigm to personalize the sleep mediations and dosages astronauts use in space, and acquaint them with information on how to avoid performance deficits if awakened abruptly from sleep after ingesting a hypnotic. The protocol can also be used to evaluate the residual carryover effects of other sleep medications and sedating agents.
Descending subtraction task (DST) number correct
Descending subtraction task (DST) number of errors
Mental fatigue ratings, mean
Physical exhaustion ratings, mean
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Psychomotor vigilance test false starts
Psychomotor vigilance test fastest reaction time
Psychomotor vigilance test mean reaction time
Psychomotor vigilance test performance lapses
Psychomotor vigilance test response speed
Psychomotor vigilance test total errors
Sleepiness ratings, mean
Stress ratings, mean
Time to respond to alarm
Tiredness ratings, mean
Words recalled correctly
Words recalled incorrectly
Crew health and performance is critical to successful human exploration beyond low Earth orbit.
The Human Research Program (HRP) investigates and mitigates the highest risks to human health
and performance, providing essential countermeasures and technologies for human space exploration.
Risks include physiological and performance effects from hazards such as radiation, altered gravity,
and hostile environments, as well as unique challenges in medical support, human factors,
and behavioral health support. The HRP utilizes an Integrated Research Plan (IRP) to identify
the approach and research activities planned to address these risks, which are assigned to specific
Elements within the program. The Human Research Roadmap is the web-based tool for communicating the IRP content.
The Human Research Roadmap is located at: https://humanresearchroadmap.nasa.gov/
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for information of how this experiment is contributing to the HRP's path for risk reduction.