Environmental Factors Associated with Sleep Deficiency During Spaceflight
Principal Investigator:
Laura K. Barger, Ph.D.
Organization:
Brigham and Women's Hospital
After landing on the moon in 1969, Astronaut Neil Armstrong was reportedly unable to sleep all night and Astronaut Buzz Aldrin managed only “a couple of hours of fitful drowsing” during their 21.6 hours on the moon, reportedly because they could not escape from light and noise in the small cabin of their spacecraft and the spacesuit’s cooling system made it too cold for sleeping.1 Environmental factors continue to impact sleep in the modern era of spaceflight.
During a ten-year study of sleep aboard Shuttle and International Space Station (ISS) missions, crewmembers reported sleep disturbances via a daily log. Shuttle crewmembers reported sleep disturbance on 58% of inflight nights and ISS crewmembers reported sleep disturbance on 35% of inflight nights. This project will leverage this existing sleep database to search for correlations between environmental factors that NASA routinely records (i.e., hypoxia, noise, hypercapnia) and sleep.
NASA Taskbook Entry
The sleep-wake timing of 64 astronauts on 80 Space Shuttle missions, encompassing 26 Space Transportation System flights (1,063 inflight days), and 21 astronauts on the International Space Station (ISS) (3,248 inflight days) was objectively assessed, via wrist actigraphy and daily logs. Astronauts continuously wore a small, light-weight activity- and light-recording device [Actiwatch-L (AWL);MiniMitter/Phillips Respironics, Bend, OR] throughout the spaceflight mission. Sleep duration was estimated in two-minute epochs from actigraphy data using Actiware Software. Astronauts also kept a daily sleep and medication log throughout their spaceflight mission. Subjective measures of sleep recorded in the diary included sleep quality and number of sleep disturbances. This database of over 4,000 sleep episodes provides a unique opportunity to objectively analyze environmental factors that may influence sleep during spaceflight.2 Although crewmembers during that extensive study were asked to subjectively identify the cause of sleep disturbances, the role of objective environmental factors in sleep disturbances has not been previously investigated.
There are numerous stressors that are unique to the spaceflight environment that might account for sleep disturbances and prompt use of sleep-promoting medications. Noise, which can disrupt slow wave and REM sleep, both of which are critical to the restorative function of sleep, remains a major source of sleep disruption in modern spaceflight. Both shuttle and ISS crewmembers attributed 1 in 5 inflight disruptions to noise.1 Operational demands of space missions often result in the continuous noise levels in the range of 56-69 dBA and often higher within habitable areas of the ISS. Dosimetry measurements during ISS Increments 2-14 reveal noise levels during sleep episodes as high as 72 decibels. Researchers conducting laboratory-based studies have reported that noise levels similar to those experienced by astronauts during space missions could lead to sleep disruption and subsequently impaired cognitive functioning.3 Although not included in the daily diary of the previous study due to its insidious nature, hypoxia and high levels of carbon dioxide have been hypothesized to account for sleep disturbances during spaceflight.4 A team of sleep investigators will collaborate with NASA investigators and operational personnel who have collected time-stamped environmental data during spaceflight (e.g., noise levels, oxygen and carbon dioxide levels) to evaluate the correlation among objective and subjective measures of sleep quantity and quality with varying levels of these environmental factors.
The following questions will be specifically addressed:
Is hypoxia associated with increased sleep disturbance and deficiency?
Is increased noise associated with increased sleep disturbance and deficiency?
Is hypercapnia associated with increased sleep disturbance and deficiency?
The association among sleep disturbance and deficiency and hypoxia, noise and hypercapnia will be statistically analyzed. Potential confounders such as age (continuous variable), gender and time of day, circadian phase and medication use will be controlled.
The proposed study will impart knowledge on the impact of environmental factors on sleep during spaceflight. NASA will be able to use the knowledge gained to inform the planning and design of future spacecraft environments to optimize sleep and behavioral health of crewmembers on future exploration class space missions.
References
- National Aeronautics and Space Administration. Wide awake on the sea of tranquility. July 20, 2006. http://www.nasa.gov/exploration/home/19jul_seaoftranquillity.html (accessed April 12, 2013).
- Barger LK, Flynn-Evans EE, Kubey A, Walsh L, Ronda JM, Wang W, Wright KP Jr, Czeisler CA. Prevalence of sleep deficiency and use of hypnotic drugs in astronauts before, during, and after spaceflight: an observational study. Lancet Neurol. 2014 Sep;13(9):904-12.
- Smith, DG, Baranski, JV, Thompson, MM and Abel, SM. The effects of background noise on cognitive performance duringa 70 hour simulation of conditions aboard the International Space Station. Noise & Health, 2003. 6 (21): 3-16.
- Croynin, PD, Watkins, S, and Alexander, DJ. Chronic Exposure to Moderately Elevated CO2 during Long-Duration Space Flight. NASA/TP-2012-217358. NASA Center for AeroSpace Information Hanover, MD. http://ston.jsc.nasa.gov/collections/TRS/
The proposed research could have significant implications for both sleep disorders medicine and space life sciences. The results of the proposed research could lead to the development of a new treatment regimen for sleep disturbances of various etiologies during space flight, which could enable crew members to avoid the decrements in alertness and performance associated with sleep deprivation. This work could therefore have a profound impact on the health, productivity and safety not only of astronauts during space flight, but also of other groups with a high prevalence of insomnia, such as shift workers and older people.
