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 percent of inflight nights and ISS crewmembers reported sleep disturbance on 35 percent of inflight nights. 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. Although not included in the daily diary of the previous study due to its insidious nature, low levels of oxygen and high levels of carbon dioxide have been hypothesized to account for sleep disturbances during spaceflight.

METHODOLOGY: Over the past ten years, we objectively assessed, via wrist actigraphy and daily logs, 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 ISS (3,248 inflight days). Thus, we have a database of over 4,000 sleep episodes, which provides a unique opportunity to objectively analyze other environmental factors that may influence sleep during spaceflight. Our research team included NASA investigators and operational personnel who have collected time-stamped environmental data during spaceflight (e.g., noise levels, oxygen and carbon dioxide levels). We statistically evaluated the association among objective and subjective measures of sleep quantity and quality with varying levels of these environmental factors.

RESULTS: None of the sleep variables showed any significant difference between the 14.7 psia and 10.2 psia conditions. There was a significant increase (22 minutes) in total sleep time (TST) when the mean ppCO2 was = 4 mmHg (t=2.62, p=0.01). When controlling for age, gender, and the reported use of sleep-promoting medications, one mmHg increase in the mean partial pressure of oxygen was associated with an increase of 58.8 minutes of TST (p<0.001), a 4.3% increase in sleep efficiency (SE) (p=0.01), an increase 62.1 minutes in somatic symptom disorder (SSD) (p=0.0004) and a 15.3 unit increase in sleep quality (SQ) (p=0.0008). One mmHg increase in the mean ppCO2 was associated with a decrease of 8.8 minutes of TST (p<0.001) and a decrease of 7.4 minutes in SSD (p=0.009). There were no personal acoustic dosimetry recordings at or above 80dBA during actigraphy-defined main sleep episodes; 94% of dosimetry recorded during main sleep episodes were less than 60dBA.

CONCLUSIONS: Environmental factors, such as hypoxia and hypercapnia impact sleep during spaceflight. The collection of environmental data should continue with coordination between the life science and environmental teams so that the data that is collected will have the necessary detail to be usable by both groups. This coordinated research approach could have a substantial impact on countermeasures, interventions and/or policies affecting spaceflight crewmembers in an effort to improve their health, performance, and safety.

The LSDA reviewed the consents given by all the crewmembers. The data from crewmembers who chose free use of any of their data or free use of the sleep data was released to us. We learned that repository consent forms do not cover individual acoustic monitoring exposure data. Thus, LSDA had to re-consent all crewmembers with overlapping sleep data in order for us to be able to use those data in secondary analyses. Data with appropriate consent was released to investigators.

The multiple databases were aligned by date and time so that comparisons between sleep and environmental factors could be analyzed. Statistical analysis was performed by the statistician at Brigham and Women's Hospital. Following the submission of this final report, a presentation will be made to NASA co-investigators and National Space Biomedical Research Institute (NSBRI) personnel and a manuscript may be submitted to a scientific journal for publication.

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 percent of inflight nights and ISS crewmembers reported sleep disturbance on 35 percent of inflight nights.

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. 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. Uncomfortable temperatures (too hot or too cold) were also attributed to disturbed sleep more than 20 percent of the time. Although not included in the daily diary of the previous study due to its insidious nature, low levels of oxygen and high levels of carbon dioxide have been hypothesized to account for sleep disturbances during spaceflight.

We propose to incorporate the existing extensive sleep database to search for associations between environmental factors that NASA routinely records (i.e., hypoxia, noise, hypercapnia) and sleep. Over the past ten years, we objectively assessed, via wrist actigraphy and daily logs, 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). Thus, we have a database of over 4,000 sleep episodes which provides a unique opportunity to objectively analyze other environmental factors that may influence sleep during spaceflight.

We plan to team with other NASA investigators or operational personnel who have collected time-stamped environmental data during spaceflight (e.g., noise levels, oxygen and carbon dioxide levels). We will statistically evaluate the association among objective and subjective measures of sleep quantity and quality with varying levels of these environmental factors.

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.