As you may already know, I love analysing parts of my own life, particularly my sleep (See post about my Jawbone). Let me just prove to you how much of a nerd I am about this. I have compared a week of my sleep, recorded in a ‘sleep diary’ in late March (so, over my birthday)…to the sleep of astronauts and cosmonauts in space. Sleep in Space.
*Small disclaimer: I’ve never been to space
This is stemmed mainly from an old assignment that I’ve now got carried away with and I’ve amended it slightly to be a little easier on the eye, this post is proper nerdy, it’s like a full on essay. I dare you to read it, though, as it’s very very interesting, especially how the different environment in space can effect our sleep! If you would like the references from the full paper to read yourself, then just let me know @kathyathy.
Sleep in Space
Studies on sleep in space are often case studies, self-reported and anecdotal, which are not sufficient measurements to gain statistical significance
(for that, we would need a large sample and operational measures). Small collections of small, objective studies remain consistent though, as
manned spacecraft provide research-heavy environments on strict timescales and use scientific instruments to measure sleep including Electroencephalography (EEG) and Polysomnography (PSG) to ensure scientific accuracy.
Astronauts and Cosmonauts may not be considered the same as normal people due to intense physical and psychological training; they are a different age-range to me, with an average age of 40-50 years. My diary is also not a typical week of sleep, and it was over a birthday weekend (heavy drinking, but I’m allowed – Astronauts may not be!), which may have significantly affected night-to-night variability and quality of sleep, and may in turn may pose an effect on daytime drowsiness and productivity.
Many manned space stations run on Universal Time (UTC), a continuation of Greenwich Mean Time (GMT). Optimal performance is gained if sleep routines are kept constant with space crews’ terrestrial (meaning, on earth – think E.T.) circadian rhythms of 24 – 25.5 hours. Circadian rhythms (our natural ‘body clock’) are resilient enough to function in microgravity and other pressures of orbiting the earth, however sleep schedules may often be shifted to suit the demands of the space mission. When given a free-running schedule, astronauts wish to work earlier in the day, similarly to myself (although I think this has changed since starting the MSc), and suffer decreases in workload and efficiency, which may be compared to more lenient routines on-ground, and I’m sure we can all relate to that!
The opportunity for at least 8 hours of rest-time a night is strictly enforced by NASA; yet space crews often voluntarily reduce this time, resulting in an average Total Sleep Time of 6 hours, which do not significantly differ from pre-flight 6.9 hours average a night. Wake After Sleep Onset scores, meaning the time you had awake after falling asleep for the first time, (WASO) scores increased for space crews when they start their mission in space (0.99 hours in-flight vs 0.77 hours pre-flight) but WASO reduced over time after adapting to the new environment. My WASO score of 0.11 hours, over 0.3 Number of Awakenings over the course of a week (0.42 hours over the two nights that I did) is lower than space crew, however both astronauts and myself present typically uninterrupted sleep.
In day three of my diary, Total Sleep Time was reduced by 1 hour from the advance in time to British Summer Time (BST) resulting in a sudden, but quickly recovered, phase-shift (Total Sleep Time average, 6.58hrs); this effect may also be present for space stations running on UTC-5, for the Kennedy Space Center and UTC-6, for the Johnson Space Center. Time cues such as mealtimes and strict allowances for rest time leads to internal synchronisation after just a few days in space, and similar cues may have the same effect on-ground.
My Time In Bed, the whole time I’m in bed, whether awake or not, (average 8.5 hours) may be a contributing factor to low sleep efficiency (78%) causing daytime drowsiness and low productivity possibly caused by not engaging in bed restriction, limiting myself to time in bed. Sleep cabins in space are microenvironments that omit light which may have a better effect compared to our curtains on-ground, and sleep cabins are only big enough to fit a sleeping bag on restraints, causing cabins to be more likely associated with sleep.
Night-to-night variability on long-duration space flights is low and sleep is considered ‘normal’ and monophasic after the crew have adapted to the new environment. The first and last few nights of sleep on a space mission show greater disturbances and greater need for hypnotics due to a number of possible psychological and physical factors. Emotional factors, homesickness and stress due to workload may contribute to low quality of sleep in both me and astronauts. Many astronauts present sleep disturbances and require the consumption of barbiturates to aid sleep and d-amphetamines to stay awake for fulfilling missions. No drugs aid my sleep or help me stay awake, however the effect of caffeine on my sleep may need to be considered in order to compare to stimulants consumed in space.
Space ergonomics, such as noise and temperature are environmental factors that affect sleep in space, which often resume to normality once astronauts have acclimatised. The effects of microgravity and light-dark alternation on human biological mechanisms are less known (meaning much more interesting!) with light being reported as the most powerful zeitgerber (environmental cue to keep us on the 24 ‘clock’) in space. Space shuttles and stations orbit the earth every 90-120 minutes depending on altitude, which result in light-dark alternation not fitting to a 24-hour timescale. Light-dark cycles can therefore last 80-140 minutes, with 30%-40% darkness, and light may be stronger and have a bigger effect on melatonin above the earth’s atmosphere than below.
Some environmental factors may positively affect sleep quality in space, such as microgravity reducing backaches and tension by relieving pressure and muscle modification. Temperature in space stations is difficult to control, yet often optimal for aiding sleep onset (helping falling asleep), although may also contribute to daytime drowsiness. Re-adaptation to gravity post-flight poses a bigger threat to sleep than effects of sleep ergonomics in-flight.
Watch Helen Sharman (the first Brit in Space), Michael Barratt, Daniel Tani and Jean-Francois Clervoy talk about weightlessness, space walks, and coming home. They talk about sleep in space at around 2:40.
Differences in sleep architecture (the ‘levels’ of sleep – like light sleep and deep sleep) affect sleep more than space ergonomics. Sleep in space is shorter and shallower than on-ground, with a decrease in delta wave and REM (deep sleep) stages. Circadian rhythms are lower in amplitude, resulting in being more phase-liable and malleable to change using light or “artificial darkness” in the microenvironments of sleep cabins than on-ground, meaning it can be easier to change an astronaut’s body clock by artificially changing the environment. A decrease of slow wave sleep (SWS) in space over a long period of time may accumulate a sleep debt and sleep-loss, which will be responsible for detrimental effects on productivity, efficiency and health, as its really important to get your restorative (deep) sleep! As might be expected, Total Sleep Time one week post-flight considerably increased for astronauts to an average 8.5 hours, this effect may be greater for people in my age bracket if under the same conditions, as Slow Wave Sleep is more essential in younger subjects.