Medical Insight of Living in Space from Research at the International Space Station
One of the main premises behind building, operating, and conducting research on the incredibly massive and expensive International Space Station was to learn more about how humans, and life in general, respond to long-term living in space. The ISS was built with manned space missions in mind, and the extensive research in astronauts’ health and wellbeing aboard is used to aid in the technical aspects and training of proposed missions like the one to Mars. The following is a report on recent research solely conducted on astronauts aboard the ISS, as it is the most accurate and credible source of insight into the living conditions of humans in future space missions.
Eight Russian astronauts aboard the ISS for six months participated in a study on the effects of long-term microgravity exposure autonomic cardiovascular and respiratory control (Baevsky et al., 2007). Several medical tests, including blood pressure, heart rate, heart rate variability, and respiratory frequency, were conducted before, during, and after the mission. The study concluded that the average heart rates of the astronauts remained relatively constant before and after the mission, while the average respiratory frequency and blood pressure decreased in seven of the eight astronauts during the space mission with a statistical significance (p-value<0.05).
A common complication for ISS astronauts is the susceptibility to eye injury and vision loss because of microgravity’s effect, or lack thereof, on the human eye. A study conducted on seven astronauts aboard the ISS attempted to find out what these effects were, by taking complete eye examinations, including OCT and MRI scans, of the astronauts before and after their missions (Mader et al., 2011). Among the results, five astronauts were diagnosed to have developed disc edema, the swelling of the optic disc, and globe flattening, the distortion of the front of the eye, and six reported decrease in near vision.
The ISS has a 6 to 10-day rotating food menu, consisting of pre-dehydrated, nutrient-packed meals. Eleven astronauts aboard the ISS for six months were the subjects of a study on the metabolic and nutritional effects of long-term reliance on the ISS’s food system and of living in microgravity (Smith et al., 2005). The body weight of the astronauts decreased by 5%, the urinary concentration of 80HdG rose by about 35%, indicating increased DNA damage, the vitamin D status indicator decreases by about 25%, and the general energy intake by calorie was about 80% of the WHO’s recommendation for adults.
Though muscle atrophy in space has counter measures such as exercise and diet, bone loss and damage are much less preventative and more dangerous to one’s long-term health. A study on 23 astronauts aboard the ISS used blood and urine tests taken during the astronauts’ missions to determine the risk of bone loss by excess iron and oxidative damage (Zwart et al., 2013). The study concluded that ferritin, an acute phase protein released in response to inflammation, is a good indicator of bone damage since ferritin concentration in blood was found to have a correlation with superoxide dismutase (oxidative damage), with a correlation coefficient of -0.32. The correlation coefficient between ferratin concentration and the total bone mineral density in the astronauts was -0.47.
Figure 1: Visual representation of the sleep cycles of three astronauts who participated in the study. The x-axis is the standard clock time aboard the ISS in hours, and the y-axis shows the day. The grey bars display the sleep time and the white circles show the simulated minimum body temperature in response to the circadian rhythm.
One of the seemingly less serious problems astronauts aboard the ISS face is irregular sleep cycles, but it is one of the most important for such a high-stakes and focused role. Since the Sun sets around 16 times in the 24-hour day aboard the ISS, astronauts’ circadian cycles are thrown off from humans’ natural tendency to sleep in the dark and wake up in the day. In one study, 21 astronauts aboard the ISS recorded sleep logs and took questionnaires in order to compare their sleep cycles during the mission with the control on Earth (Flynn-Evans et al., 2015). One in five sleep episodes was characterized as circadian misaligned, when the astronauts went to sleep in the brightest time aboard and woke up at the darkest time aboard. During these sleep episodes, the astronauts slept about 1 hour less per night, 24% of astronauts used sleep medication compared to 11% during normal sleep episodes, and use of other medication was 63% compared to 49% during normal sleep episodes. Figure 1 displays data taken from three astronauts, with the sleep cycles in grey and circadian temperature, simulated body temperature responses to circadian rhythms, in white dots.
Works Cited
Baevsky, Roman M., Victor M Baranov, Irina I. Funtova, et al. “Autonomic cardiovascular and respiratory control during prolonged spaceflights aboard the International Space Station.” Journal of Applied Physiology. 103, no. 1 (July, 2007) [Cited 25 October 2016].
Dijk, Dirk J., David F. Neri, James K. Wyatt, et al. “Sleep, performance, circadian rhythms, and light-dark cycles during two space shuttle flights.” American Journal of Physiology. 281, no. 5 (November, 2001) [Cited 25 October 2016].
Mader, Thomas H., Rober C. Gibson, Anastas F. Pass, et al. “Optic Disc Edema, Globe Flattening, Choroidal Folds, and Hyperopic Shifts Observed in Astronauts after Long-duration Space Flight.” Ophthalmology. 118, no. 10 (October, 2011) [Cited 25 October 2016].
Smith, Scott M., Sara R. Zwart, Gladys Block, et al. “The Nutritional Status of Astronauts Is Altered after Long-Term Space Flight Aboard the International Space Station.” The Journal of Nutrition. 135, no. 3 (March, 2005) [Cited 25 October 2016].
Zwart, Sara R., Jennifer LL Morgan, Scott M Smith, et al. “Iron status and its relations with oxidative damage and bone loss during long-duration space flight on the International Space Station.” The American Journal of Clinical Nutrition. 98, no. 1 (July, 2013) [Cited 25 October 2016].
