Commercial Astronauts by Erik Seedhouse

Author:Erik Seedhouse
Language: eng
Format: epub
ISBN: 9783031556043
Publisher: Springer Nature Switzerland

Fig. 6.12The sliding filament theory. (Credit: David Richfield)

Of course, countermeasures for bone loss and muscle atrophy will comprise only part of the suite of exercise equipment that will be available to commercial astronauts because having strong bones and muscles will only get you so far; astronauts also need to maintain their exercise capacity. One metric for measuring aerobic capacity is maximal oxygen uptake which measures the amount of oxygen utilized by each kilogram of bodyweight per minute of exercise. As a commercial astronaut you will undoubtedly perform preflight, inflight and postflight measures of oxygen uptake and, like all physical fitness metrics, you will undergo an observed decline in your ability to utilize oxygen. Why? Well, first there is the issue of muscle atrophy. Imagine losing 20–25% of your respiratory muscle mass (your intercostal and intracostal muscles). This will make breathing more difficult. And then of course there is the loss of working (skeletal and cardiac) muscle mass. If your muscles—and heart!—are smaller, it stands to reason you will find it more difficult to work out. How much more difficult? Well, compared with pre-flight data, maximal oxygen uptake declines by between 15% and 25%.

So, by now we know astronaut’s bodies suffer in microgravity. Without effective countermeasures, muscles atrophy, bones shed calcium, and astronauts get sick. But that’s not all. Eyesight may also be affected. We’ve known about vision impairment in astronauts for some time, but the problem has only been put under the spotlight recently after some astronauts experienced severe eyesight deficiencies. Thanks to anecdotal reports by astronauts and a comparison of pre- and post-flight ocular measures, microgravity-induced visual acuity impairments have now been recognized as a significant risk (you can read more about this in Springer’s Microgravity and Vision Impairments in Astronauts written by yours truly). And this problem doesn’t affect a minority of crewmembers: retrospective analysis of medical records revealed 29% of 300 Shuttle astronauts and 60% of space station astronauts have suffered some form of visual degradation. That’s a serious problem for an agency planning to send astronauts back to the Moon and eventually Mars. The problem has its own acronym—this is NASA after all—and is referred to as the visual impairment/ intracranial pressure (VIIP) syndrome. Even though VIIP has only recently been identified, there has been significant research performed, so scientists are beginning to better understand the syndrome. The data shows that astronauts who suffer VIIP related symptoms experience varying degrees of visual performance decrements. Some suffer cotton-wool spot formation while others may present with edema of the optic disc. Other astronauts may suffer flattening of the posterior globe while some may present with distension of the optic nerve sheath. In short, there is a profusion of signs and symptoms but the reason for the vision impairment still has researchers flummoxed. One theory suggests the changes in ocular structure and impairment to the optic nerve is caused by the cephalothoracic fluid shift astronauts experience while on board the ISS. It is theorized some astronauts are more sensitive to fluid shift due to genetic and anatomical factors.

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