Space Walks

The space shuttle Endeavour landed yesterday at Kennedy Space Center in Florida.

Endeavour's two-week assignment to the International Space Station was shortened for safety arrangements concerning Hurricane Dean.


The Endeavour name uses British spelling because it was named for the HMB Endeavour, a sailing ship commanded by 18th century explorer James Cook. Before launching the space shuttle Endeavour, NASA hung a humorous, quickly replaced "GO Endeavor" banner. The formal name is STS - Space Transportation System. This mission was STS-118.


During STS-118, crewmembers went outside the vehicle for assorted tasks. Going out is called extravehicular activity (EVA). Crew going on EVA wear pressurized suits to protect against radiation, space debris, temperature extremes, and low air pressure. The suits aren't just called suits, they are Extravehicular Mobility Units (EMUs). EVAs get interesting because EMUs are pressurized higher than the near vacuum of space, since space doesn't support human life, but not as much as inside the shuttle. The lower air pressure inside EMUs increases risk for various problems like gas embolism, but chiefly, decompression sickness, also called the bends.

Air pressure around us keeps nitrogen gas dissolved all over in our body all the time. When you go up a mountain, in a high airflight, or on an EVA, there is less surrounding pressure. Nitrogen becomes undissolved. If you reduce pressure slowly enough, nitrogen comes out peaceably and you can breathe it out. If you come up from a scuba dive or jump out for your EVA too fast, nitrogen offgases too fast, making bubbles, which are believed to be the basis of decompression sickness. Beside the role of exercise in countermeasures for space health and after returning, exercise is one of several factors affecting risk of decompression sickness. The post Exercise and Fitness in Decompression Sickness Risk explains.

If you could start an EVA with less nitrogen in your body, you could reduce your risk of decompression sickness. Crew preparing for an EVA do lengthy de-nitrogenation procedures. They breathe oxygen instead of air, and do physical exercise to "wash-out" nitrogen in several stages taking many hours. One goal of aviation scientists is to develop faster protocols for denitrogenation without increasing risk of decompression sickness during EVA.

American and Russian space programs use different denitrogenation protocols and different EVA suits. Russians use EMUs with higher suit pressure. The American suit design uses lower pressure, making it more flexible and maneuverable. The lower pressure suit is considered riskier for decompression sickness, and needs longer prebreathing and denitrogenation exercise. The Russian suit, higher pressure inside, is stiffer, needing more muscle to move. My Russian scientist friends say it is like the AK-47 - tough but good. My American scientist colleagues state that the Russian egress suit is a bull, lacking dexterity. My Russians reply they don't need it, as their vehicles, suits (and cosmonauts) are built strong and austerely, not needing fussy fine-tuning. Da.

My crew surgeon friends from both agencies are all submerged in triplicate paper forms for permissions to send me mission stories and photos to post for you. Nice that everyone can feel universally understood.

Labels: aerospace, altitude, scuba

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Altitude Sickness, Viagra, and Bubbles on Flights

The previous post Altitude Sickness During Flights told how certain symptoms occurring during air travel are from exposure to altitude.

If a craft were not pressurized, cabin pressure would be equivalent to the air pressure outside the aircraft at whatever altitude. At high altitude, there would not be enough air pressure inside for crew to be functional enough to fly. This was one of my areas of study with the Navy. Crew in unpressurized craft wear oxygen-delivery equipment.

Passenger planes are pressurized. The inside is kept at a higher pressure (lower equivalent altitude) than flight altitude (the air outside the plane). The pressure is still not as much as at sea level. Keeping that much interior pressure would create huge fuel costs and extreme metal fatigue on the craft. Regular passenger aircraft keep interior pressure equivalent to mild altitude exposure.

In the last few years, Viagra (sildenafil citrate) has been tested by various groups, including the military, as intervention against altitude sickness. Recently it was also found that the drug reduced symptoms, thought to be jet lag, after flights. My guess is that it was effective for symptoms from flights because of the same properties that may help reduce symptoms, in some, of altitude sickness.

Another component that I discovered many years ago in my work in altitude sickness, was a bubble component - an altogether new dimension to the altitude sickness puzzle. Decompression sickness bubbles can form in the body when coming up after a scuba dive. I found the same kind of bubbles can form in your body when going to elevations encountered in aircraft and mountain travel, with no prior scuba diving. More of this in future posts. Decompression sickness is also an issue when going into space during extra-vehicular activities. Click Space Walks.

Altitude sickness in flight is different from (or in addition to) the motion sickness of flight motion, or being stiff after not moving enough during long flights. The post Exercise and Stretch for Long Travel Sitting covers some exercises and stretches to relieve those problems.

Labels: aerospace, altitude, drugs, injury, scuba

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Altitude Sickness on Flights

It has made recent news that certain symptoms during air travel are due to altitude sickness. This seems simple enough. Air pressure inside common passenger aircraft is equivalent to mild altitude exposure.

People who get symptoms when going to the mountains may get the same headache, tiredness, achyness, and other symptoms of altitude in flight. Drinking alcohol adds to symptoms. Severity of symptoms depends on several things, mainly how high the altitude, and how fast you reach it.

Cabin pressure varies with cruising altitude and type of aircraft. During a flight, the inside of a large commercial passenger air flights may range between 5000 to 9000 feet (~1525-2743 meters), occasionally higher or lower. Small lower planes flying may be able to maintain pressures closer to (or equal to) ground pressures.

How fast aircraft reach these altitudes depends on the flight path, final cruising altitude, type of aircraft, and other factors. Some of my commercial pilot friends say they will pressurize the cabin far more gradually when they see babies onboard, so that they (the babies) cry less as pressure changes around their ears. Pressure change on the ears is not altitude sickness, just simple air volume change. Earplugs do not prevent this problem, and can make it worse in some situations. Future posts can cover why.

Susceptibility to altitude sickness does not seem to be affected by better or lesser physical conditioning, or any kind of fitness or physical training. It is still a hugely interesting topic to understanding how the body reacts to and works at altitude, why certain interventions work or don't, and how soon you can fly after going scuba diving - important to risk of decompression sickness.

Reader Bill, athlete and pilot, writes, "Regulations require no more than a 10,000 foot cabin altitude (3048m) be maintained for commercial passenger flights. Anyone not acclimatized to altitudes between 7 to 10 thousand feet (~2-3 thousand meters) will feel some symptoms of a mild hypoxia, surely after several hours or/and a couple stiff drinks."

The next post tells more about altitude sickness on flights and more interesting issues and a few proposed cures.

Labels: altitude, injury

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