Date: July 31, 2010
Title: Space Medicine
Podcaster: Mick Vagg
Description: A medical themed podcast, exploring the unique challenges to medical science in keeping astronauts, cosmonauts and all other space travellers well enough to return in good shape from trips to space.
Bio: Dr. Michael Vagg is a physician specializing in Rehabilitation Medicine and Pain Management. He lives in Torquay, in the Surfcoast region of Australia. One day he hopes to be able to remember more than five constellations and own a telescope bigger than Galileo’s.
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Transcript of 365 Days of Astronomy July 31 – Space Medicine
Dr Mick Vagg
Greetings again from the Surfcoast in Southern Australia. In today’s podcast we return to a medical theme, exploring the unique challenges to medical science in keeping astronauts, cosmonauts and all other space travellers well enough to return in good shape from trips to space. During my stint some years ago with the Australian Air Force as a Medical Officer I was able to spend some time studying aerospace medicine but the stresses of subspace flight on the body are one thing, and the far more extreme environment of space is another again.
Let’s look at how the space environment is different from earth. Firstly and perhaps most obviously, there is no atmosphere in space. This means no oxygen to breathe and no pressure from the outside of the body pressing inwards. As one ascends beyond around 20 000 feet the amount of oxygen in the air becomes so low that without supplemental oxygen one loses consciousness within a minute or two. Having ascended to just such a height and taken my oxygen mask off, I can certainly vouch for the fact that without the instructor to prompt me to put it back on after about 90 seconds I could not have done it, my thinking was that scrambled. I tried to write my name, which I can barely remember doing, and it was just scrawl after the first letter.
The atmosphere also contains nitrogen, and the presence of nitrogen dissolved in the tissues of the body leads to another severe hazard of low atmospheric pressure – the bends. This more technically known as Decompression Sickness or DCS. DCS occurs when the pressure of nitrogen outside the tissues is much lower than that of the dissolved nitrogen in the body. The tissue nitrogen tries to equilibrate with the ambient pressure and this leads to the generation of tiny and sometimes not-so-tiny nitrogen bubbles. The bubbles begin most often in the joints, leading to excruciating joint pains, hence the name ‘the bends’. More seriously, DCS microbubbles can lead to obstruction of the blood flow in tiny blood vessels throughout the body, especially in the brain which is so critically dependent on a vigorous blood supply. Thus DCS if severe and not rapidly treated can lead to permanent tissue damage of end-organs including brain, kidneys, lungs and heart. The main risk to space travellers of DCS occurs during spacewalks, or EVAs. The NASA Space Medicine program has established a procedure called ‘nitrogen washout’ whereby the astronaut who will be performing the EVA breathes 100% oxygen for an hour or so prior to exiting the craft which displaces the nitrogen out of the tissues and replaces it with oxygen. If not carefully and slowly done this can lead to oxygen toxicity, but since the protocol was introduced, NASA reports there have been no cases of oxygen toxicity and no astronauts have been bent following EVAs.
Another obvious problem in space is the lack of ambient pressure. In the second Voskhod mission, flown by the USSR in 1965. The goal of the mission was to beat the Americans to be the first to perform an EVA. There had been several failures during testing of the airlocks on the spacecraft, and not much thought had been given to the actual effects of depressurization on the cosmonauts’ suits. Aleksei Leonov spent 12 minutes outside the capsule before he realized that the suit had expanded so much in the low pressure environment that he couldn’t get back inside the entry bay of his craft. At extraordinary risk he had to carefully let some of the pressure out of his suit. If he did it too quickly he would pass out from the sudden drop in his blood pressure, and die in space. He had to enter the airlock head first instead of feet first as it was designed, and from the time he realized his peril to time he repressurized it took 11 further minutes. By the time he was back inside, his heart was beating at over 140 a minute, compared with his resting rate of less than 60, his breathing rate was 40 a minute instead of 16 and his body temperature was 38 degrees (100 F), and he had barely survived his brush with the ultra-low pressures of space.
Unfortunately for the crew of Voskhod 2 their problems with the harsh environment of space flight did not end there. On the descent their automatic retro rockets failed to fire and the instrument capsule failed to properly separate from the descent module. The end result of this was a steep descent and an encounter with severe G forces. A force on the body equal to the force of the earth’s gravity at sea level is known as 1 G. One of the major stresses of the flight environment is exposure of the body to acceleration forces of more than 1 G. Most average people will black out at 4-5 G as the blood in their arteries fails to make it to the brain, which then loses function. A well-trained fighter pilot using a special breathing maneuvre to keep the blood pressure in the chest and head high can withstand 6-8 G for more than a minute before blacking out. I managed to survive 40 seconds of 4.5 G in an aerobatic aircraft but I was beginning to weaken. I could not lift my hands off my lap despite trying to get my camera into position for a photo ! Leonov, and his crewmate Pavel Belyayev suffered forces that reached 10G during the descent, which caused several blood vessels in their eyes to rupture. Fortunately their sight was preserved and they landed safely.
Perhaps the most obvious stress of the space environment is the microgravity environment. As the early space missions went for longer and longer the physiological changes caused by microgravity needed to be better understood. ‘Space Sickness’ which was the urgent need to throw up with very little warning was felt to be one of the more benign manifestations of the body trying to adjust to microgravity. Over time the body tends to reduce the blood volume and begin reducing the amount of calcium in the bones. Countermeasures to prevent this include exercising in artificial gravity while in orbit, taking medications to expand the blood volume fairly quickly after return to earth and more recently taking medication to reduce the bone loss and accelerate the reaccumulation of lost bone mass. Before the current generation of bone-building medication was available it took up to 3 years to regain the bone lost in a 3-4 month space flight. Muscles which have become wasted in space need time and effort to be rebuilt. The finely tuned balance mechanisms of the middle and inner ear often take some time to adapt in microgravity with feelings of disequilibrium and poor balance in space, and then again on return to earth. Related to this is a sensation of spatial disorientation, which plagued the early Russian missions. On Voskhod 1 two of the three cosmonauts became spatially disoriented at the same time during the first three hours of the flight.
An interesting and slightly unexpected finding of microgravity research was that time in space reduces the ability of the immune system to fight off infections. The T cells which are a major immune link in the immune response become much less effective after even a relatively brief period of microgravity. Astronauts have a period of quarantine upon return to reduce the chance of opportunistic infection.
The final problem with lack of an atmosphere is the exposure to radiation from the sun and from deep space. We don’t really think much about the extent to which our magnetosphere and atmosphere protect us from radiation, but in space it is a major issue, and is probably the single biggest obstacle from a medical point of view to us going beyond the moon. The cosmonaut Valentin Lebedev set a record for time in orbit in 1982 of 211 days on Salyut 7 and went on to lose his eyesight at the age of 66 in both eyes due to cataracts, most likely due to radiation exposure.
Some spinoffs of space medicine research have included advances in kidney dialysis and medical imaging technology. Telemetry, or remote monitoring of medical information such as heart rate, blood oxygen levels, and blood pressure that was developed for NASA has been successfully used by the military and civilian emergency services. These systems allow the doctors at the receiving facility to monitor incoming casualties and give advice to the paramedics during transport. Pressure relief systems for wheelchair users of those with poor skin integrity have been developed from NASA materials used to help the astronauts sleep comfortably in low gravity. So the benefits of aerospace medicine are available to everyone, even those who haven’t been into orbit and back.
Clear skies to you all.
End of podcast:
365 Days of Astronomy
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