Mars

The Challenge of Weightlessness by Duane Graveline, MD and Fred Kelly, MD

Forty years ago, we began bed rest and water immersion studies to help delineate the consequences of prolonged exposure to weightlessness. Muscle strength loss, bony demineralization, diminished ability of the circulatory system to compensate for the erect posture, decreased total body water, circulating blood volume and red cell mass all were predicted on the basis of such studies.

All have been confirmed as operational experience has been gained. We also have made considerable progress towards the development of effective countermeasures to protect the returning astronauts and cosmonauts. Their importance can best be summarized in a recent statement by the Director of the Institute for Biomedical Programs in Moscow, Dr. Anatoly Grigoriev, "Without countermeasures, long duration flights are impossible.

Cosmonauts now have been exposed to prolonged weightlessness for periods approximating one year with safe return but this has come with considerable cost and should offer no grounds for complacency. The weightlessness issue is far from resolved. Now, as we are considering a possible Mars mission in the not too distant future, the operational requirements for this problem loom just as challengingly as they did in the sixties. Doctor Grigoriev adds, "Actually, we do not have medical restrictions on the duration of spaceflight.

We find no correlation between flight duration and changes to the cosmonaut but rather between countermeasures used and changes to the cosmonaut." Furhermore, he stated, they do not try to prevent completely all the changes which occur because too much time would be required. He estimated in excess of three hours each day would be required for self maintenance to achieve this. Even the customary two hours per day their cosmonauts prefer is expensive and excessively consuming of operational time.

The Russian program, according to Doctor Grigoriev, has created a safe and reliable system of medical support, combining preflight selection, in-flight monitoring, countermeasures and post flight support. None can doubt that their system has worked for MIR. Now, we ask ourselves, can this same system be used for Mars mission support? I think the answer is yes, but with very important qualifications.

THE CHALLENGE
Our first challenge will come with descent to the surface of Mars for once again after a prolonged absence of weight our Martian explorers will feel the pull of gravity. Yes, you say, but it is only a little better than one third Earth gravity - a piece of cake compared with Earth return. This is true but remember, our post flight recovery team no longer is available to meet them with stretchers, wheelchairs, recliners and intravenous setups.

With our present knowledge can you guarantee our explorers will be able to handle operational demands and unforeseen stresses immediately upon descent? Remember, their lives depend upon your judgment. They have to walk and move about. They have to be fully functional. If we have a good enough system of medical support, our in-flight monitoring of muscle strength and circulatory responsiveness should tell us how fit our explorers will be on Martian landings and what, if any, special support might be required - a chap type G-suit, perhaps, or a temporary recliner or fluids. If our program of in-flight countermeasures has been sufficient perhaps nothing will be required but at this point in time we cannot make that prediction. Much remains to be done by our researchers.

SOYUZ 11
Perhaps there is something to be learned from the Soyuz 11 disaster that is relevant to this subject. Cosmonauts Dobrovolsky, Volkov and Patsayev were killed on 30 June, 1971, when air in their Soyuz 11 spacecraft rushed out through an exhaust valve that was accidentally triggered open. Two of the cosmonauts unhooked their seat belts and tried to rise from their couches to close the valve, located above the head of the cosmonaut in the center seat.

Within only a few seconds the cabin pressure fell too low to sustain consciousness. In less than a minute no cabin air remained. In the Air Force we always said the time of useful consciousness after a rapid decompression is thirteen seconds, the time required for blood to pass from the lungs to the brain. Russian doctors said the cosmonauts had no hope of survival. The recovery team found the cosmonauts dead in their seats, one having sustained a deep facial bruise.

The crew of Soyuz 11 had spent 24 days in space and with the relatively small space available had little or no access to an effective countermeasures program such as bicycle ergometer or treadmill. The fact that they tried to close the valve indicates to me that this procedure was technically possible but they were unable to do it.

I suspect muscular deconditioning to be a major contributory factor in this accident. It is likely that these men were unable to rise from their seats with the strength and agility required to close the valve above their heads, They were too weak! A task they might have been able to perform with ease 24 days ago now was impossible! They could only fall back and watch their lives hissing into space - the first deaths where deconditioning might well have been a contributing factor.

INFLIGHT MONITORING AND COUNTERMEASURES
The challenge we face, then, is to design a system of medical support for a Mars mission. Taking the lead from Doctor Grigoriev I should like to direct my attention first to the in-flight monitoring and countermeasures part of the system. I include them together because each is dependent upon the other. If the monitoring reveals that excessive muscle weakness or bony demineralization is occurring then musculoskeletal exercises must be done for longer duration or with greater vigor. And the reverse holds true. If excessive strengthening of muscle groups occurs, reflecting too much time on the exercise device, that self maintenance time should be reduced and directed to operational demands.

Certainly, exercise periods on the treadmill, bicycle ergometer or rowing machine will be mandatory and this, hopefully, will require no more than two hours each day, a figure probably considered barely acceptable by mission control personnel. It is likely that the exercise periods will have to be supplemented by the routine wearing of a device comparable in effectiveness to the Russian, Penguin-3, muscle and bone loading suit. Only by close monitoring of muscle strength and bone densitometry will the final figures for in-flight exercise duration and intensity be derived. Much additional research remains to be done.

Similarly, the lower body negative pressure device which, incidentally, I developed in the early sixties at the AF School of Aerospace Medicine must be administered periodically to determine the ability of each crew member's circulatory system to compensate for hydrostatic pressure effects during the trip to Mars. This ability is dependant upon a rather complex interaction among the muscular system, reflex cardiovascular and fluid volume systems and, much remains to be done in the research field.

I predict that hydrostatic compensation will fall off rapidly after insertion into orbit, due to body fluid redistribution, and plateau at some lower than normal level. It also would seem to be reasonable to accept this decrement until Mars approach before attempting reconstitution. Just as the Russians report for their MIR cosmonauts - prolonged sessions in the lower body negative pressure device herald to the cosmonauts their imminent return to mother Russia - our space crew approaching Mars might then use the lower body negative pressure device to regain lost hydrostatic compensatory ability.

Again much remains to be done for body fluid and blood volume restoration must be done at the same time if full compensation is to be regained. This is a complex field of interacting systems that require much more study before a Mars mission can be done.

Just as the Penguin-3 suit provides continuous stimulation to the muscles and bones in between exercise periods, extremity tourniquets, integrated into a properly designed, continuously worn suit, might provide considerable stimulus to circulatory responsiveness. One minute on, one minute off at thirty millimeters of mercury, just sufficient to impede venous return, might be an operationally acceptable means of maintaining hydrostatic reflex effectiveness.

As with everything else, this research field is wide open. Similarly, the lower body negative pressure device properly fitted into a sleep chamber and cycled continuously throughout each sleep period might be even more effective than extremity tourniquets to maintain circulatory responsiveness. Presumably some combination of periodicity and negative pressure can be arrived at which is sufficient to help and still be crew acceptable. Again, a fertile area for research.

If I seem to be coming back again and again to research opportunities, it is with intent because my first priority with this type of presentation is to try to direct research to support these glaring operational needs. If because of this talk one young researcher is motivated to investigate just one of these areas my hopes will have been satisfied.

BODY FLUID REDISTRIBUTION
Let us now direct our attention to body fluid redistribution and red cell mass because it is directly tied to circulatory orthostatic responsiveness. Recumbency studies long ago documented the fluid shifts that occur with positional change. Immediately upon assuming the recumbent position some six to eight hundred cc's of fluid are quickly transferred to the pulmonary reservoir and then to the circulation for excretion by the kidney. This is known as recumbency diuresis.

Obviously this same pattern of fluid shifts is inevitable initially upon achieving weightlessness. Indeed, investigators feel that this dynamic process may begin on the flight pad while crew members are awaiting launch. Echocardiographic studies from Spacelab document the rapidity of this hydrostatic adjustment. Venous pressure determinations revealed that as early as twenty-two minutes after launch, venous pressures had returned to normal or below, reflecting more than anything else the capacitance of the pulmonary reservoir.

Predictably, the net result of all this is a decreased circulating blood volume shortly after achieving orbit which must persist, more or less fixed, throughout the mission. This is pure zero gravity compensation and is perhaps irrelevant physiologically while in orbit. Only when one is nearing return of G loading does this become critical.

RETURN OF GRAVITY LOADING
It is in these last few hours of weightlessness that our medical support system must attempt to optimize body fluids and blood volumes of our Martian explorers. Perhaps the least desirable way is oral saline for it can be associated with nausea, anorexia, even vomiting and the results are unpredictable.

Intravenous saline solutions must be considered, with and without the concurrent administration of the mineralocortcoid, DOCA, but much research remains to determine the proper dosage and timing of these agents. Properly used, their ability to expand total body water and circulating blood volume is unquestioned.

Another drug having established importance in body fluid distribution is the anti-diuretic hormone, Pitressin. In recumbency diuresis and immersion diuresis I found that administration of this drug completely inhibited the response. Properly timed and dosed it might augment other measures for body fluid and blood volume restoration.

Total red cell mass must be calculated at this time. If diminished significantly, the crew members own blood, collected months previously, will be returned to their circulation. Blood doping is the designation for this procedure.

Return of G forces now is imminent. Lower body negative pressure and muscle strength tests done at this time will tell us how successful our preventive measures have been and permit informed decisions concerning crew member ability to meet operational requirements immediately upon contact with the Martian surface. For this phase of the mission our medical support system has provided chap type G-suits to help sluggish circulations to adjust once more to hydrostatic pressure.

Perhaps we must rest on motorized recliners for a few days, gradually getting our bearings. Perhaps additional hydrostatic support is required for which purpose we have designed a hydro suit as a back-up device. Small electric motors built into the hips, elbows and knees of such a suit might be required to assist anti-gravity muscles too weak for the job at hand. Perhaps these features will be integrated into the motorized recliner. Whatever is required, we would have anticipated and made available. We truly would have designed a medical support system for a Mars mission.

At this point, I should point out that safe return to Earth, many months later, of our crew members will place even greater demands on our medical support system. Nearly two years will have elapsed without their being challenged by normal gravity. Their ability to walk away from the recovery site is highly doubtful regardless of onboard countermeasures but our system will be able to meet their needs.

Fortunately on Earth we will have the support of our recovery team so we can accept a substantial loss of stress tolerance. Hopefully, by the time of our Mars mission, our ISS will have become a rotating wheel, offering our crew a choice of gravity and progressive reconditioning before return to Earth.

In conclusion I should like to support and emphasize the wise counsel of Doctor Grigoriev that it is unreasonable to expect to prevent completely the effects of prolonged weightlessness. This is a cost-effective decision, a balance between the ideal and the acceptable. We will tailor the medical support system to the needs of each mission. Much more research is necessary to give us the information required to design our system. Much can be done in earth based laboratories but the International Space Station is mandatory to further refine our data.

No Mars mission can be done until the weightlessness deconditioning challenge is resolved. It may be that our spacecraft engineers will have to face the necessity for artificial gravity for all extended missions such as Mars travel. Even our International Space Station must have artificial gravity to meet the needs of the future.
(Presented at the Mars Society meeting, Toronto, Canada, 12 August, 2000)

Duane Graveline MD MPH
Former USAF Flight Surgeon
Former NASA Astronaut
Retired Family Doctor

 

 

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