| Spaceflight Vol 45:88, 2003
|William J. Rowe, MD is a retired internist-cardiologist with several publications over the past 10 years, involving the vulnerability of the normal heart to space-related injuries and how to avoid them.|
Suppose you lived in a city with inadequate rainfall. Furthermore, suppose the reservoir was not large enough to meet the needs of the population. Finally, suppose for the most part the citizens were unaware that these problems even existed! That is the dilemma those on space flights face, regarding both depleted water and magnesium reservoirs.
Research conducted by the American College of Sports Medicine, and sponsored by NASA in 1995 concluded that "in spite of a variety of countermeasure protocols, there are presently no activity-specific countermeasures that adequately prevent or reduce musculoskeletal deficiencies" Because of decreased thirst and absence of skeletal muscle symptoms until return to earth, astronauts are unaware that the reservoir for water in the muscle and the reservoir for magnesium in the muscle and bone (about half in each) has shrunk. In addition magnesium deficiency is usually silent.
With the loss of water and magnesium, the body begins to lose its antioxidant protection within a few days and with it, protection against free radicals. These are highly energetic pieces of molecules with an unpaired electron making them highly reactive and unstable, highly oxidizing which means that they have a strong attraction for hydrogen and enough energy to break hydrogen bonds., They can split DNA apart.
Water is a useful antidote to free radical damage because of the hydrogen atoms it contains. The oxidation caused by free radicals can injure the cardiovascular system, and other vital organs with an accelerated process in space similar to the aging process.
Magnesium in addition to water, is also an antidote to free radical injuries and serves as "nature's calcium blocker;" thereby it reduces the potential for excess shift of calcium into the cell, which may injure its energy producing machinery. Sufficient magnesium may prevent clot formation, with spasm of the coronary and peripheral vessels, heart rhythm disturbances and a life threatening heart attack.
On Apollo 15 (a 12-day mission in 1971) I postulated that even prior to lift-off, ie prior to depletion of the reservoir, the crew was likely to have a magnesium deficit, because it trained in "intense summer heat." Both Irwin and Scott on the lunar surface, experienced severe pain of the fingertips, which I postulated could have resulted from magnesium deficiency-related spasm of the vessels of the fingertips, and could serve as a warning that coronary vasospasm (possibly silent) could also exist (the Apollo 1 5 Space Syndrome). Irwin lost consciousness for a brief period associated with a rhythm disturbance after leaving the lunar surface and during reentry suffered symptoms consistent with angina and congestive heart failure. A contributing factor was severe dehydration, particularly in Irwin’s case, from failure of the in-suit water devices. Twenty-one months later Irwin had a heart attack.
Experimental animals after only a few weeks in space, show changes of the heart muscle consistent with a magnesium deficit, destruction of the energy machinery of the heart muscle cells, and impairment of the repair processes.
Since magnesium deficits have been shown in astronauts on even short missions of a few weeks, what measures can be taken to prevent magnesium and water deficits on a mission to Mars with the reservoirs approaching empty? A partial correction of the depleted water reservoir can be accomplished merely by forcing fluids, thirsty or not. But with magnesium deficiency the problem is far more complicated.
Until a few years ago there wasn't a relatively simple, sensitive test to measure magnesium. Deficits demonstrated after even relatively brief space missions probably often represented "'the tip of the iceberg." But recently, B.B. Silver developed a new technique, measuring magnesium levels in the tissue under the tongue, by obtaining cell smears as simply as a gynecologist obtains Pap smears. These can be run daily and the accuracy matches tissue magnesium levels obtained from the heart at open-heart surgery.
The magnesium reservoir would be expected to be larger in young females over their male counterparts, because young females retain magnesium to a greater extent than young males when the magnesium intake is marginal. Mildred Seelig emphasized over three decades ago that natural estrogen’s enhancement of magnesium utilization and uptake by soft tissue and bone, may explain the resistance of young women to heart disease and osteoporosis.
If excess calcium is administered to try to reduce the potential for osteoporosis, the subsequent excessive release of adrenaline will aggravate a deficiency of magnesium and defeat the purpose since magnesium is also effective in preventing osteoporosis.
But with malabsorption complicating space missions because of primarily microgravity, how can a magnesium deficit be prevented or corrected? A high magnesium diet, and oral supplements will not suffice. Intramuscular magnesium is painful. The only solution for prolonged space missions appears to be by the development of a suitable subcutaneous product, H.G. Classen has had experience with such a subcutaneous product for over 20 years in experimental animals and it is his opinion that a suitable magnesium product for humans with tissue tolerability for space missions could be developed.
J.T. Santini and colleagues have come a little closer to a possible solution for a reservoir, particularly for a long mission in the form of a controlled-released solid-state silicon microchip. This can provide multiple chemical substances on demand, initiated by electrochemical dissolution of thin membranes, covering over a thousand microreservoirs. The apparatus could be made the size of a pocket watch and placed in the subcutaneous tissue of the chest or abdomen. Experimental animal studies are being conducted at this time. A major stumbling block however appears to be that once the device is manufactured with the desired chemicals, ie magnesium and various electrolytes for example, there is no way to replenish it.
Such a device as Santini's, opens the door for consideration of other artificial reservoirs which can be replenished repeatedly and with the port not becoming displaced as in the case of the pump,
As of now the "reservoir" isn't ready for liftoff. Until then clearly we are not ready for a manned mission to Mars.