AVOIDING HEART FAILURE IN SPACE
During the radio blackout of reentry, on Apollo 15, necessitating a recording, Irwin described in his autobiography , classical symptoms of angina, but also symptoms consistent with acute congestive heart failure, at 7 G's : "It was amazing to me that Dave was able to talk to mission control while we were coming in. I couldn't take a breath. I was living on the residual oxygen in my lungs. It felt like an elephant was standing on my chest. Couldn't move the diaphragm."(1) Twenty-one months later Irwin experienced a heart attack. (2)
Despite invariable dehydration with space flights, there is the potential for congestive heart failure complicating potential oxidative stress injuries of the lining of the blood vessels (endothelium), associated with impairment of endothelial function (3).
One of the major players responsible for potential oxidative stress insults to the endothelium is a specific cytokine- a peptide which regulates immune mechanisms - called tumor necrosis factor ( TNF) .When certain cultured bone marrow cells which produce TNF are stimulated in space on 6 and 9 day missions, they secrete significantly more TNF than when they are stimulated on earth.(4)
This portends a profound therapeutic dilemma because atherosclerosis, we now know, is an inflammatory disease and TNF, a mediator of vascular inflammation, plays a major role in triggering oxidative stress and TNF is conducive to congestive heart failure.(5)
Furthermore with space flight -related malabsorption and also progressive loss of storage sites for magnesium in bones and skeletal muscles, TNF levels will progressively increase as the magnesium levels fall. This is compounded by several self-sustaining vicious cycles , since TNF induces also both bone resorption and deterioration of skeletal muscles (4,6) in addition to the deterioration of both triggered by space flight.
How can space-flight related congestive heart failure be prevented? I have emphasized that one consideration is the prevention and correction of magnesium deficits which might prevent in turn cardiovascular complications of even young (under age 30 ) astronauts during the mission. I have pointed out that for the most part, pharmaceuticals are contraindicated in space because of invariable malabsorption, necessitating parenteral drugs, deterioration of some pharmaceuticals possibly because of space flight radiation, and potential inability to metabolize and excrete pharmaceuticals because of potential hepatic and renal functional impairment .complicating particularly long missions. A stable subcutaneous magnesium product can be produced (magnesium -1-aspartate -hydrochloride)( personal communication, H G Classen ) but a replenishable subcutaneous delivery device must be developed.(6).
Finally it seems reasonable to take advantage of the estrogen- induced increased uptake of magnesium in skeletal muscles and bones in the presence of space flight- related marginal intakes in young females in comparison to their male counterparts, particularly for very long space missions. (7) In addition a paper -just published- emphasizes the new discovery of an additional vascular protective function of estrogen regarding the effects of TNF receptors providing advantageous effects on the vasculature in the presence of ischemia; this may be the underlying mechanism related to the lower incidence of heart failure and higher heart failure survival in females on earth. (8).
William J. Rowe M.D. FBIS