SPACE TOURISM AND HYPERTENSION Spaceflight 52: 113, 2010.

Recently as a guest on the SPACE SHOW ( www.femsinspace.com ) I was asked whether there is a significant risk of entering space by engaging in a suborbital flight of only 2 hours to an altitude of about 63 miles, if a passenger with hypertension took their medications prior to the mission. This is a very important question since approximately 1/3 of the population above the age of 35, has blood pressure above the ideal level of 130/80 mm Hg.

My response was that it would be risky even if that passenger’s blood pressure was maintained in the ideal normal range throughout most of the mission with the exception of the period during reentry when the peripheral resistance would be significantly elevated to perhaps 3 G’s (the approximate reentry G forces of the shuttle). I also stressed that it would be foolish to withhold the information regarding the space flight (SF) from one’s physician because of the potential risk.

Hypertension is associated with generalized dysfunction of the endothelium ( lining of the blood vessels) (1) and therefore those with hypertension are at risk of an acute vascular insult anywhere in the body as for example a heart attack particularly during reentry.

Individuals with hypertension tend to have high heart rates (2-5) which in turn can precipitate a fatal heart rhythm disturbance when exposed to stress (6). For example Irwin, the lunar module pilot on Apollo 15 had hypertension (145/110) shown a month prior to the mission, and developed an arrhythmia for about 30 seconds with brief loss of consciousness while transferring gear from the lunar to the command module. (1) In addition-- associated with his hypertension-- he might be considered a “hot responder “ suggested by the fact that 3 years before Apollo 15, Irwin’s heart rate climbed to 180/ min. in comparison to Gibbon’s rate of 150/min. during the manned test of an Apollo spacecraft in a fully pressurized oxygen atmosphere (5). During the first lunar excursion – prior to inhalation of dust brought in on the spacesuits in the lunar habitat – Irwin’s heart rate climbed to 167/min. while Scott’s heart rate remained < 130/min. while configuring the lunar rover.

Both hypertension and space flight are associated with elevations of adrenaline. Until a few years ago the adrenaline levels were not felt to be elevated but in fact plasma levels of adrenaline with SF have been shown to be approximately twice the value of the supine levels on earth ( 7 ).

Although it is unlikely that magnesium ion levels would be significantly decreased as a result of such a short 2 hour SF the adrenaline levels may be further elevated from a magnesium (Mg.)ion deficit ( very common in our western society )prior to lift-off with a vicious cycle between decreased Mg. ions and elevations of adrenaline. In the presence of a Mg. deficit there is the potential for another vicious cycle via the kidneys. A Mg. ion deficit, prior to lift-off, would also be conducive to 2 other vessel constrictor elevations, shown to be elevated with both SF and a Mg. ion deficits i.e. angiotensin and endothelin.

Finally, a very important vessel dilator and clot buster (atrial natriuretic peptide) (ANP) may be reduced with a Mg. ion deficit because Mg. is necessary for the release and probably the synthesis of this vital peptide (ANP)(8) so that in the presence of a Mg. deficit there is another potential mechanism for clot formation and blood vessel constrictions with risk particularly of stroke or heart attack.

William J. Rowe M.D. FBIS
rowerun@aol.com

References

1. WJ Rowe. Extraordinary hypertension after a lunar mission. Am J Med, 122, p. e1, 2009.
2. S Takishita. The sympathetic nervous system in essential hypertension : pathophysiological signifigance. Int Med, 40 pp 151-153, 2001.
3. S Julius , P Palatini , SD Nesbitt. Tachycardia : an important determinant of coronary risk in hypertension. J Hypertens Suppl, 16, pp S 9-15, 1998.
4. TB Tjugen , A Flaa , SE Kjeidsen. High heart rate as predictor of essential hypertension : the hyperkinetic state , evidence of prediction of hypertension , and hemodynamic transition to full hypertension. Prog Cardiovasc Dis, 52. pp 20 -25, 2009.
5. WJ Rowe. Moon dust may simulate vascular hazards of urban pollution. JBIS, 60, pp 133-36, 2007.
6. X Jouven, J-P Empana, P J Schwartz, M Desnos, D Courbon, P Ducimetiere. Heart-rate profile during exercise as a predictor of sudden death. New Eng. J Med, 352, pp 1951-58, 2005.
7. WJ Rowe. Potential renovascular hypertension , space missions, and the role of magnesium. Int J Nephrol and Renovasc. Dis, 2, pp 51-57, 2009.
8. NLM Wong, DCK Hu , EFC Wong . Effect of dietary magnesium on atrial natriuretic peptide release. Am J Physiol , 261, pp H 353-H 357,1991.