In 1828 it took 8 months for the young doctor William Fraser Tolmie (1812–1886) to sail from Scotland to the Pacific Northwest to assume his combined medical and fur-trading position with the Hudson’s Bay Company. Now NASA is planning to send a group of astronauts to Mars—a trip that may also take about 8 months. The big difference will be that instead of being tossed around on the ocean, the astronauts will be flying at supersonic speeds through space in weightlessness.
While boredom and sea sickness were problems for the ocean voyagers, the astronauts’ problems might include space motion sickness, headaches, nausea, blurred vision, reduced motor and cognitive ability, as well as discomfort from puffy faces and thinner legs.
Studies investigating why the face becomes puffy in space, and why headaches occur, have been conducted on volunteers who were put through a number of special low-gravity producing airplane flights. Early results seem to confirm that the lack of gravity during these special flights leads to an increase in blood flow to the head and a shift of cerebrospinal fluid toward the brain. The fluid shift probably overwhelms the blood-brain barrier, causing brain swelling and increased intracranial pressure, which results in reduced oxygen supply to parts of the brain.
The cause of the unexpected fluid dynamics is attributed to nitric oxide (distinct from nitrous oxide, the laughing gas). Nitric oxide was discovered in the 1970s by three American pharmacologists, Robert Furchgott, Louis Ignarro, and Ferid Murad, who were rewarded with the Nobel Prize for Physiology or Medicine in 1988. Nitric oxide is a gaseous molecule that is released by the endothelium of blood vessels in response to increased heart pumping action. It becomes dissolved in the blood, influences many cellular functions, expands blood vessels, and decreases plaque activity and blood clotting. It may act as a vasodilator and a modulator of vascular tone and blood pressure. The “nitro” component is used as therapy for angina, pulmonary hypertension, and other vascular disorders.
Scientists are now working on drugs that may counteract the increase of nitric oxide in the blood when astronauts are in a low-gravity environment. Another tactic to help pull blood away from an astronaut’s head is to create negative pressure in the lower half of the body. One proposed way to do this is with rubber suction trousers. It is an interesting idea, but the inventors must keep in mind what an increased concentration of nitric oxide trapped in blood vessels might do.
As an example, sildenafil (Viagra) works by influencing enzymes that enhance the nitric oxide content of blood flowing through a specific organ. The increased blood flow into the erectile tissues causes genital tumescence. While suction trousers sound inventive, and may save the brain, the nitric oxide–related side effects on the lower body might just add one more problem to the weightless male astronauts’ 8 months of travel to Mars. There is no comparable data for female astronauts in a low-gravity environment.
—George Szasz, CM, MD
Bailey D. What happens to the brain in zero gravity? The Conversation. Accessed 11 December 2018. http://theconversation.com/what-happens-to-the-brain-in-zero-gravity-106256.
Moncada S, Higgs EA. The discovery of nitric oxide and its role in vascular biology. BJ Pharmacol 2006;147 Suppl 1: S193-201.
This posting has not been peer reviewed by the BCMJ Editorial Board.