Before any spacewalk, astronauts must purge nitrogen from their blood as it is a major component of the body’s blood pressure. Without nitrogen in their blood, astronauts would be more likely to develop decompression sickness, also known as ‘the bends’, when they return to Earth’s atmosphere. Nitrogen in the atmosphere is 78% N2, while N2 makes up only 20% of the human body. When you breathe normally, the N2 in our blood dissolves into our bloodstream, creating a higher concentration of N2 in our bloodstream than normal atmospheric pressure. When astronauts return to normal atmospheric pressure after a spacewalk, the extra dissolved N2 in their bloodstream will cause them to become decompressed. This can lead to decompression sickness. In preparation for a spacewalk, astronauts will spend time in a hyperbaric chamber, where they breathe pure oxygen and undergo decompression procedures that can last up to 12 hours. The purpose of this is to flush out the excess nitrogen (N2) from their blood before going on a spacewalk.
Nitrogen is a major constituent of both blood and bodily tissue, so before a spacewalk, astronauts have to purge nitrogen from their blood. They do this by breathing 100% oxygen for about an hour, which causes all of the nitrogen to be replaced with oxygen. If they didn’t do this, the body would have to deal with two different types of molecules (nitrogen and oxygen), and it would be very dangerous because each molecule has a different boiling point. After purging all the nitrogen from their blood, astronauts can then safely go outside without any risk of decompression sickness (DCS). DCS develops when nitrogen bubbles form in the body, usually in the blood vessels that branch off into the joints and the spinal column. When these bubbles burst, they cause excruciating pain, and sometimes injury to the tissues nearby. This is one reason why it’s so important for astronauts to stay hydrated during spacewalks; otherwise their bodies could become dangerously dehydrated, which could result in DCS. Being well-hydrated also helps prevent cramping, which is another serious risk during spacewalks.
Nitrogen is a major component of Earth’s atmosphere and it’s also the most abundant chemical element in the solid earth. However, in the presence of sufficient oxygen, its toxicity is what makes it so dangerous. In the human body, nitrogen can have both toxic and lethal effects on nerve tissue. Humans need to prevent blood from turning into gas during the space walk so that it doesn’t deform their bodily organs. As such, the changing pressure of nitrogen during a spacewalk can cause an embolism in the blood vessels if unaddressed. This is why astronauts need to purge nitrogen from their blood before a spacewalk.