Space flight is less demanding on the human body than deep diving

A short expedition into space is less of a challenge for the human body than diving at great depths, said Prof. Jacek Kot, an expert in hyperbaric medicine from the Medical University of Gdańsk.

On Tuesday, June 10, the Ax-4 space mission is to be launched from the Kennedy Space Center in Florida (USA) with Polish astronaut Sławosz Uznański-Wiśniewski on board. The mission crew also includes: Peggy Whitson (USA), Shubhanshu Shukla (India) and Tibor Kapu (Hungary).

"For a healthy person, a short stay in orbit is physiologically less taxing than a deep dive. If an astronaut has an accident on the International Space Station, they can be brought back to Earth within a few days. Meanwhile, to safely extract a saturation diver from a depth of even 100 meters, decompression lasting up to a week is needed," hyperbaric medicine expert Prof. Jacek Kot told PAP.

"Space medicine has been using the experience of diving medicine from the very beginning," said a researcher from the Medical University of Gdańsk. He explained that astronautics needed knowledge about how the body tolerates pressure changes, because they are usually the greatest challenge for travelers during extreme expeditions.

Prof. Kot reminds us that at the beginning of the space era – for example, during the Apollo program – the pressure on spaceships was reduced to the lowest tolerated by humans: only 0.26–0.3 atmospheres. The lightweight materials from which the ships were built were not strong enough to maintain pressure similar to that on Earth.

The reduced pressure, however, meant that astronauts had to go through a process of adaptation to the new conditions – this is called decompression. Moreover, in such conditions, ordinary air (20 percent oxygen and 80 percent nitrogen) becomes toxic, because the partial pressure of oxygen is too low to support life processes; therefore, astronauts had to breathe pure oxygen, which in turn is extremely flammable.

"Any spark, any overheating could lead to a fire. That is why in the history of cosmonautics, for example in the Apollo program, we had to deal with fires - both in space and on Earth, during training," described Prof. Kot.

He added that over time, they learned to build more durable vehicles. That's why for decades, manned space missions have maintained atmospheric pressure similar to that on Earth.

Today, an astronaut experiences pressure changes in only two situations: when the cabin is leaking or during spacewalks - in a spacesuit, where the pressure must be reduced to allow free movement. "This requires appropriate preparation, i.e. a decompression process, the same as for divers," the scientist explained.

While the body tolerates pressure increases relatively well, a rapid drop in pressure can be dangerous to health – it can lead to decompression sickness. Prof. Kot compares it to the sudden opening of a bottle of carbonated drink: gas bubbles that were dissolved in the liquid under high pressure are released from it rapidly. This is why the bottle should be opened slowly, not violently. During decompression, bubbles can form in the joints, muscles, blood, and even the brain or spinal cord, which can lead to decompression sickness, sometimes called decompression sickness – it can be associated with joint pain, paralysis, and even loss of consciousness. Treatment – ​​reduction of air bubbles – takes place in a hyperbaric chamber.

Saturation divers, who work for weeks at elevated pressure, need 100–200 hours (i.e. 4–8 days) of decompression to get out of a depth of 100 meters. Prof. Kot explained that such divers usually never sleep underwater – they are taken from their workplace to the surface in diving bells, under constant pressure. The decompression process itself takes place in hyperbaric chambers.

This means that if such a diver suffers a heart attack, an attack of appendicitis or other serious injury, it will take several days before he reaches the hospital. Meanwhile, an astronaut can be evacuated from the space station in favorable conditions even on the same day, the researcher emphasized.

"In diving, every 10 meters of depth means an increase in pressure by one atmosphere," explained Prof. Kot. He added that "at a depth of 100 meters, the pressure is therefore ten times higher than on the surface." As he emphasized, such large pressure changes are not experienced during space flights.

The physiological challenges associated with diving concern not only the pressure, but also the composition of the gases that divers breathe. "A regular air mixture becomes dangerous even at moderate depths. Too much oxygen damages the lungs and even the brain. And nitrogen causes an effect similar to alcohol intoxication, known as the 'Martini effect'," the expert said.

The deeper you go, the more complicated the breathing mixtures become. Professional divers use gas mixtures (oxygen, nitrogen, helium, and even hydrogen) tailored to a specific depth. However, even these mixtures – dissolving in the body – pose a risk of decompression sickness on ascent.

As emphasized by Prof. Kot, diving at great depths is still a greater challenge today than traveling to orbit. "While space flights are more or less mastered from the point of view of human physiology, diving to greater depths – absolutely not. It is still a huge challenge. Space is fascinating and its exploration is difficult, but diving is even more difficult and even more taxing for the body," the researcher concluded.

Science in Poland, Ludwik Tomal

lt/ bar/ amac/