It's incredible that there have been more astronauts on the Moon than divers who have dived at altitudes over 5500 meters above sea level. Due to the rarity and lack of data on decompression under such conditions, each dive at these altitudes is experimental. Very little is known about the human body's response to increasing water pressure at extremely low atmospheric pressure.

The Nevado Tres Cruces MedExpedition 2015 aimed to perform dives in Lake Tres Cruces Norte, located in the crater of the extinct volcano of the same name, at an altitude of 5915 meters above sea level. It is one of the highest volcanoes, situated on the edge of the driest region in the world, the Atacama Desert on the border of Chile and Argentina.

The expedition's goal was not so much to achieve a sports objective, such as diving in one of the world's highest lakes and breaking the Guinness high-altitude diving record, but to gather data on the physiology of diving under such conditions. The person responsible for this part of the project was Patryk Krzyżak, a doctor of medical sciences and a diver, who took care of the scientific aspect of the project.

As usual with such expeditions, logistics proved to be a huge challenge and required many months of planning and arrangements with local companies that could assist in the expedition. Obtaining nitrox and having to send tanks from a base over 800 kilometers away was a significant problem.

The expedition set off on February 22, 2015, and after 38 hours of travel by plane and car, it reached Copiapo in Chile, from where it was to depart by 4x4 through the desert to the foot of the volcano. The weather filled the team with apprehension, as low cloud cover and frequent precipitation suggested that heavy snowfall might occur in the higher parts of the mountains, preventing access to the site. Fortunately, after crossing the pass at an altitude of 4150 meters, where a view of the "Three Crosses" opened up, it turned out that the weather had significantly improved, giving hope for success.

From February 26 to March 3, the team conducted acclimatization and reconnaissance. The relatively gentle slopes of the volcano gave hope that part of the route to the summit could be conquered by 4x4, which would greatly facilitate the transport of the heavy equipment needed for diving. After many attempts, a relatively gentle slope was finally found between two ravines, allowing the team to reach an incredible altitude of 5175 meters. And that meant that the equipment had to be carried only 750 meters high. Not much, but still a huge effort considering the thin air at that altitude.

After a relatively short acclimatization, the team decided to attempt the ascent. The equipment was partially transported by local porters, who joined the expedition on March 6. The lake is located in a crater, so moving the equipment to its edge required crossing the pass between Tres Cruces Norte and Tres Cruces Central, and then descending to the crater floor.

Finally, on March 11, 2015, the expedition was ready to dive. The dive was conducted in sidemount configuration, lasted 23 minutes, and reached a maximum depth of 11 meters. It may not seem like a big challenge, but one must consider the much lower pressure at the surface than at sea level, as well as factors such as fatigue from climbing and the possibility of altitude sickness.

The team was constantly monitored, and Patryk Krzyżak collected data on aspects such as heart function. The dive itself allowed the collection of a unique and extremely valuable set of data on the impact of atmospheric pressure at the dive site on the diver's body, as well as the rate of gas saturation and decompression.