Oxygen is carried by the blood. When oxygen enters the lungs, it immediately dissolves into the blood, much like a spoonful of sugar dissolving quickly in water. The amount of dissolved oxygen in a normal person's blood is related to environmental pressure. Humans live in an environment with one atmosphere of pressure. Since oxygen in the air is only about 1/5 of that in the atmosphere, the amount of dissolved oxygen in human blood is very small and insufficient to meet the body's needs. Oxygen easily enters red blood cells and is transported with them. The amount of dissolved oxygen in the blood is small but crucial. Because red blood cells carry dozens of times more oxygen than dissolved oxygen, a normal person can meet their oxygen intake requirements.
For example, the hyperbaric oxygen experiment: In 1956, Dutch scientists conducted an experiment. Blood was drawn from a pig's artery and then injected into a vein with saline solution. The pig was then placed in a hyperbaric oxygen chamber with three atmospheres of oxygen. The pig survived for 15 minutes in this chamber. After the blood was reinfused, the pig was still alive. The pig continued to live by dissolved oxygen. Scientists named this experiment "life without blood." After numerous experiments, it was concluded that the amount of oxygen dissolved in the blood increases with the pressure of the hyperbaric oxygen chamber. Inhaling pure oxygen in a 2-atmosphere chamber increased the dissolved oxygen in the blood by 14 times, while at 3 atmospheres it increased by 21 times.
