To provide this increased pressure one must be completely inside a pressurized room, a hyperbaric chamber. Oxygen breathed while inside a hyperbaric chamber is no different from natural oxygen. It is natural oxygen, only delivered in a pressurized chamber. The increased pressure does not change the molecular composition of oxygen. Increased pressure allows oxygen to get into tissues better.
Extra pressure improves oxygen flow in the blood.
The limit that one gram of hemoglobin can combine with oxygen is 1.34 milliliters. Red blood cells can only deliver a limited level of oxygen to tissue cells, a pO2 of 39 mmHg or less. As we age we can loose vital lung capacity and the ability to effectively obtain adequate oxygen. Some disease conditions impair oxygen utilization. Also, injuries or conditions with swelling can cause pressure that cuts off circulation flow.