Oxygen is one of the essentials for life - 3 minutes is the approximate time the average person can survive without air. Without sufficient oxygen, your body tissues will die. Breathing is the natural process of providing the lungs with air where oxygen is converted for use by the cardiovascular system. The muscle contractions responsible for breathing is an automatic function that is regulated by the medulla part of the brain, but how how fast and how deeply we breath can be shared by the medulla and our conscious attention. Athletes for instance are trained to control their breathing as a way to improve their performance.
Many of us lead very busy lives with family and work that require our attention and keeps our nervous system in an almost constant sympathetic state - ready for a fight or flight response. When the sympathetic nervous system is dominant your breathing is altered to short and fast breaths so that your body can put energy into fighting or running away. Over time we become accustomed to the heightened state of readiness and find it difficult to relax - we react from the sympathetic state as if each situation requires a fight or flight response. One way to absorb more oxygen is by using a hyperbaric oxygen chamber and an oxygen concentrator.
Research shows that "At 2.0 ATA, the blood oxygen content is increased 2.5% and sufficient oxygen becomes dissolved in plasma to meet tissue needs in the absence of haemoglobin-bound oxygen, increasing tissue oxygen tensions 10-fold (1000%) [Staples and Clement, 1996]."