Breathing is ideally a process of maximum efficiency with minimum effort. Its efficiency depends on the correct functioning of the diaphragm, a strong sheet of muscle that separates the heart and lungs from the abdomen. Each breath starts in response to a message from the respiratory center in the brain which causes the diaphragm to activate. It flattens into a disc, making the lower ribs swing out and thus increasing the volume of the chest cavity. The lungs follow this expansion, creating a partial vacuum that pulls air into the lower lungs, much like a bellows.
When we exhale, the diaphragm simply relaxes. The lungs have a natural recoil that allows them to shrink back to their regular size and expel air. The abdominal muscles and muscles of the rib cage can enhance this process, but it is the release of the diaphragm and the recoil of the lungs that are the crucial elements in the exhalation. After a pause, the breath cycle begins again, a pumping rhythm we can all easily feel. When our breathing apparatus is working efficiently, we breathe six to 14 times per minute at rest. In a healthy person, this rate increases appropriately when the physical needs of the body require it.
Waiting to Exhale
Like other involuntary bodily functions, breathing is usually controlled by the autonomic nervous system, which enables the human organism to run like a well-oiled, self-correcting machine. There are two branches to this system: the parasympathetic and sympathetic. The parasympathetic branch, known as the "relaxation response," controls resting functions of the body. It slows the heart and breathing rate and activates digestion and elimination.
The sympathetic branch has the opposite effect. It rouses the body and regulates active functions related to emergencies and exercise. When emergencies arise, the sympathetic branch floods the body with adrenaline—the well-known "fight or flight" response. The heart rate goes up and breathing rate increases to supply the body with an infusion of oxygen. If the danger is real, the increased energy is used. If not, the body stays in a state of overstimulation which can become chronic, causing a number of symptoms including anxiety and hyperventilation (overbreathing).
Since few of us are immune to the constant stresses and strains of modern life, the alarm bells of the sympathetic nervous system are constantly being rung. It is a real juggling act to maintain a healthy autonomic balance, a challenge at which asthmatics generally fail.
Although most asthmatics are unaware of it, we tend to chronically breathe at a rate two to three times faster than normal. Paradoxically, instead of providing more oxygen, overbreathing actually robs our cells of this essential fuel. We do take in more oxygen when we overbreathe; but, more importantly, we also breathe out too much carbon dioxide.
Most of us learn in school that when we breathe we expel carbon dioxide as a waste gas, but we don't learn that expelling just the right amount of CO2 is critical for healthy breathing. If CO2 levels get too low, the hemoglobin that carries oxygen through the blood becomes too "sticky" and doesn't release sufficient oxygen to the cells.