How marvelous it is that from birth thru death we breathe so well! Our autonomic nerves flawlessly activate and relax our diaphragms in tune with our brain’s assessment of how much CO2 waste has built up in our blood. Even if we hold our breath or exercise, blood oxygenation stays plentiful, so it never plays a role in our drive to breathe. Upon cessation of exercise, we have absolutely no need to inhale extra oxygen. We hyperventilate solely to rid our blood of the CO2, which has built up and caused a slight acidification of our blood.
In the relaxed state, our left and right diaphragms are domed. Think of cutting off a third of a round cantaloupe, and placing it next to another third of a cantaloupe; our diaphragms are like their rinds. All the muscle fibers radiate outwards and downwards from the fibrous tissue at their peaks. When these muscles activate and shorten, our diaphragms flatten and push downwards (‘south’, if you will); the chest cavity enlarges and air naturally rushes in to fill the extra space. To make room for more air, the diaphragms have pushed the stomach, liver, and intestines down and out; the relaxed belly wall allows itself to be passively pouched out.
When all the radial muscle fibers in our 2 diaphragms then relax, the shape of the diaphragms again become domed, our belly circumference shrinks, and the stale air in our lungs, beefed-up in CO2, is naturally, passively and effortlessly exhaled. During sleep or relaxed breathing, exhalation tends to be 50% to 100% longer than inhalation. Lately, an effective way for me to relax and be in the now is to mentally count to 4 on inhalations, and gradually increase the length of my exhalations from 4 counts to 8 counts. . . while I also try to focus on the position of my diaphragms.
Occasionally (e.g. with a sigh) we use the muscles outside of our chest to lift our ribs outward and upwards. This is the 2nd, but relatively unimportant way to increase the potential space that air can fill in our lungs.
Occasionally (e.g. when blowing up a balloon) we forcefully contract our chest wall muscles to expel air. And rarely, if we choose, we can forcefully contract our abdominal wall muscles to push the liver, stomach ‘north’ into the chest, so that the diaphragms are forced back into their fully-domed shape.
But the lion’s share of our breathing is due to gentle contraction and relaxation of the tireless radial fibers in our 2 diaphragms in response to the CO2 buildup in our blood. How often are we grateful for our behind-the-scenes diaphragm muscles? Can we sense their changing shape? It’s quite difficult, but like most things in life, we can get better with lots of practice.
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