“Breathing is one of the most important and vital acts we do.”
So says the Guys and St Thomas’s Hospital website, and so it must be true. Breathing is important– and anything that hampers breathing is potentially disastrous for us.
Like so many bodily functions we take breathing for granted. We do it without thought and yet, unlike many bodily functions, we can control it, to a limited extent. It is both voluntary and involuntary. We can’t hold our breath indefinitely of course (the record for breath holding is 24 minutes and that was achieved by a man breathing pure oxygen for a while beforehand and then lying very still at the bottom of a warm swimming pool), our automatic override kicks in for most of us after about a minute, which is a bit poor compared to seals and whales. It’s the CO₂ that makes us breathe out after holding our breath, rather than in, because CO₂ is a toxin and we can’t tolerate high concentrations of it. Every two minutes all the blood in our body goes through our lungs to have the CO₂ scrubbed away and replenished with fresh oxygen, over an area of glistening tissue that measures about 1,000 square feet.
Every day we breathe about 20,000 times, and in every breath we breathe in roughly 25 sextillion oxygen molecules (2.5 x 10²²). In one day we breathe in at least one molecule of oxygen from the breaths of every person who has ever lived. So you can see how a respiratory pandemic might be a little hard to deal with. On the plus side our respiratory system is very good at filtering out foreign bodies and cleaning itself. What doesn’t get caught and thrown back out by coughing and sneezing is shepherded back into the stomach by wafting hairs called cilia and dissolved there by hydrochloric acid. And then there are the macrophages, tiny cellular demolition teams that seek out and devour most of the things that get past before they can make us ill. But some get through, and sometimes the macrophages can go into overdrive and release too many chemical messengers called cytokines which can also make us ill (those of the Covid-induced cytokine storm). C’est la vie.
The diaphragm, located below the lungs, is the major muscle of respiration and peculiar to mammals. It is a large, dome-shaped muscle that contracts rhythmically and continually, and most of the time, involuntarily. On inhalation, the diaphragm contracts and flattens and the chest cavity enlarges. This contraction creates a slight vacuum, which pulls air into the lungs. The lining of the lungs, the pleural cavity, also has a slight negative pressure which helps stick the lungs to the outside of the chest cavity so that when we breathe out they don’t just collapse.
On exhalation, the diaphragm relaxes and returns to its domelike shape, and air is forced out of the lungs. It also makes our abdominal wall expand and contract. The abdominal wall is not usually used much in respiration but can be used to forcefully exhale. Coughing, sneezing, breathing on your glasses, and blowing out the candles on your birthday cake.
There are lots of other muscles involved in breathing. The intercostals between our ribs help the rib cage to expand and contract, and there are many other accessory muscles: the sternocleidomastoids and the scalenus anterior in the neck which lift the top of your rib cage (Christopher Reeve used these to breathe unaided for a scene in the film Rear Window), the pectoralis major and minor in the chest which help you breathe in but not out, the serratus anterior in your sides, and latissimus dorsi in your back (the ‘lats’) that help the lower ribcage expand, and a few others besides. Technically any muscle attached to the upper limb and the thoracic cage can act as an accessory muscle of inspiration.
Our breathing alters in pattern and rhythm at different times of the day and in different situations. Muscular breathing in the upper rib cage is useful when we need to really expand our breathing – when doing hard physical work or running for example. In some emotional states these muscles can also dominate, when sighing for example, or in that fluttery kind of sobbing when the air barely gets down the trachea. When this chest breathing happens on its own it is often associated with stress, and the shallow breathing that goes with it reduces our oxygen supply. We also have a propensity to stop breathing altogether in fear or pain, and during childbirth for example (for the mother anyway). No one seems to know why, as it isn’t very helpful.
Conversely deep ‘belly breathing’ is associated with rest and lowered stress levels and this is why it can do us so much good, helping the mind and body into a relaxed state. But it needs regular practice to be effective. Sure we can do it naturally when we’re not thinking about it, but when we are stressed it’s not so easy. It shouldn’t be forced, and the ribs still have to move a little, especially lower down, otherwise the abdominal wall can move without deepening the breath and the benefit is lost.
With thanks to Bill Bryson and his 2019 book ‘The Body’