I don't often watch the TV news, but on Monday last week I didn't feel like doing much else after work. Anyway, about 1/3 of the way through a story came on that had my critical radar twitching. It was effectively a puff piece about how employers were sending their workers on a course teaching them how to breathe properly, in order to oxygenate their brains & consequently think better & suffer less stress. The item showed a guy being fitted with some sort of sensor & receiving messages on his cellphone instructing him to breathe at a particular rate. We were informed that using this technique would maximise oxygenation of your brain, with a whole range of benefits following on from this.
Well, quite apart from the fact that any benefits wouldn't accrue to the brain alone, I found the article rather irritating. (Although, to be fair, on that particular day I might have found a whole lot of things irritating.) Because - I couldn't really see that there was much in it, & yet people were paying for advice along the lines of 'in times of crisis/stress, a deep breath will help you think more clearly'. I'll admit that I'll take a deep breath before answering if I'm put on the spot - but because it gives me time to think of an answer, not because I think it'll do much for the oxygenation of my brain. (Incidentally, there's no reason why that blood would all be channeled to your grey matter in any case.)
But in addition to this, control of our gas exchange system has been shaped by millions of years of evolution to give optimal oxygenation. Control of breathing rate is influenced by changes in the levels of CO2 in your blood (rather than oxygen concentration), as measured by a part of the brain called the medulla oblongata. As cellular respiration rates increase (due to increased activity), this generates more CO2, & this in turn triggers an increase in breathing rate. (I remember being quite excited when I found out that this was how haemoglobin 'knows' where to release its oxygen - the trigger is local changes in pH/CO2 concentration as a result of cellular respiration.)
So I'm just a leetle cynical (although happy, as ever, to be proved wrong!)