Did you know that most of us have two nostrils? It’s strange — we have a single trachea, but it branches into two pathways up top, and furthermore, those two terminal pathways are elaborate and mazelike, with a network of sinuses and these convoluted turbinate bones taking up much of the space behind your nose. I’d always just chalked it up to a side effect of bilateral symmetry (eh, you know, developmental biologist), but at the very least, it does have physiological consequences. Among those consequences is that there is a nasal cycle. You don’t breathe in equally through both nostrils, there is an alternating rhythm.
Try it yourself right now. Consciously consider what you feel as you breathe in and out normally — you probably can detect that one nostril seems a little bit more open than the other (if you’ve got a cold or allergies, your perception of this phenomenon may be messed up. Sorry. Get better soon.) As I sit here, for instance, I can tell that my right nostril has somewhat freer airflow than my left. It’s not that I’m having any problems breathing through either, it’s a subtle difference, simply a small, barely detectable asymmetry that is unnoticeable except when I’m consciously thinking about my breathing.
The cool thing about it, though, is that it alternates with a cycle length between about half an hour and 8 hours. The mechanism for that is that a portion of your septum and your inferior turbinate are covered with erectile tissue that becomes gradually engorged in response to sustained airflow, and relaxes as airflow is reduced, so your nostrils take turns getting aroused by breathing and then swapping off with each other to relax and recover.
You can measure the nasal cycle in a precise and continuous way with scientific instruments, if you’d like, but there’s also a rough and ready way. This weekend my wife and I drove to a meeting in Glenwood, and then on to Minneapolis, so we had a couple of long drives together, and we were talking about respiratory physiology, as one does, when I explained about this nasal cycle thing, and we decided to measure it. Since we didn’t have access to an electronics lab in the car, we did a subjective estimate: every half hour, we’d just try to be consciously aware of our breathing and report which nostril was doing most of the work. It beats playing Slug Bug, anyway.
So we did a day’s worth of crude measurements. One problem right away was that Mary was a bit congested and stuffed up, which meant the whole day went by with no change for her, which was a bit boring. She did finally detect a shift that evening, so her nasal cycle was estimated to be a bit longer than 8 hours. Another slight problem is that we also took our son and his girlfriend out to lunch, and mid-meal we had to announce “Nostril check!”, which meant we got some funny looks. But that’s OK, I’m used to getting funny looks.
As for me, I’ve gotten over a nasty cold that had been afflicting me for a while, so my face and sinuses and nasal erectile tissue were in fine fettle, and I was able to measure a couple of cycles, which were both about 3 hours in length.
Give it a try yourself. The obvious weaknesses with the way we were doing it is that the observations are personal and subjective, unlike those done with gadgetry that directly measures airflow, and since we were only doing a check every half hour our results were pretty chunky. The interesting thing about it, though, is that this is a rhythm our bodies express throughout your life, and most of us never even notice. It makes one wonder what other sneaky little patterns your organs are doing without your permission or control.
Kahana-Zweig R, Geva-Sagiv M, Weissbrod A, Secundo L, Soroker N, Sobel N. (2016) Measuring and Characterizing the Human Nasal Cycle. PLoS One 11(10):e0162918