Sighing is not just a human emotional response, but a reflex essential to the workings of the lungs. Researchers say the findings may lead to new treatments to help people who sigh too much or not enough.
Your life depends on your ability to sigh.
Yes, we sigh when we’re exhausted or stressed — and when the weight of the world feels like too much to bear — but it turns out that sighing is also an essential life-sustaining reflex that is necessary to keep our lungs from collapsing.
This week researchers from the University of California, Los Angeles, and Stanford University described the neural circuitry of sighing for the first time as well as pinpoint the exact location in the brain from which our sighs originate.
The study, published Monday in Nature, could lead to treatments for people who don’t sigh enough, or those who sigh too much, the scientists said. It could also offer clues to how sighs might be triggered by emotional states.
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Chances are you sigh much more than you realize. Most humans heave an involuntary sigh an average of 12 times an hour, said Jack Feldman, a professor of neurobiology at UCLA and a senior author on the paper.
You can test this for yourself by lying down in a quiet room and paying close attention to your breathing. About once every five minutes you will notice that your body takes an inhalation, and just before the exhale, adds another inhalation on top of it.
These types of sighs are not related to emotion, Feldman said. Instead, they provide an extra gust of air that helps to reinflate some of the 500 million tiny balloon-like sacs in our lungs called alveoli.
The alveoli are the sites where oxygen enters the bloodstream and carbon dioxide is removed. Although each individual sac is just 2/10th of a millimeter in diameter, together they have the surface area of a tennis court.
When they collapse, the only way to pop them open again is to sigh, which brings in twice the volume of a normal breath, Feldman said.
And we’re not the only animals who sigh regularly. Rodents are even more frequent sighers than humans, taking a double inhale up to 40 times an hour.
The discovery of how the brain turns a normal breath into a sigh originated from two separate lines of inquiry from Feldman’s lab at UCLA and biochemist Mark Krasnow’s lab at Stanford.
Some years ago, a toxin found on the skin of South American frogs was found to induce rapid sighing when injected into brainstems of rats. Later, two small populations of neurons that produce similar molecules were found near a region of the brain well known as the core of the body’s breathing control center.
The new work could help scientists develop drugs that can induce sighing in people who don’t naturally sigh enough, or to inhibit sighs in those who suffer anxiety and other disorders that can lead to too much sighing.