Do you have breathing problems? If not, it's probably because you're constantly sighing throughout the day.
California scientists determined sighing is a vital reflex in maintaining breathing ability.
Within the lungs are about 500 million alveoli, which are small, balloon-like pockets that control the flow of oxygen and carbon dioxide throughout the lungs, according to The Washington Post.
Alveoli sometimes collapse, and if that happens a lot, one's breathing can become significantly impaired.
Sighing re-inflates collapsed alveoli by taking in twice the amount of air as a normal breath.
Study co-author and University of California, Los Angeles Professor Jack Feldman said,
Scientists initially became aware of the importance of sighing by observing patients of the first iron lung devices, which are ventilators that allow people to breathe if they have lost the physical capacity to do so on their own.
The earliest of such devices did not provide patients with regular, extra-deep breaths, resulting in death.
Iron lung devices available today account for this previous mistake.
The researchers also conducted an experiment on mice to learn how the act of sighing is regulated within the brain, according to ScienceAlert.
Lab mice sigh up to 40 times an hour and reportedly possess neurological systems very similar to those of humans.
In a statement, study coauthor Mark Krasnow of Stanford University said,
The researchers found increasing the presence of a certain type of neuropeptides, or molecules neurons use to communicate with each other, increased the animals' rate of sighing to 400 times an hour.
If they blocked the same types of neuropeptides, the mice stopped sighing altogether.
The key to helping patients with impaired breathing may be drugs that target these neuropeptides.
Feldman couldn't give a definitive answer, however, as to why people sigh in emotional distress.
This study was originally published in Nature.
Citations: Scientists uncover the brain mechanism that makes you sigh (The Washington Post), Sighing is actually a life-saving reflex, and scientists have found the switch that controls it (Science Alert), A sigh's not just a sigh - it's a fundamental life-sustaining reflex (The Guardian), UCLA and Stanford researchers pinpoint origin of sighing reflex in the brain (UCLA Newsroom)