So in times of stress, when breathing is less variable, a sigh can reset the respiratory system and loosen the lung's air sacs, or alveoli, which may be accompanied by a sensation of relief, Vlemincx said.
Knowing this, it would seem logical then to add some sighs to the breathing regimes of people on mechanical, ventilators. As it turns out, it has been tried.
"If you put in a few sigh breaths, people feel better," said Frank Wilhelm a clinical psychologist at the Universität Basel in Switzerland.
Wilhelm has studied the role of breathing in psychological disorders extensively.
On the other hand, too much sighing can add too much noise to the system and can also throw the system out of whack. This appears to be what happens to people experiencing panic attacks, said Wilhelm.
"Panic victims don't recover from sighing," said Wilhelm.
In fact, people experiencing panic attacks have been long observed to involve a great deal of sighing, and show all the symptoms of hyperventilation: dizziness, numbness in the extremities, etc., he said.