The physiological sigh involves two inhales through the nose followed by a long, slow exhale through the mouth until lungs are empty.

“The physiological sigh consists of, as many of you know, two inhales through the nose, followed by a long, until lungs empty, exhale through the mouth. Typically, the first inhale is longer. Again, it's done through the nose. The second inhale is shorter, kind of a sharp inhale to make sure you maximally inflate all of the little sacs within your lungs. And then the exhale is a long, slow exhale that dumps all of your air.”