About the Sighs of It

What’s in a Yawn or a Sigh? Are we bored or restless or yearning for something different, exciting, new? Though it’s widely assumed that sighing signifies ennui and yawning shows disinterest, there are provocative physiologic bases for both. A unifying factor in these breathing patterns seems to be an effort to get more air (i.e. oxygen) into the lungs; the brain prompts the body to respond automatically–as a reflex in fact.

Pulmonologists have recognized the value of sighing in respirator patients for years. When oxygenation is marginal, adding a deep Sigh to ventilator settings at appropriate intervals can give a real boost to blood oxygen levels. There’s both a biochemical and an ‘automatic’ component to Sighing respirations. For example, in diabetic ketoacidosis when the blood sugar levels skyrocket and organic acids are raging, deep sighing respirations are one method the body uses to try to correct the imbalance. Sighing is the most important arousal mechanism during sleep. It is known that babies who die from SIDS (Sudden Infant Death Syndrome) have significantly decreased numbers of sighs during sleep. Additionally, when an adult is dying and unconscious, a pattern of sighing respirations often takes over. Again, the acid-base balance and levels of both oxygen and carbon dioxide are important in regulating the breathing pattern.

While scientists do not understand all the mechanisms of yawning, there is agreement that it, too, is an involuntary respiratory reflex which regulates the carbon dioxide and oxygen levels in the blood. The mechanics of a yawn involve a wide, reflex opening of the mouth followed by a deep inhalation and a slow exhalation of oxygen. At times of fatigue or boredom, we often have shallow breathing which generates a decrease in blood oxygen concentrations. A yawn in these circumstances causes a sudden increase in oxygen levels with associated increased alertness, increased heart rate and a decrease in the build up of carbon dioxide–all aspects stimulatory in character. In case I’m boring you with all this medical jargon. . .read on.

One provocative theory contends that the mechanics of a yawn actually serve to “clean the brain” by accelerating the normal cerebrospinal fluid movement and absorption process. All the pressures generated by pulling on neck muscles, the skull, and the brain itself can facilitate the spinal fluid movement. Although we produce about a pint of spinal fluid every day, we only have the capacity to hold about one fourth of this quantity–so there are obvious advantages to enhancing the normal circulation.

Interestingly, people with brain tumors often yawn excessively while schizophrenics yawn very little. Using the above explanation, the increased spinal fluid pressures generated in brain tumor patients may necessitate more yawning in an effort to decrease this pressure. Alternately, schizophrenics have larger than average ventricular spaces in their brains and an excess of neurotransmitters as well. If in fact they could voluntarily yawn more often, it’s conceivable that the increased spinal fluid circulation generated might help to decrease symptoms. It’s an interesting concept!

Is yawning “contagious”? It certainly seems so, when one person’s yawn predictably triggers others in nearby folks. One explanation is that everybody in the room needs more oxygen at the same time. Sounds plausible at first, but people trigger yawns in folks in other cars heading into work and also in people attending outdoor functions. In both instances, oxygen exposures should not be the explanation. Perhaps it’s a primal remnant–a symbolic baring of teeth, or simply the power of suggestion. However, I read one article that stated if you really dislike a person who yawns in your presence, you will not yawn back. Check it out the next time you find yourself in such a situation! Overall, there is no consensus on the etiology of consensual yawning.

I’ll conclude with a few other tidbits I found interesting. Fetuses yawn in utero, but they clearly have no oxygen circulation in their lungs. Why? While people do yawn throughout the day, people yawn most within the first hour of awakening each day. The neurochemistry of yawning has been studied and is both complex and fascinating. For instance, there’s an interesting association in male animals (including men) between yawning and penile erection; clearly boredom is not the explanation here!

Hopefully, you’ve been stimulated by this potentially boring topic. And there’s still much to be learned. Actually, a yawning chasm exists in our information on the subject. But remember it is known that, “A healthy male adult bore consumes each year one and a half times his own weight in other people’s patience.John Updike

Stephen L. Hines, M.D.
November 2000