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 mise à jour du
13 mars 2002
1974, may 2, p1028
1974, june 20, p1439
Why the yawn
Siegal S, Twiest M, Friedell A, Bhangoo K
Why do people yawn ?


Sheppard Siegal, New York

The purpose of yawning remains a mystery. Physiology textbooks barely mention its existence; none explain its function. Surely, it cannot have purposelessly survived the evolutionary process. Its elucidation must square with its constant manifestations: jaws strikingly agape; prolonged deep inspirations; association with boredom, drowsiness and sleep; and extrerne suggestibility.

"Why is it, asked my wife" that when I yawn I can detect the odor of gas more readily than otlherwise? Each time I check, the pilot light's out." Perhaps the usefulness of yawning has to do with the sense of smell rather than with breathing? A large bolus of air is placed in contact with a maximally exposed nasopharynx, Its markedly increased extent has been demonstrated on x-ray examination. Yawning rnight be a special method of sampling the circumambient air for possibly harmful osmules.

Besides providing "flavor and the spice of life" smell possesses considerable survival value. No sensible animal will cat anything unless it is first check-ed out by olfactory rneans. As an allergist, I am particularly aware that prolonged anosmia exposes its victims to unsuspected dangers.

The yawn's protection would be most needed at a moment of vulnerability: as one is about to sleep or when one comes awake. Whether to smell escaping gas, or in the primitive wild to be alerted to a nearby predator, yawing may enhance this vital fonction. As for suggestibility, protective sampling would be improved by group participation. Perhaps readers may suggest other solutions to the elusive enigma: why is a yawn ? 

Melvin Twiest, University Hospital, Ann Arbor, Mich

Dr Siegal's query and intriguing hvpothesis about the purpose of yawnig prompted me to search several physiology textbooks for a satisfactory answer. Having falied to find one, I should like to offer a possible alternative explanation.

A common and important problem of postoperative patients is inadequate pulmonary expansion, causing alveolar collapse and areas of atelectasis to be on chest x-ray study. The patients become mildly febrile, and if the problem is not corrected. pneumonitis often ensues. The basic treatment consists of clearing of excess secretions, if present, and of forced, periodic lhyperventilation (deep breathirig, intermittent positive-pressure breathing, blowing into a tube against pressure, etc.) to help inflate the collapsed segments. During ventilation with modern volunie-type respirators, a periodic "sigh" is given during ilie ventilatory cycle. Yawning usually occurs during periods of relative hypoventilation, as docs sighing. One rarely does either during vigorous activity - such as a tennis match, or, for most of us sexual intercourse. I agree with Dr. Siegal that yawning is a protective response, but that possibly a more logical reason for its existence is to protect against the consequences of alveolar collapse, which may occur during periods of relatively inadequate ventilation.

Aaron Friedell, Minneapolis, Minnesota

A brief reply tu "Why the Yawn ?" A yawn is a healthful and valuable maneuver. Ashley Montagu stated, "A yawn is a long inhalation with the mouth wide open followed by a slow exhalation, Breathing is both through the mouth and nose," (JAMA, 290: 127- 128, 1962). As Montagu notes, a yawn and a lengthened inhalation contribute several mechanical, physiologic and biochemical effects: "A temporay increase of tension by its massive inspiration of oxygen and exhalation of CO2 serves to restore the depleted oxygen content of the blood. Virtually all cephalic structures are in consequence stimulated."

The atmospheric air and partial oxygen pressure are guided by a yawn more directly into the terminal bronchioles and alveoli (the micro ventilation and circulation). The increase into the terminal areas of the lungs will cause an increased stretching of the bronchial musculature and the terminal vagus (parasympathetic) nerve endings. That would stimulate production of acetylcholine to relax terminal arterioles and lower resistance of the circulation. The yawn - a valuable health maneuver.

Kulvant S Bhangoo, Mercy Hospital Buffalo, NY

The strectching of limbs is also constant manifestation of the act of yawning in addition to "jaws strikingly agape, prolonged deep inspirations..." mentioned by dr Siegal. An interesting explanation of the movements has been postulated by Last. The lateral pterygoids and the soleus muscles contain, within their substance, rich venous plexuses that empty with the contraction of theses muscles and, on this account, have been appropriately called "peripheral hearts". The prolonged and forceful contraction of the lateral pteroigoids in opening the jaws wide and the stretching of limbs during the yawn, squeeze blood from the plexuses, enhancing venous return. The contraction of the diaphragm during the concurrent deep inspiration further aids the venous return from the abdomen. This effect would explain all the movements associated with yawning and further suggest that is probably precipatted by peripheral venous stagnation. It does not, however, explain why ywans are "catching".
voir aussi
Baenninger R, Binkley S, Baenninger M Field observations of yawning and activity in humans.
Baenninger R On yawning and its functions
Baenninger R, Greco M Some antecedents and consequences of yawning
Greco M, Baenninger R On the context of yawning: when, where, and why ?
Baenninger R Some comparative aspects of yawning in Betta sleepnes, Homo Sapiens, Pantera leo and Papio sphinx