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
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