Department of
Otorhinolaryngology, Bozyaka Teaching
and
Research Hospital,
Karabagùlar, Izmir, Turkey
Abstract
As a dark and not fully understood side of
human nature, yawning is believed to be a signs
of various physiological or pathological
behaviors of human. In this study, we aimed to
investigate the importance of yawning in the
evaluation of sleepiness. One hundred and
twenty-nine snorers who were suspected to have
obstructive sleep apnea syndrome underwent
polysomnography and were asked to fill the
Epworth sleepiness scale. The number of yawnings
of patients was counted during the day following
polysomnography. Patients were stratified into
two groups: those have apnea hypopnea index
<5 (n = 43, group 1) and those have apnea
hypopnea index >30 (n = 86, group 2). Mean
duration of sleep phases, oxygen saturations,
sleep efficacies, yawning frequencies and
Epworth scores of the groups were compared.
Correlations of yawning frequency with Epworth
scores, duration of sleep phases and mean oxygen
saturations were investigated. Sleep efficacies
were similar between the groups (p > 0.05).
Yawning frequencies in group 1 and group 2 were
43.48 and 75.76 (mean rank), respectively (p
< 0.01). Mean N1, N2, N3 phase durations and
oxygen saturations were significantly lower in
group 2 (p < 0.01). While there was a
negative correlation between yawning frequency
and duration of the non-REM phases and mean
oxygen saturation (r = -0.53 and r = -0.31,
respectively, p < 0.05), yawning frequency
was positively correlated with Epworth scores (r
= 0.46, p < 0.05). In addition to the
shortened phases of sleep, increased Epworth
score and decreased oxygen saturation, increased
yawning frequency may indicate sleep
deprivation.
Résumé
En tant que facette obscure et mal comprise
de la nature humaine, le bâillement est
considéré comme un signe de divers
comportements physiologiques ou pathologiques de
l'homme. Dans cette étude, nous avons
cherché à étudier
l'importance du bâillement dans
l'évaluation de la somnolence. Cent
vingt-neuf ronfleurs soupçonnés
d'être atteints du syndrome d'apnée
obstructive du sommeil ont subi une
polysomnographie et ont été
invités à remplir l'échelle
de somnolence d'Epworth. Le nombre de
bâillements des patients a
été compté pendant la
journée suivant la polysomnographie. Les
patients ont été stratifiés
en deux groupes : ceux ayant un indice
d'apnée hypopnée <5 (n = 43,
groupe 1) et ceux ayant un indice d'apnée
hypopnée >30 (n = 86, groupe 2). La
durée moyenne des phases de sommeil, les
saturations en oxygène,
l'efficacité du sommeil, la
fréquence des bâillements et les
scores d'Epworth des groupes ont
été comparés. Les
corrélations entre la fréquence
des bâillements et les scores d'Epworth,
la durée des phases de sommeil et les
saturations moyennes en oxygène ont
été étudiées. Les
efficacités de sommeil étaient
similaires entre les groupes (p > 0,05).
La fréquence des bâillements
dans le groupe 1 et le groupe 2 était de
43,48 et 75,76 (rang moyen), respectivement (p
< 0,01). Les durées moyennes des
phases N1, N2, N3 et les saturations en
oxygène étaient significativement
plus faibles dans le groupe 2 (p < 0,01).
Alors qu'il existait une corrélation
négative entre la fréquence des
bâillements et la durée des phases
non-REM et la saturation moyenne en
oxygène (r = -0,53 et r = -0,31,
respectivement, p < 0,05), la
fréquence des bâillements
était positivement corrélée
aux scores d'Epworth (r = 0,46, p < 0,05).
Introduction
Obstructive sleep apnea (OSA) syndrome is
characterized by deprivation of sleep quality
due to the repetitive collapse of the pharyngeal
airway and numerous arousals to resume
ventilation [1]. Although sleep-related
events such as apnea, hypopnea, arousal, reduced
oxygen saturation and altered sympathetic system
activity are the basic aspects of this syndrome,
various consequences of these sleep events such
as excessive daytime sleepiness (EDS), social
problems, increased likelihood of traffic and
occupational accidents, increased cardiovascular
events and stroke incidence may occur in the
short or long term [2&endash;4]. Among
these symptoms, signs and complications, EDS
seems to be associated with some of the
unfavorable results of OSA, such as increased
risk of motor vehicle accidents, work-related
accidents, cognitive and psychosocial
problems.
With the increased awareness of clinicians
and people about the importance and possible
complications of OSA syndrome, numerous studies
have been published regarding different aspects
of this disease [5, 6]. A variety of
objective and subjective test batteries have
been developed for the accurate evaluation of
OSA-related EDS. The most commonly used
objective and subjective tests are multiple
sleep latency test (MSLT), maintenance of
wakefulness test (MWT), OSLER (Oxford SLEep
Resistance) test and Epworth sleepiness scale
(ESS). Since objective methods are complex,
expensive and time consuming, ESS is the most
frequently used simple, inexpensive,
self-administered questionnaire that evaluates
and rates EDS in sleep disorders
[7].
Yawning is an easily observable and
quantifiable physiological phenomenon, which is
believed to be associated with a feeling of
comfort [8]. Although this familiar act
is a routine part of humans' daily life, it is
no more than 40 years that yawning has been a
matter of investigation with advances in
neuropharmacology. Yawning is a sophisticated
ritual that comprises inspiration phase at the
beginning, an acme period characterized with the
extensive contraction of the mimic muscles
together with a momentary interruption of
breathing and a final expiration phase, which
involves the relaxation of all participating
muscles. Various physiological and pathological
associations have been proposed with yawning in
recent years [9]. While various topics
such as ''arousal, brain cooling, social
empathy, ear pressure and brain hypoxia'' have
been associated with its physiological aspect,
numerous pathological conditions such as
''migraine, depression, Parkinson's disease,
renal insufficiency, gastro-esophageal reflux''
have also been associated with the occurrence of
altered quantity and quality of yawning
[10]. Although there is a common belief
regarding the association between yawning and
sleepiness among people from different cultures,
there are few studies which investigate this
association in the medical literature. At this
point, we aimed to investigate the importance of
yawning in the evaluation of EDS.
Discussion
EDS, which is one of the most frequent and
troublesome complaints of OSA syndrome, is
associated with various unfavorable consequences
of this disease such as increased likelihood of
traffic accidents, interpersonal problems and
reduced productivity [12]. EDS is also
reported to reduce quality of life (QOL) in OSA
patients [13]. Although the exact
molecular mechanisms and factors underlying EDS
are not well understood, investigators have
ascribed the presence of EDS to nocturnal
hypoxemia or sleep fragmentation or both
[14, 15]. In OSA patients, increased
circulating levels of tumor necrosis factor-a
(TNF-a), which results from hypoxia-induced
central nervous system inflammation, might play
a role in the emerging of sleepiness
[16]. Our findings are in agreement with
the knowledge that reduced oxygen saturations
during apneic episodes might induce
hypoxia-related neuronal inflammation in OSA
patients, and thus EDS may occur due to the
hypoxia-related neuronal damages. Additionally,
our findings suggest that decreased oxygen
saturation seems to be related with increased
sleepiness and YF in OSA patients. Similar to
our findings, Schiller stated in his study that
yawning was associated with decreased SaO2 and
increased carbon dioxide (CO2) concentrations in
the human central nervous system
[17].
In our study, we showed that yawning
frequency is negatively correlated with SaO2 and
positively correlated with excessive daytime
sleepiness and this correlations are consistent
with previous findings. In OSA patients, as
hypoxia induced central nervous system
alterations, sleep fragmentations may lead to
sleepiness [18, 19]. Several reports
stated that each arousal and each fragmentation
results in increased EDS. Previously, Roure et
al., stated that sleep apnea and sleep
disruption were not the primary determinants of
EDS in all OSA patients [20]; however,
since AHI is correlated with the ESS score we
may suggest that as a patient has more
apnea/hypopnea during sleep, it is possible for
the patient to experience much more excessive
daytime sleepiness. Moreover, since the sleep
efficacies of our groups were similar, it is
possible to suggest that EDS might be related to
other factors than sleep efficacy, such as
''decreased SaO2, shortened N3 phases of sleep
and increased AHI''. Concerning about the
duration of sleep phases and its relation with
excessive daytime sleepiness, it is not
impossible to ascribe EDS to shortened N3 phase
of sleep according to our findings. While the
duration of REM phase of sleep is similar
between the groups in our study, significant
shortening of the non-REM phases, ''especially
the most restorative N3 phase'', might be
associated with increased ESS scores and
eventually increased yawning frequencies.
Studies that investigated biorhythm of yawning
have stated that yawning has certain
characteristics, which reflects its complicated
nature. For example, yawning peaks in the
beginning of the morning immediately after
awaking. Another peak occurs in the late
afternoon and finally it reaches its maximum
level late in the evening, especially close to
bedtime [21].
Similar to these observations, our findings
indicate another physiological aspect of this
mysterious bio-act. In other words, yawning
seems to have a close interaction with diurnal
rhythm of the human nature and also with other
biologic necessities as sleeping. A previous
study, which investigated the association of
yawning with the transition between periods of
high level activity and low level activity or
arousal, stated that yawning was surely only one
means of regulating arousal and activity; it may
well be a marker of altered level of arousal,
rather than a cause [21]. In the light
of our findings and other observations, it is
possible to associate yawning with sleep.
Studies evaluated human adults, provided
evidence that yawning occurs approximately
7&endash;8 times a day [21]. An average
yawning frequency of our groups was 4&endash;5
and 10&endash;11 per day for groups 1 and 2,
respectively. Discrepancy of these average
scores might be related to various ''not
well-known'' characteristics of the act of
yawning. It is obvious that we need more studies
regarding the dark sides of yawning in human. In
the light of our results, we may conclude that
similar to the shortened N3 phase of sleep,
increased Epworth scores and decreased oxygen
saturations, increased frequency of yawning may
indicate sleep deprivation as well. Our findings
revealed that daily frequency of yawning seems
related to the degree of EDS of a patient.
Physicians who involved with obstructive sleep
apnea may adapt ''yawning'' to their clinical
practice in order to predict the sleepiness of
their patient.
