Sleep Posters presented on Wednesday,
October 24, 2012
PURPOSE: It has been suggested that
sleep apnea may have an adaptive benefit, the
reduction of nocturnal respiratory heat loss. On
the other hand, there is a growing body of
evidence that yawning may be a thermoregulatory
mechanism that represents an adaptation to
conditions that increase body/brain temperature,
such as sleep fragmentation. Since sleep apnea
and yawning are thermoregulatory mechanisms
functioning towards opposite directions, we
hypothesized that excessive daytime sleepiness
due to sleep apnea is not characterized by
excessive yawning.
METHODS: We have studied 85
consecutive subjects with excessive daytime
hypersomnolence (Epworth scale³12) who underwent
a full night diagnostic polysomnography (PSG).
Patients were classified as sleep apneic when
their Apnea-Hypopnea Index (AHI) was ³15
events/hour and as non-sleep apneic when their
AHI was < 5 events/hour. Before PSG, all
patients were asked whether they usually
experience bouts of yawning from morning
awakening until early evening (6 pm) after an
efficient night sleep (>6 hours).
RESULTS: We discarded 12 subjects
with AHI 5-14 events/hour. Fifty two subjects
with hypersomnolence were diagnosed to suffer
from sleep apnea syndrome (age 47±13 yo;
Epworth scale 16±3; AHI 51±22), while
the remaining 21 sleepy subjects had no sleep
apnea (age 44±17; Epworth scale 17±3;
AHI 2±1). Bouts of yawning have been
reported by only 9 out of the 52 (17%) sleepy
apneic patients and by 18 out of the 21 (86%,
p<0.001) sleepy nonapneic patients.
CONCLUSIONS: It seems that absence of
yawning bouts in a sleepy patient may predict
the presence of sleep apnea syndrome as a cause
of the excessive daytime sleepiness with a
sensitivity of 83% and a specificity of 86%. The
reason is unclear, however, it can be speculated
that sleep apnea and yawning, both sharing an
adaptive thermoregulatory ability towards
opposite directions (heating/cooling
respectively), usually do not coexist.
CLINICAL IMPLICATIONS: Our data
suggest that questioning about daytime excessive
bouts of yawning should be included in the
recording of symptoms when taking medical
history from sleepy subjects in the Sleep
Clinic.
