Journal of Clinical Sleep Medicine, Vol. 2, No. 2, 2006
duration.1 This definition provides guidance for the lower limit
with which to define an arousal, but no rules are provided with
regard to the upper limit, that is, how long an arousal may last.
Using standard Rechtschaffen and Kales2 scoring rules, a period
of arousal occupying more than 50% of an epoch would be scored
as Wake. Therefore, periods of arousal lasting greater than 15 sec-
onds could tend to be included in wake after sleep onset (WASO)
time and might not be counted as distinct arousals.
We have previously reported3 on the prevalence of both brief
(3- to 15-second) and long (≥ 15-second) arousals in 50 patients
(32 men, 18 women) with obstructive sleep apnea (OSA), noting
that 22% of all arousals and 37% of arousal time was attributable
to these longer arousals. Even with the limited number of indi-
viduals included in our original report, evidence for a potential
relationship between the longer arousals and the Epworth Sleepi-
ness Scale (ESS) score4 was identified, though it failed to reach
clinical significance (p = .06).
This paper expands on our previous findings, with this report
tandard practice parameters define electroencephalographic
(EEG) arousals as waveform changes of at least 3 seconds in
correlating the subjective estimate of sleepiness as defined by the
ESS, with the presence of brief and long arousals in full-night
polysomnograms (PSG) for 100 individuals.
Patients referred for evaluation of OSA who completed a full-
night PSG evaluation without intervention (without continuous
positive airway pressure or supplemental oxygen) were eligible
for this study. Each had been interviewed and examined by a
sleep medicine physician and found to meet criteria for the in-
dications for PSG.5 Patients were excluded if the study failed to
have a minimum of 4 hours of sleep, if periodic limb movement
(PLM)-associated arousals were identified at a rate that exceeded
4 per hour, or if alpha intrusion made delineation of arousals im-
practicable. This report details the findings from 100 consecu-
tive individuals referred to our center who met these criteria. This
study protocol was reviewed and approved by the Research Eth-
ics Review Board of University Community Hospital.
A standard PSG in our lab uses the following protocol: after
the patient is acclimated to the facility, they are fitted with EEG
(C3/A2, C4/A1, O2/A1, O1/A2), electrooculographic (ROC/A1,
LOC/A2), and chin electromyographic (EMG) electrodes for
sleep staging, according to the criteria outlined by Rechtschaffen
and Kales.2 Electrodes are placed on both legs, as described in
American Sleep Disorders Association (ASDA) Atlas Task Force
Report,6 to monitor myoclonic activity. Uncalibrated inductive
On the Potential Clinical Relevance of the Length of Arousals From Sleep in
Patients With Obstructive Sleep Apnea
Daniel J. Schwartz, M.D.1,2; Pat Moxley, R.P.S.G.T.1
The Tampa Sleep Center, University Community Hospital, and Department of Medicine, University of South Florida, Tampa, FL
This was not an industry supported study. Drs. Schwartz and Moxley
have indicated no financial conflicts of interest.
Submitted for publication October 6, 2005
Accepted for publication November 21, 2005
Address correspondence to: Daniel J. Schwartz M.D., The Tampa Sleep Cen-
ter, 3100 East Fletcher Avenue, Tampa, FL 33613; Tel: (813) 615-1544; Fax:
(813) 615-0878; E-mail: email@example.com
Study Objectives: To assess, in individuals referred for evaluation of
obstructive sleep apnea, the potential clinical significance of brief versus
longer arousals from sleep.
Methods: Full-night polysomnographic tracings from 100 patients re-
ferred for evaluation of obstructive sleep apnea were analyzed to delin-
eate the duration of each arousal event. These data were then correlated
to the patient’s subjective perception of sleepiness as estimated by the
Epworth Sleepiness Scale (ESS).
Results: A significant relationship (p < .0001, r2 = .167) was noted be-
tween the frequency of the longer arousals (≥ 15 seconds) and the ESS.
This relationship was significant, but distinctly weaker (p = .004, r2 =
.073), with the shorter arousals (3-15 seconds); moreover, the associa-
tion with the brief arousals failed to remain significant (p = .678) after
controlling for the effect of the longer arousals.
Conclusions: Individuals with obstructive sleep apnea experience fre-
quent respiratory event associated cortical arousals, many of which are
greater than 15 seconds in duration. These longer arousals, which, in
this study, constituted 18.4% of all arousals and accounted for 37.5% of
the total arousal time, correlate more closely with the ESS than does the
frequency or time attributable to the more numerous brief arousals. This
suggests that these more-prolonged arousal events may have a greater
impact on the restorative aspect of sleep, or on the perception thereof.
Keywords: Arousals from sleep, obstructive sleep apnea, sleepiness
Citation: Schwartz DJ; Moxley P. On the potential clinical relevance of
the length of arousals from sleep in patients with obstructive sleep ap-
nea. J Clin Sleep Med 2006;2(2):175-180.
Journal of Clinical Sleep Medicine, Vol. 2, No. 2, 2006
ignores Wake time, which might otherwise be included in WASO
using a more-standard definition of sleep onset (3 consecutive ep-
ochs of stage 1 or the first epoch of any other stage of sleep).20
Using this more-standard paradigm, we determined WASO for
our cohort (men = 58.6 ± 43.9, women = 64.8 ± 42.0, p = .473).
WASO determined using our study paradigm (eliminating any
WASO during which an arousal was counted) resulted in similar
data (men = 44.8 ± 41.0 minutes, women = 54.0 ± 42.0 minutes, p
= .271). Thus, as has been noted by Resta et al,19 the women had a
slightly larger amount of WASO than did the men, but the differ-
ence in our cohort did not reach statistical significance.
Shepertycky et al21 have also commented upon sex differences
in OSA, with their study identifying differences in the clinical
presentation of OSA between men and women, noting that wom-
en more commonly express symptoms of insomnia or depression
than do men.
Thus, though others have identified potential sex differences in
various parameters related to the OSA, to the best of our knowl-
edge, no one has ever reported on a specific sex difference as
pertains to the relationship of these symptoms and the length of
cortical arousals associated with respiratory events.
Our study demonstrates that the most significant relationship
between the subjective symptoms expressed in the ESS is with
the long arousals occurring in Stages 1 and 2 sleep. This was con-
sistent for both men and women. Whether a sex difference will
be identified for other parameters (as suggested for the events in
REM sleep) will require further study, but we would stress that,
for both men and women, by far the most significant associa-
tion with the ESS was with the longer arousals in Stages 1 and 2
Our data would tend to support the sleep-continuity theory, with
the finding that the effect of sleep fragmentation on subsequent
perceived daytime sleepiness was associated more closely with
the duration of the interruption than with the frequency thereof.
We would be remiss not to note that the ESS is perhaps a rather
crude subjective assessment of sleepiness, and, though our data
would suggest a rather remarkable association between this sub-
jective scale and the longer arousals that disrupt sleep in indi-
viduals with OSA, further work is required to determine whether
a relationship will be identified with other measures of daytime
performance or objectively tested levels of sleepiness.
In summary, though there may be many unanswered questions
generated by the findings of this study, the significant relationship
between the long arousals and the subjective estimate of sleepi-
ness appears fairly strong and should, perhaps, influence how we
look at our PSG data in the future. We would propose that simply
counting the number of arousal events that occur may be inad-
equate and that some assessment of the length of the arousals may
need to be included in our analyses.
The authors would like to acknowledge the assistance of Mr.
Mike Longman who created the report software package used to
collate the data for this study.
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DJ Schwartz and P Moxley