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Scoring Center: Polysomnographic Features of Sleep
Disordered Breathing - UARS AND RERA By Nic Butkov, RPSGT
T
he preceding two articles in this series discussed the basic
concepts of evaluating respiratory data within the context of sleep-wake physiology.1 This article continues with an
exploration of other sleep disordered breathing (SDB) variants
and a discussion regarding newly emerging event definitions.
Upper Airway Resistance Syndrome
The upper airway resistance syndrome (UARS) was described in 1993 by Christian Guilleminault and coworkers
at Stanford University.2 The polysomnographic features of
UARS include repetitive increases in respiratory effort with
consequent EEG arousals, but without airway collapse, oxygen
desaturation or hypoventilation.
UARS is distinguished from the obstructive sleep apneahypopnea syndrome (OSAHS) by an apnea and hypopnea
index (AHI) of less than 5 events per hour and by lack of O2
desaturation.3 Guilleminault describes three possible patterns
of UARS based on esophageal pressure measurements (Pes):
 Pes Crescendo is a progressive, breath-by-breath increase
in Pes, terminating in an EEG arousal or activation.
 Sustained continuous effort is a more stable, yet persistent
increase in Pes over a period of several epochs, terminat
ing in an EEG arousal.
 Pes reversal is an abrupt drop in Pes following a sequence
of variable respiratory effort, independent of EEG arousal.
The clinical symptoms of patients with UARS differ from
those with OSAHS. In contrast to the latter, patients with
UARS frequently complain of insomnia instead of hypersomnia, and are more likely to present with symptoms of
fatigue rather than sleepiness. Patients with UARS are usually
non-obese and are often hypotensive instead of hypertensive.
Patients with UARS typically have particular craniofacial features, including a high and narrow hard palate and abnormal
overbite. Other symptoms related to UARS include postural
hypotension, cold hands and feet, history of fainting, anxiety,
and complaints of fibromyalgia and chronic fatigue.4
At the present time, the classification of UARS as a distinct
syndrome separate from OSAHS remains controversial; however, the constellation of symptoms associated with the polysomnographic features of UARS has been well-documented.
Nic Butkov, RPSGT
Nic Butkov, RPSGT, has been in the sleep
field since 1984 and is Education Coordinator at Rogue Valley Sleep Center and
Director of the School of Clinical Polysomnography in Medford, Ore.
Respiratory Effort-Related Arousals
The term respiratory effort-related arousal (RERA) was introduced by the American Academy of Sleep Medicine (AASM)
in 1999, defined as “a sequence of breaths characterized by
increasing respiratory effort leading to an arousal from sleep, but
which does not meet criteria for an apnea or hypopnea.”5 This
definition is similar to the Pes crescendo definition for UARS
as described above, and has been used interchangeably with
UARS scoring definitions; however, the scoring of RERAs alone
does not define UARS. RERAs are more commonly regarded
as part of the obstructive sleep apnea-hypopnea continuum, and
the threshold at which RERAs are distinguished from obstructive hypopneas is generally based on the most recent hypopnea
definition.
The new AASM scoring manual has redefined RERA as “a
sequence of breaths lasting at least 10 seconds characterized by
increasing respiratory effort or flattening of the nasal pressure
waveform leading to an arousal from sleep when the sequence of
breaths does not meet criteria for an apnea or hypopnea.”6
The AASM manual notes that esophageal pressure measurement is the preferred method of assessing changes in respiratory
effort, but allows for the use of nasal air pressure and inductance
plethysmography. This differs from the manual’s specification for
distinguishing obstructive hypopneas, which states: “Classification of a hypopnea as obstructive, central, or mixed should not
be performed without a quantitative assessment of ventilatory
effort (esophageal manometry, calibrated respiratory inductance
plethysmography, or diaphragmatic EMG).”
In actual practice, the only method that adequately provides a
quantitative measure of respiratory effort is esophageal manometry. Inductance plethysmography, whether calibrated or noncalibrated, is a surrogate measure of effort that is susceptible to
signal distortion caused by patient movement, postural changes,
and/or belt displacement. Diaphragmatic EMG cannot provide
quantitative ventilatory effort measures because it is a qualitative
signal. Without the use of esophageal manometry, RERAs are
usually recognized by relative changes in airflow and/or effort
preceding an arousal. Essentially, a RERA can be described as a
subtle form of obstructive hypopneas, without the requisite O2
desaturation (as currently defined by Medicare).
Paradoxical Respiratory Effort
Paradoxical respiratory effort refers to out-of-phase movements of the chest and abdomen during inspiration and expiration. This pattern is often regarded as indicative of upper airway
obstruction and used to help differentiate between obstructive
and central respiratory events.
However, paradoxical movements recorded by respiratory
belts are not always reliable indicators of airway obstruction.
Phase shifts recorded by the belt sensors may be seen in normal
individuals, especially during rapid eye movement (REM) sleep.
The extent to which paradoxical movement is recorded is also
dependent on the type of transducer used, the exact placement of
the belts, and the patient’s sleeping position and body habitus.
Phase shifts between the thoracic and abdominal respiratory
A2Zzz 18.4 | December 2009
25
Figure 1. Respiratory effort-related arousal (2-minute window). This sample demonstrates a respiratory effort-related arousal (RERA),
identified by progressive increase in negative esophageal pressures (Pes crescendo), coinciding with decrease in nasal airflow (flow limitation),
and terminating with an EEG arousal. By some definitions, this event could be scored as an obstructive hypopnea, except it does not meet the
requisite (Medicare) O2 desaturation criterion. Sample provided by Stanford Sleep Medicine Center in Redwood City, CA.
A2Zzz 18.4 | December 2009
 Continued on Page 26
Figure 2. Evidence of increased upper airway resistance (2-minute window). In this example, an EEG arousal is seen on the left side of the
display, associated with a preceding event. Following the arousal, a new cycle begins with increase in negative esophageal pressures (Pes
crescendo) and coinciding decrease in nasal airflow (flow limitation). However, the EEG activation (delta burst) seen at the end of this event does
not meet current AASM criteria for arousal. (The AASM scoring manual defines arousal as an abrupt shift in EEG frequency including alpha, theta
and/or frequencies above 16 Hz. The AASM definition does not include other forms of EEG activation, such as K-complex clusters or delta bursts.)
Since it is difficult to adequately discern EEG patterns in a compressed time scale, the effects of any perceived event on the EEG also should be
examined using a standard 30-second window display. Sample provided by Stanford Sleep Medicine Center in Redwood City, CA.
 Continued from Page 25
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channels are only useful when the signals clearly shift in a cyclical fashion from out-of-phase during the respiratory event, back
to in-phase during the recovery breaths.
Should RERAs Be Scored?
The most accurate method of measuring increased inspiratory effort is by esophageal pressure manometry. However, this
method is invasive and is not routinely used by most clinical
sleep centers. It has been suggested that nasal air pressure can
be used as a measure of flow limitation, whereby the presence of
increased airway resistance is represented by a flattening of the
nasal air signal waveform.
One problem with this approach is that minor changes in the
waveform shape can easily be over-scored. While nasal airflow
pressure detection is very sensitive to minor changes in airflow,
it is also susceptible to artifacts caused by cannula displacement
and mouth breathing. Thus, any perceived changes in the airflow
pattern must be carefully examined within the context of the
EEG to determine whether the changes are associated with
EEG arousal or activation.
Because of differences in sensor technology, filter configurations, and the manner in which the data are displayed, the airflow
flattening effect may vary in appearance. The low-frequency filter
should be set to a very low setting (preferably 0.05 Hz or less) to
detect the flattening effect. Signal integrity must be verified and
maintained by the attending technologist. In some instances, nasal airflow pressure detection may be counterproductive if signal
loss is a frequent occurrence.
The key feature of RERA is EEG arousal. Without the detection of arousal, changes in airflow shape alone are meaningless. Detection of EEG arousal or activation is contingent on
flawlessly recorded EEG signals that are adequately sampled
and displayed in an appropriate manner. It is also important to
recognize that commonly used criteria for EEG arousals do not
address other forms of EEG activation such as delta bursts or Kcomplex clusters. These are more often seen in younger patients
with UARS or OSAHS.
Because of the subjective nature of RERA recognition, it may
be suggested that the presence of suspected RERA patterns
should be described in written form rather than tabulated, unless
esophageal pressure measurements are recorded and correlated
with the EEG. A subjective assessment of the patterns can be
clinically relevant, but scoring each individual event could potentially lead to an overestimation of SDB severity. At the present
time, the scoring of RERAs does not meet most reimbursement
criteria for the treatment of SDB.
Clinical Versus Industry-Based Respiratory Event Definitions
Sleep technologists should be aware of a growing trend toward
industry-based respiratory event definitions, as used in home
sleep testing (HST) and positive airway pressure (PAP) compliance data collection. These definitions rely on proprietary
algorithms, with signals derived either from PAP flow/pressure
sensors (in the case of PAP data collection), or from a limited
number of respiratory parameters (in the case of HST devices).
The ongoing development of new technologies is essential for
the advancement of the field. However, sleep professionals are
cautioned against the indiscriminate adoption of industry-based
scoring definitions and diagnostic labels. Any claims pertaining to the diagnostic capabilities of these technologies should
be carefully assessed in terms of scientific evidence, professional
judgment and common sense.
For the most part, limited channel HST and PAP data collection systems are useful for detecting unambiguous obstructive
apnea. Advanced PAP sensor technology also may help discern
between closed and open airway apneas – an important distinction in making titration decisions. However, the main limitation
of these systems is lack of information regarding the patient’s
physiological state. The estimation of hypopneas, RERAs, flow
limitation, or other less obvious forms of SDB may be inaccurate
because of normal variants of sleep/wake physiology, movement
artifacts, mask leaks, mouth breathing, or sensor displacement.
Without having access to the neurophysiological aspects of sleep,
it is often difficult to assess the validity or the clinical significance of events tabulated by these devices.
Automated Event Scoring and Tabulation
Despite the many complexities and ambiguities associated with accurate SDB evaluation, software-based automated
scoring options are continually marketed to the sleep field. The
algorithms used for automated scoring are usually oversimplified and do not take into account normal variants of sleep/wake
physiology, artifacts, or SDB patterns that do not fit common
scoring criteria. In most instances, automated scoring functions
tend to overestimate respiratory events, leading to misdiagnoses
in patients whose symptoms may not even be related to sleep
disordered breathing.
Attempts have been made to validate automated scoring
functions by comparing visual and automated scores, but these
are typically conducted within the narrow boundaries of rulebased definitions that have been sufficiently simplified to yield
similar results by both methods. Using this approach, the scoring
process, whether visual or automated, becomes a perfunctory
exercise that is reproducible but does not necessarily reflect clinical reality.
A Practical Approach to Accurate SDB
Evaluation
As discussed in the previous articles, a meaningful interpretation of SDB relies on recognizing clinically significant respiratory phenomena relative to the patient’s physiological state.
Accurate event scoring relies on multiple factors, including the
quality of the recorded signals, the scorer’s ability to differentiate potentially detrimental events from normal variants of sleep/
wake physiology and from recording artifacts, and the implementation of pattern recognition skills relative to each individual
recording.
There are no simple scoring formulae that can encompass all
the different variants of SDB. The ability to rapidly assess and
accurately describe the nature and significance of any suspected
respiratory anomaly during sleep largely depends on scorer’s level
of experience. Sleep technologists are encouraged to continually
seek to improve their skills in this area, not by merely relying on
a “cookbook” scoring style, but by careful observation, ongoing practice, and by balancing existing scoring rules with sound
professional judgment.
A2Zzz 18.4 | December 2009
27
References:
1. Butkov N. Scoring center: polysomnographic features of
sleep disordered breathing. A2Zzz. 2009 June;18(2):25-27
and Sept;18(3):26-30.
2.
Guilleminault C, Stoohs R, Clerk A, Cetel M, Maistros P.
A cause of excessive daytime sleepiness: the upper airway
resistance syndrome. Chest. 1993 Sep;104(3):781-7.
3.
Guilleminault C, Bassiri A. Clinical features and
evaluation of obstructive sleep apnea-hypopnea syndrome
and upper airway resistance syndrome. In: Kryger M, Roth
T, Dement WC, editors. Principles and practice of sleep
medicine. 4th ed. Philadelphia: Elsevier Saunders;2005. p.
1043-1052.
4.
5.
6.
Guilleminault C, Chowdhuri S. Upper airway resistance
syndrome is a distinct syndrome. Am J Respir Crit Care
Med. 2000 May;161(5):1412-13.
American Academy of Sleep Medicine. Task Force
Report. Sleep-related breathing disorders in adults:
recommendations for syndrome definition and
measurement techniques in clinical research..Sleep. 1999
Aug 1;22(5):667-89.
The AAST acknowledges and thanks
the following organizations for their
generous support and for investing in
the future of the sleep technology
profession as
ResMed &
Respironics, Inc.
American
American Associatio
Associatio nn
Sleep TTechnologists
echnologists
of
of Sleep
AAST
2009
Cadwell
Laboratories, Inc.
American Associatio
Associatio nn
American
of Sleep
Sleep TT echnologists
echnologists
of
AAST
2009
American Associatio
Associatio nn
American
of Sleep
Sleep TT echnologists
echnologists
of
AAST
2009
AAST Supporter Members:
Cardinal Health &
MVAP Medical Supplies, Inc.
American Academy of Sleep Medicine. The AASM
manual for the scoring of sleep and associated events: rules,
terminology and technical specifications. Westchester, Ill:
American Academy of Sleep Medicine; 2007. 
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