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TECHNICAL CORNER: THE EVOLVING DEFINITION OF HYPOPNEA:
DESATURATIONS, AROUSALS, BOTH OR EITHER?
By Richard S. Rosenberg, PhD
It wasn’t that long ago that Medicare required 30 apneas
recorded during a sleep study to qualify a patient for treatment
with continuous positive airway pressure (CPAP). Twenty-nine
apneas were not enough, and hypopneas were not considered.
Consider the event in Figure 1. I refer to it as an event because
there is a clear change in breathing in the middle of this tracing.
There is a decrease in the amplitude of the nasal pressure signal
and a flattening of the waveform. Snoring is evident, and it
ends with an arousal. It is clearly different from the breathing
pattern in the remainder of the tracing. But there is little if any
change in oxygen saturation associated with the event. Prior to
October, 2012, this event would be scored as a hypopnea only in
centers where rule 4B, the alternative hypopnea scoring rule was
used. It would be scored as a respiratory effort-related arousal
(RERA) in centers where RERAs were scored and rule 4A, the
recommended hypopnea scoring rule, was used. And in some
centers it would not be scored at all.
Respiratory scoring was not part of the 1968 Rechtschaffen and
Kales scoring manual. Block and colleagues are credited with
the first definition of hypopnea in 1979 as a period of shallow
breathing causing oxygen desaturation. The first attempt to
define the spectrum of sleep related breathing events was the
so-called “Chicago Consensus,” published in 1999. This defined
an apnea hypopnea event as a clear decrease (> 50%) of a valid
measure of breathing during sleep lasting 10 seconds or a clear
amplitude reduction of a validated measure of breathing during
sleep that does not reach the above criterion but is associated
with either an oxygen desaturation of >3% or an arousal and
lasting more than 10 seconds. The Consensus group felt that
differentiation between apnea and hypopnea was not necessary.
The Consensus was never generally accepted, in part because
thermal flow sensors and expired CO2 monitors were not
considered part of the “valid measure of breathing” requirement.
Medicare was, at this point, still wedded to the 30 apnea rule and
using the new criteria would require separate scoring rules for
the elderly and young adults.
Drawing on data from the Sleep Heart Health Study, Meoli
RICHARD S. ROSENBERG, PHD
The 2007 American Academy of Sleep Medicine (AASM)
Scoring Manual revised the definition of hypopnea, allowing as
an alternative rule 4B and the possibility of scoring hypopnea
events without oxygen desaturation. In the accompanying
review, Redline and colleagues cited reliability of scoring as a
factor in the construction of a definition, noting that neither
oxygen desaturations nor arousals were highly correlated with
most outcomes measures. Proponents of oxygen desaturation
battled with arousal proponents and the compromise was that 2
definitions were included in the scoring manual, a recommended
and an alternative hypopnea scoring rule. A definition for
RERAs was provided, but scoring of these events was considered
optional. Furthermore, the International Classification of Sleep
Disorders, Second Edition includes all “scoreable” respiratory
events in the definition of the obstructive sleep apnea syndrome.
Dr. Richard Berry had the task of finding a consensus for the
latest revision of the AASM Scoring Manual. He describes the
final result as follows:
Although there were dissenters, the task force reached consensus
on a definition of a hypopnea rule in adults using a 30% drop in
the nasal pressure excursion for 10 seconds or greater associated
with ≥ 3% desaturation OR an arousal. The majority of the task
force felt that a hypopnea definition based only on desaturation
would result in misdiagnosis of some patients in whom
respiratory events fragment sleep but result in minor drops in the
SpO2.
Admittedly the evidence is poor, but there is some evidence for
an association between oxygen desaturation and cardiovascular
outcomes in patients with sleep apnea. There is also some
evidence that arousals and sleep fragmentation with apnea
are associated with decreased alertness during the day and
diminished quality of life indicators. The Scoring Manual Task
Force wrestled with these issues and elected to find either
measure adequate for the identification of events. The final
rule is based on consensus. Many if not all of the Task Force
members had personal experience with patients who were
decidedly symptomatic yet failed to meet the quantitative criteria
for treatment. Many of the events previously scored as RERAs
A2 Zzz 22.1 | March 2013
 Continued on Page 28
Richard S. Rosenberg, PhD, has
been in the sleep field since 1972
and currently lives in Long Beach,
Calif., where he works remotely as
educational development coordinator
for the American Association of Sleep
Technologists.
and colleagues proposed a definition that included a 10 second
event with a 30% reduction in amplitude of flow or effort and
a 4% oxygen desaturation. The brief paper cited evidence of
reliable scoring and association with cardiovascular outcomes.
Interestingly, this data was part of the Sleep Heart Health Study
and used an out of center testing device for “polysomnographic”
data collection. This definition was accepted by Medicare and
allowed treatment of a much larger population of the elderly. It
was quickly adopted by most private insurers as well.
 Continued from Page 27
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FIGURE 1
will now be scored as hypopnea and included in the apnea/
hypopnea index. Endorsing a definition that allows either oxygen
desaturation or arousal will clearly increase the number of
patients who qualify for treatment. Look at the event in Figure
1. I would call it an event, and my guess is that having frequent
events like that would not be good for you. Dr. Christian
Guilleminault has been saying this for decades. The field of
sleep medicine must now use the new hypopnea scoring rule and
collect evidence to demonstrate an association with outcomes
and ability to score hypopnea events reliably.
5.
Iber C, Ancoli-Israel S, Chesson A, Quan SF, for the
American Academy of Sleep Medicine. The AASM
manual for the scoring of sleep and associated events:
Rules, terminology and technical specifications.
Westchester, IL: American Academy of Sleep Medicine,
2007.
6.
Redline S, Budhiraja R, Kapur V, et al. The scoring of
respiratory events in sleep: Reliability and validity. J Clin
Sleep Med 2007;3(2):169-200.
7.
American Academy of Sleep Medicine. International
classification of sleep disorders: Diagnostic and coding
manual. 2nd ed. Westchester, IL: American Academy of
Sleep Medicine, 2005.
8.
Berry RB BR, Gamaldo CE, Harding SM, Marcus CL
and Vaughn BV for the American Academy of Sleep
Medicine. The AASM manual for the scoring of sleep
and associated events: Rules, terminology and technical
specifications. In: Version 2.0. Darien, Illinois: American
Academy of Sleep Medicine, 2012.
9.
Berry RB, Budhiraja R, Gottlieb DJ, et al. Rules for
scoring respiratory events in sleep: Update of the 2007
AASM Manual for the Scoring of Sleep and Associated
Events. Deliberations of the Sleep Apnea Definitions
Task Force of the American Academy of Sleep
Medicine. J Clin Sleep Med 2012;8(5):597-619.
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