Biomedical Engineering Reference
In-Depth Information
Alternatively, a hypopnea can also be scored if all of these criteria are present:
The nasal pressure signal excursions (or those of the alternative hypopnea sen-
sor) drop by
50% of baseline.
The duration of the event is at least 10 seconds.
There is a
>
3% desaturation from preevent baseline or the event is associated
with arousal.
At least 90% of the event's duration must meet the amplitude reduction of cri-
teria for hypopnea.
>
Respiratory events that do not meet criteria for either apnea or hypopnea can
induce arousal from sleep. Such events have been called upper-airway resistance
events (UARS), after the upper-airway resistance syndrome [11]. An AASM task
force recommended that such events be called
respiratory effort-related arousals
(
RERAs
). The recommended criteria for a RERA is a respiratory event of 10 seconds
or longer followed by an arousal that does not meet criteria for an apnea or
hypopnea but is associated with a crescendo of inspiratory effort (esophageal moni-
toring) [28]. Typically, following arousal, there is a sudden drop in esophageal pres-
sure deflections. The exact definition of hypopnea that one uses will often determine
whether a given event is classified as a hypopnea or a RERA.
One can also detect flow-limitation arousals (FLA) using an accurate measure of
airflow, such as nasal pressure. Such events are characterized by flow limitation
(flattening) over several breaths followed by an arousal and sudden, but often tem-
porary, restoration of a normal-round airflow profile. One study suggested that the
number of FLA per hour corresponded closely to the RERA index identified by
esophageal pressure monitoring [33]. Some centers compute a respiratory arousal
index (RAI), determined as the arousals per hour associated with apnea, hypopnea,
or RERA/FLA events [10]. The AHI and respiratory disturbance index (RDI) are
often used as equivalent terms. However, in some sleep centers the RDI
+
RERA index, where the RERA index is the number of RERAs per hour of sleep and
RERAs are arousals associated with respiratory events not meeting criteria for
apnea or hypopnea.
One can use the AHI to grade the severity of sleep apnea. Standard levels include
normal (
=
AHI
30) per hour. Many
sleep centers also give separate AHI values for NREM and REM sleep and various
body positions. Some patients have a much higher AHI during REM sleep or in the
supine position (REM-related or postural sleep apnea). Because the AHI does not
always express the severity of desaturation, one might also grade the severity of
desaturation. For example, it is possible for the overall AHI to be mild but for the
patient to have quite severe desaturation during REM sleep.
<
5), mild (5 to
<
15), moderate (15 to 30), and severe (
>
10.11
Pediatric Respiratory Definitions
Periodic breathing is defined as three or more respiratory pauses of at least 3 seconds
in duration separated by less than 20 seconds of normal respiration. Periodic breath-
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