How to Interpret Your Sleep Study
The sleep studies include “Diagnostic Studies,” “Split Night studies,” “Full Night CPAP/BiPAP/ASV titration studies,” and daytime
“MWT/MSLT studies.” Each Peninsula Sleep Center’s report has two summary pages and 3-7 pages of tables and graphs. Essentially, it reports the sleep architecture (brain EEG), oxygen saturation, cardiac events, respiration during sleep, snoring, as well as leg movements during sleep.
The following information may help to explain more about your sleep study report:
Normal Sleep Stages
Stage N1 2-5% (up to 8%) of total sleep time
Stage N2 45-55% of total sleep time
Stage 3 3-8%
Stage 4 10-15%
Stage REM 20-25%*Stage N3 is Stage 3+ Stage 4 = 13-23%
Stage N2 45-55% of total sleep time
Stage 3 3-8%
Stage 4 10-15%
Stage REM 20-25%*Stage N3 is Stage 3+ Stage 4 = 13-23%
(Source: Principles and Practice of Sleep Medicine by Kryger, Roth, Dement 2005)
Normal Oxygenation
• Oxygen saturation: normal: greater than 90-92%
• Oxygen saturation may remain normal despite respiratory events
• Oxygen saturation may remain normal despite respiratory events
and EEG arousals.
• Intermittent hypoxemia means fluctuations of oxygen saturation in
blood due to cessation of air flow. This may be measured by the
time in low saturation or by the number of occasions that oxygen
saturation drops. The latter is called desaturation index (DI), which
is the number of times per hour of sleep when the O2 saturation
decreases by 4% or more.
Respiration
• Apnea: Complete cessation of breathing for 10 seconds or more.
• Apnea could be due to closure of the throat (Obstructive), or lack
• Apnea could be due to closure of the throat (Obstructive), or lack
of respiratory effort by brain (Central).
• Hypopnea: Breathing may become significantly shallow to a degree
that blood oxygen saturation decreases. When this continues for
more than 10 seconds, it is called hypopnea.
• RERA: Shallow respiration that causes only arousals from sleep is
• RERA: Shallow respiration that causes only arousals from sleep is
called “Respiratory Effort-Related Arousals” (RERA). This does
not affect the oxygen saturation.
• The number of the above per hour of sleep is called an “index,”
i.e. Apnea Index, Hypopnea Index, and RERA Index. Apnea-
Hypopnea Index (AHI) is the number of apneas and hypopneas per
hour of sleep time. “Respiratory Disturbance Index” (RDI) is the
sum of all the 3 event forms.
• An RDI of 5 or greater is needed for diagnosis of Sleep Apnea.
(Source: International Classification of Sleep Disorders (ICSD-2) and 2007 AASM Manual for Scoring)