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Methods of dierent sleep tests
EOG
EOG
https://t.me/medicina_free
EOG
EEG
EEG
EMG
Figure 4. Stage N2 sleep (NREM 2). Reproduced and modified from Riha (2012) with
permission.
EOG
EEG
EEG
Spindle K complex
waves
EMG
Figure 5. Stage N3 sleep (NREM 3). Note slow, high-amplitude δ-waves. Reproduced and
modified from Riha (2012) with permission.
Respiratory event scoring
Although scoring sleep using the EEG, EOG and mentalis/submentalis EMG has been
standardised since 1968 and more recently since 2007 (with multiple iterations in
the past 15 years), attempts to standardise the scoring of respiratory events were
made in 1999 and again in 2007. The reader is referred to the most recent version of
124
ERS Handbook: Respiratory Sleep Medicine
Methods of dierent sleep tests
EOG
ECG
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EOG
REMs
EEG
EEG
EMG
Sawtooth waves
Phasic twitch
Figure 6. Stage R (REM). Reproduced and modified from Riha (2012) with permission.
2.5 mV
EMG
31.3 µV
EOG(L)
250 µV
EOG(R)
250 µV
EEG
250 µV
100
SpO
2
50
THOR RES
×1
ABDO RES
×1
Nasal
airflow
×1
Airflow
×1
EMGdia-
phragm
62.5 µV
SOUND
×1
LEG(L)
20 mV
LEG(R)
20 mV
F
POSITION
B
L
R
Figure 7. 5-min page of PSG showing obstructive respiratory events (ObA) accompanied by
desaturations and arousals. THOR RES: thoracic respiratory band; ABDO RES: abdominal
respiratory band; F: front; B: back; L: le side; R: right side. Reproduced and modified from Riha
(2012) with permission.
the AASM manual for the latest scoring guidelines for respiratory events. Figures 7–9
summarise commonly recorded respiratory events.
With respect to sleep apnoea, severity is still classified according to AHI, at time of
publication. AHI is defined as the total number of apnoeas and hypopnoeas scored
during sleep, divided by the total sleep time in hours as recorded using the EEG. This
term should only be used when a PSG has been performed, not any other test.
125ERS Handbook: Respiratory Sleep Medicine
Methods of dierent sleep tests
ECG
ECG
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2.5 mV
EMG
15.6 µV
EOG(R)
250 µV
EOG(L)
250 µV
EEG
250 µV
100
PtcCO
2
mmHg
50
100
SpO
2
50
THOR RES
×1
ABDO RES
×1
Nasal
pressure
×1
Airflow
×1
EMGdia-
phragm
31.3 µV
SOUND
×1
LEG(L)
20 mV
LEG(R)
F
20 mV
B
L
POSITION
R
Figure 8. 5-min page of PSG showing hypopnoeas (Hyp) accompanied by desaturations on
the oxygen saturation trace. THOR RES: thoracic respiratory band; ABDO RES: abdominal
respiratory band; F: front; B: back; L: le side; R: right side. Reproduced and modified from Riha
(2012) with permission.
2.5 mV
EMG
15.6 µV
EOG(R)
250 µV
EOG(L)
250 µV
EEG
250 µV
100
SpO
2
THOR RES
×1
ABDO RES
×1
Nasal
pressure
×1
Airflow
×1
EMGdia-
phragm
62.5 µV
SOUND
×1
LEG(L)
20 mV
LEG(R)
20 mV
POSITION
50
F
B
L
R
Figure 9. 10-min page of PSG showing central apnoeas showing a CSR pattern. THOR RES:
thoracic respiratory band; ABDO RES: abdominal respiratory band; F: front; B: back; L: le side;
R: right side. Reproduced and modified from Riha (2012) with permission.
126
ERS Handbook: Respiratory Sleep Medicine
Methods of dierent sleep tests
https://t.me/medicina_free
Although work is being carried out to determine whether AHI is still the most
suitable ‘metric’ to classify the severity of SDB, at time of publication, it continues
to be classified as severe if the AHI is >30 events·h−1 of sleep, moderate if the AHI
is 15–30 events·h−1 of sleep and mild if the AHI is <15 and >5 events·h−1 of sleep.
What is important to bear in mind is that sleep eciency (the time actually slept
as scored on the EEG divided by the time in bed) can impact the AHI, raising it
significantly if low and diluting it if high. Additionally, little heed is currently paid
to the fact that age and sex can influence what might be considered normal values
within the general population with little impact discernible on generating symptoms
of sleep apnoea syndrome.
Scoring and reporting parasomnias and abnormal movements during sleep
There are a large variety of phenomena that occur during sleep ranging from what
might be considered normal (e.g. hypnic myoclonus, periodic limb movements), to
what might be considered abnormal and potentially harmful to the individual and/or
a co-sleeper (e.g. violent dream-enactment behaviour, sleep-walking). These activities
during sleep are described in the ICSD-3 classification (2014) under headings 5 and 6.
They may or may not impact on SDB and vice versa. Video-PSG can be vital to the
diagnosis of such disorders and provide clarification as to the sleep stage during which
they occur. Additional EMG montage is also contributory.
The reader is referred to the latest AASM scoring guideline and to the ICSD-3 for an
exhaustive guide on scoring and classification.
ECG evaluation
The ECG captured during PSG is generally in the form of a single rhythm trace. ECG lead
II is most frequently used with torso placement. However, depending on the study,
this can be modified. In adults, sinus tachycardia is defined as >90 beats per min and
bradycardia as <40 beats per min. Important information must not be overlooked in
respect of morphology, rhythm and rate captured as many cardiac abnormalities can
be silent and only picked up when sleep monitoring is performed.
The reader is referred to Hampton et al. (2019) for a detailed summary of normal and
abnormal ECG traces and the latest AASM guideline on cardiac rules during sleep.
Video monitoring during PSG
Using video to monitor the sleep period is almost universally implemented.
First, video monitoring provides protection for the patient and the sta during
a potentially vulnerable situation for both. The video is also used to capture any
behaviour witnessed during the PSG study, be it during wakefulness or during sleep.
It is indispensable in the case of diagnosing abnormal movements during sleep,
parasomnias and epilepsy.
Summary and interpretation of the PSG
Once scored, the consolidated output of the PSG is formatted and reported in a
standardised fashion, containing the most important information and observations from
the sleep period. Generally, the hypnogram is displayed, along with respiratory events,
body position, oxygen trace (with/without transcutaneous CO2 trace), sound if obtained,
leg movements, ECG and arousals in addition to a video report, a narrative about any
events occurring during the testing period and sleep period, and a table summarising
important numerical observations such as sleep onset latency, percentages of dierent
sleep stages, nadir oxygen saturation measured by pulse oximetry (S
), AHI, etc.
pO
2
127ERS Handbook: Respiratory Sleep Medicine
Methods of dierent sleep tests
Cn.A
RERA
Uns
Mx.H
Ob.H
Cn.H
Mx.A
Ob.A
Time
Hours
Epoch
Arousal graph
Sleep stage summary
Apnoea graph
Body position
Snoring
S
Time
Hours
Epoch
06:36:26
23:27:27
PLMs
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R
W
N1
N2
N3
12 am
0
6
23:27:27
+5
+5
+5
+5
+5
+5
+5
+5
100
pO
2
80
R
B
L
F
U
+5
+10
0
6
1
126
12 am 1 am 2 am 3 am 4 am 5 am 6 am
1
126
Figure 10. PSG report in a person without a sleep disorder (minor snoring with an AHI
<5 events·h−1), demonstrating normal sleep architecture, sleep progression and sleep cycling.
Cn.A: central apnoeas; Ob.A: obstructive apnoeas; Mx.A: mixed apnoeas; Cn.H: central
hypopnoeas; Ob.H: obstructive hypopnoeas; Mx.H: mixed hypopnoeas; Uns: unsure; RERA:
respiratory eort-related arousals; PLMs: periodic limb movements in sleep.
Figure 10 depicts a summary report page of a normal PSG scored using AASM (2007
and later rules) and figure 11 a PSG depicting severe sleep apnoea.
The PSG is used in the diagnosis or exclusion of SDB, disorders of central
hypersomnolence, parasomnias and abnormal movements during sleep. It is also
an important sleep research tool and provides information on sleep duration, sleep
amount, sleep cycling and amounts of dierent sleep stages and quality of sleep.
When interpreting and reporting the final PSG output summary, the method is
usually to first look at and comment on the hypnogram. Of interest are the sleep
architecture, sleep stage cycling, percentage of sleep stages (whether low or high),
sleep fragmentation, arousal index and periods of wakefulness. Keep in mind the
distribution of sleep stages across the lifespan and that various pathological states can
alter these. The second stage of interpretation comprises assessment for respiratory
abnormalities, ECG and movement traces in addition to abnormalities in oximetry,
128
P
(if performed), body position and relevance of sleep stage to these observations.
tcCO
2
Detailed examination of the raw data should be possible and is important in the case
of abnormal behaviours captured on video, such as seizures, parasomnias, etc.
1 am 2 am 3 am 4 am 5 am 6 am
2
246
2
246
3
366
3
366
4
486
4
486
ERS Handbook: Respiratory Sleep Medicine
5
606
5
606
6
726
06:36:26
6
726
7
846
7
846
Methods of dierent sleep tests
23:40:30 06:12:59
Cn.A
RERA
Uns
Mx.H
Ob.H
Cn.H
Mx.A
Ob.A
Apnoea graph
Sleep stage summary
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R
W
N1
N2
N3
+5
+5
+5
+5
+5
+5
+5
+5
pO
2
Body position
Snoring
PLMs
Time
Hours
Epoch
100
70
R
B
L
F
U
+5
+10
12 am 1 am 2 am 3 am 4 am 5 am 6 am
0
6
126
1
246
2
366
3
486
4
606
5
726
6
S
Figure 11. PSG report consistent with severe sleep apnoea. The hypnogram shows a paucity
of R-sleep and absence of N3 sleep, poor sleep cycling and sleep fragmentation. There is severe
arterial oxygen desaturation associated with repetitive obstructive events. For abbreviations,
see figure 10.
Limited channel/type III devices/respiratory polygraphy/home sleep
apnoea testing
Because SAHS is such a highly prevalent disorder among adults, less expensive, more
portable and more time-ecient methods of measuring the respiratory component of
PSG have been developed over the past 30 years.
Known as respiratory polygraphs (RP), polygraphy (PG), type III devices, cardiorespiratory monitors, limited channel studies and home sleep apnoea tests (HSAT),
they generally encompass technology developed to measure airflow, respiratory eort,
oxygen saturation and heart rate, to the exclusion of EEG. The great advantages of these
systems are price, portability and convenience to the patient. Although automated
scoring algorithms exist, as with PSG, manual scoring is still recommended.
These abbreviated forms of assessing primarily respiration during sleep generally
comprise a minimum of four channels: airflow, respiratory eort, oxygen saturation,
and pulse or heart rate. Previously, in this system one signal was one channel and one
sensor. In the context of ongoing technical innovations, one sensor will oen convey
several signals and represent several channels. One example is the nasal cannula,
which records pressure changes. However, derivations from this one sensor allow for
calculation of airflow, and if higher frequency vibrations are separated using adequate
filtering, then snoring can also be detected and recorded. Thus, one sensor produces
two signals and becomes two channels.
With reference to ongoing innovations in signal detection and processing, a new
classification system was proposed in 2011 to evaluate the physiological information
picked up by sensors. The SCOPER (Sleep, Cardiovascular, Oxygen, Position, Eort,
and Respiration) system was developed to reclassify the type I to IV channel counting
perspective of sleep recording systems in a more physiologically oriented manner,
129ERS Handbook: Respiratory Sleep Medicine
Methods of dierent sleep tests
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bearing in mind that one sensor might deliver diverse physiological information,
allowing for the definition of a reference standard with respect to physiological
information (such as EEG/EOG/EMG for sleep) at the top end and a lower accuracy
or surrogate measure (such as actigraphy for sleep) at the other end. Although this
classification is not evidence-based, it provides a scheme to assess the quality of
signals in terms of physiological information (table 7).
In summary, the recommended minimum number of signals to score respiratory
events accurately using current AASM criteria include heart rate, oximetry, nasal airflow
signals and respiratory eort bands. A position sensor should be used to dierentiate
supine from non-supine respiratory event severity. Peripheral arterial tonometry does
not measure airflow and may lead to misclassification of OSA at higher and lower
rates of SDB; it is likely to be most useful in younger patients with a high pre-test
probability of OSA and no significant comorbidities. Overall, the diagnostic accuracy
of the degree of OSA severity is significantly lower when using type III devices in an
unattended setting. Failure rates can be high, so it is important to keep a record of
reasons for failure and information on study quality. As stated earlier, manual scoring
is recommended, and a high-quality system should allow for manual editing of
automated scoring programs. The recent ERS technical standards for using type III
devices (limited channel studies) in the diagnosis of SDB in adults and children (Riha
et al., 2023), suggests that when undertaken in an attended setting, the sensitivity
and specificity for diagnosing OSA is suciently high with an AHI >10 events·h−1
irrespective of scoring criteria utilised.
Table 7. The SCOPER categorisation system
Sleep Cardiovascular Oximetry
S1: sleep by 3
EEG channels¶
with EOG and
chin EMG
S2: sleep by <3
EEG¶ with or
without EOG or
chin EMG
S3: sleep
surrogate, e.g.
actigraphy
S4: other sleep
measure
RIP: respiratory inductance plethysmography. #: proper oximetry sampling is defined as 3 s
averaging and a minimum of 10 Hz sampling rate (25 Hz desirable). ¶: three EEG channels defined
as frontal, central and occipital. Reproduced and modified from Collop et al. (2011) with permission.
C1: more than 1
ECG lead – can
derive events
C2: peripheral
arterial
tonometry
C3: standard ECG
measure (1 lead)
C4: derived pulse
(typically from
oximetry)
C5: other cardiac
measure
O1: oximetry
(finger or
ear) with
recommended
sampling
O1x: oximetry
(finger or
ear) without
recommended
sampling
(per Scoring
Manual) or not
described
O2: oximetry
with alternative
site (e.g.
forehead)
O3: other
oximetry
#
Position Eort
P1: video
or visual
position
measurement
P2: non-visual
position
measurement
E1: 2 RIP belts
E2: 1 RIP belt
E3: derived
eort (e.g.
forehead versus
pressure, FVP)
E4: other eort
measure
(including
piezo belts)
130
ERS Handbook: Respiratory Sleep Medicine
Methods of dierent sleep tests
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Additionally, it is important to note that published information on the acceptability,
sensitivity and specificity of type III studies in populations other than obese, middleaged men with symptoms consistent with OSA is limited. User-friendliness (for both
clinician and patient) and ease of scoring and setting up the equipment should be a
strong consideration when incorporating type III devices in the diagnostic pathway
of a sleep centre. This includes assessing the quality of the sensors and scoring
soware, disposable and non-disposable consumables, cleaning protocols, patient
acceptability and device reliability. If the clinical suspicion of OSA is high, patients
should be advised of the risk of having to repeat the study or undertake PSG to make
an accurate diagnosis, particularly if the study is unattended.
Regarding terminology used in the reporting of type III studies, the term ‘AHI’ should
not, by virtue of the absence of the EEG, be used to describe the summary of breathing
events acquired. According to the 2023 ERS technical standards more suitable terms
include one of the following:
• Apnoeas+hypopnoeas per estimated hours asleep
• Respiratory events index (per estimated hours asleep)
• Apnoeas+hypopnoeas per estimated hours of monitoring time
For further and more detailed discussion of type III devices used in the screening and
diagnosis of SDB, the reader is referred to the 2023 ERS technical standards (Riha
et al., 2023).
Type IV studies
Type IV studies generally comprise one to two sensors, one of which will be oximetry
and the other will be airflow, pulse rate or tracheal sound. Oximetry as a stand-alone
test is also used for screening for SDB (table 8). It is portable, relatively cheap, and
minimally obtrusive for patients. The usual indices derived from pulse oximetry
undertaken whilst asleep include the oxygen desaturation index (ODI), the cumulative
time below a certain saturation level, and minimum and mean saturation values
during the monitoring period. The ODI has shown significant complementarity with
other cardiorespiratory signals related to OSA, such as pulse rate and respiratory
events. Newer measures of hypoxaemia have become more prevalent in the past
decade, including hypoxic burden indices (saturation impairment time, desaturation
Table 8. Methods and parameters in conventional interpretation of the oximetry trace in SDB
Method Parameters evaluated
Visual inspection Recurrent drops in the S
S
data histogram and
pO
2
simple statistics
Intermittent hypoxaemia ODI: 3% or 4% in adults
Persistent hypoxaemia Overnight minimum saturation
Reproduced and modified from Álvarez et al. (2022) with permission.
profile during the night
pO
Saw-tooth pattern
Clusters of desaturations
Mean (central tendency), variance (dispersion), skewness
(asymmetry), kurtosis (peakedness)
Median (central tendency), quantiles, and interquartile
range (dispersion)
Delta index (variability measure)
Percentage of cumulative time spent with a saturation
below a threshold: 80–90% in adults
2
131ERS Handbook: Respiratory Sleep Medicine
Methods of dierent sleep tests
https://t.me/medicina_free
severity, hypoxia load, and hypoxic burden), which are considered complementary
to AHI/ODI and conventional hypoxaemia measures (cumulative time below 90%
(CT90) and minimum saturation).
Evidence-based technical specifications for oximetry deployed in the diagnosis and
screening of SDB do not exist. However, it is recommended that a minimum sampling
rate should be 10 Hz and desirable sampling rate should be 25 Hz with an averaging
of three values and the accuracy ±2%. A resolution of 0.1% is desirable, but not
specified in the AASM.
The sensitivity and specificity of using oximetry alone in the diagnosis of sleep apnoea
has been shown to range from 30–100%, depending on the machine utilised, the
population tested, whether the study is attended or unattended, and whether the
technique is combined with additional questionnaires or other forms of screening to
ascertain pre-test probability of SDB.
As such, it is a single parameter technique which also has no redundancy in the system
to capture respiratory and sleep signals should it fail and it is prone to misinterpretation.
It should not be relied on as a diagnostic technique in isolation, but may be useful in
certain circumstances where there is a high suspicion of sleep apnoea, for monitoring
progression of diseases resulting in nocturnal desaturation/hypoventilation, and for
monitoring response to therapy in the context of a known diagnosis.
Further reading
• Álvarez D, et al. (2022). Oximetry indices in the management of sleep apnea: from overnight
minimum saturation to the novel hypoxemia measures. Adv Exp Med Biol; 1384: 219–239.
• American Academy of Sleep Medicine (2014). The International Classification of Sleep Disorders:
Diagnostic and Coding Manual. 3rd Edn. Darien, American Academy of Sleep Medicine.
• Collop NA, et al. (2011). Obstructive sleep apnea devices for out-of-center (OOC) testing:
technology evaluation. J Clin Sleep Med; 7: 531–548.
• Hampton J, et al. (2019). The ECG Made Easy. 9th Edn. Elsevier Health.
• Hirshkowitz M. (2004). Normal human sleep: an overview. Med Clin North Am; 88: 551–565.
• Mattice C, et al. (eds) (2020). Fundamentals of Sleep Technology. 3rd Edn. Philadelphia,
Wolters Kluwer Health.
• Pretto JJ, et al. (2014). Clinical use of pulse oximetry: ocial guidelines from the Thoracic
Society of Australia and New Zealand. Respirology; 19: 38–46.
• Rechtschaen A, et al. (1968). A Manual of Standardised Terminology, Techniques and Scoring
System for Sleep Stages of Human Subjects. Bethesda, National Institutes of Health.
• Riha RL (2012). Polysomnography. In: Simonds AK, et al. ERS Handbook of Respiratory Sleep
Medicine. Sheeld, European Respiratory Society; pp. 120–130.
• Riha RL, et al. (2023). ERS technical standards for using type III devices (limited channel
studies) in the diagnosis of sleep disordered breathing in adults and children. Eur Respir J; 61:
2200422.
• Standards of Practice Committee of the American Sleep Disorders Association (1994). Practice
parameters for the use of portable recording in the assessment of obstructive sleep apnea.
Sleep; 17: 372–377.
• Troester MM, et al. (2023). The AASM manual for the scoring of sleep and associated events:
rules, terminology and technical specifications: version 3. Darien, American Academy of Sleep
Medicine.
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ERS Handbook: Respiratory Sleep Medicine
Limitations of oximetry
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and respiratory polygraphy
in comparison with
hospital-based PSG studies
Renata L. Riha
PSG undertaken in a hospital-based setting is considered the gold-standard sleep
test, largely because all sleep, respiratory and movement parameters are monitored
simultaneously, with video, direct observation, and assistance to the patient available
throughout the testing period. However, it is expensive and time-consuming and
may not always reflect the natural sleep state of the patient. Unfortunately, despite
their advantages, the more abbreviated methods of testing for SDB also have several
limitations which are discussed below.
Type III devices/respiratory polygraphy
In attended settings, type III devices have a high sensitivity and specificity for diagnosing
SDB. In unattended settings, they should be considered as screening tools due to a
high number of errors that can emerge when a patient is allowed to independently
apply the sensors in their own environment. Accuracy is also determined by the
degree of clinical pre-test probability of SDB.
However, irrespective of the setting of the test, the greatest limitation lies in the
absence of EEG. Therefore, any scoring of respiratory events using current American
Academy of Sleep Medicine (AASM) guidelines cannot incorporate arousals to score
hypopnoeas and obstructive events with no, or minimal, oxygen desaturations.
There is no accurate method for reporting sleep, and thus, total recording time is
oen used as the denominator to calculate respiratory event frequency or the oxygen
desaturation index (ODI). The dierence between the mean total recording time and
mean total sleep time ranges between 1 h and 3 h in the literature.
Key points
• In comparison to hospital-based PSG, type III studies lack EEG-defined sleep
as a denominator for respiratory events.
• Type III studies that are undertaken in an unattended setting may have high
failure rates and should be considered as screening tools only.
• Oximetry with or without one additional channel should be considered as a
screening tool only in patients with a high probability of SDB.
• Interpretation of oximetry can never be anything other than an assumption as
to the type and cause of SDB.
133ERS Handbook: Respiratory Sleep Medicine
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