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J. Verbraecken
enced to the mastoid (M) electrode. The EMG of the submental muscles is
recorded from two skin electrodes placed at a location near the chin close to
these muscles.
According to international standards, at least four neurophysiological signals are
required, one EEG, two EOG, and one chin EMG channel. Consequently, based on
the information obtained by EEG, EMG, and EOG, sleep stages can be scored
according to the AASM criteria [3]. Ventilation is often measured qualitatively by
means of thermistors, but can be assessed more precisely with nasal pressure cannulas, or eventually by means of calibrated respiratory inductance plethysmography [4]. Breathing effort can also be detected by recording movements of chest and
abdomen, surface EMG, peripheral artery tonometry (PAT), and changes in pulse
transit time (PTT), but most effectively by detection of intrathoracic pressure
swings. These swings can be detected invasively by measuring esophageal pressure. Currently, movements of chest and abdomen are most often recorded by
respiratory inductance plethysmography (RIP), while few systems still rely on
strain gauges, which detect changes in resistance according to length changes. RIP
is an evaluation technique which makes use of belts at thorax and abdomen, with
an inbuilt electrical wire. This wire behaves as a coil and the features of the coil
change when the belt is stretched. The signal is in phase with volume changes of
the chest (and abdomen) and changes almost linearly with increasing tidal volume.
If respiratory effort is detected during an apnea, this can be explained by obstruction of the upper airway. An overview of the features of these ventilation sensors,
with their advantages and disadvantages is shown in Table 7.1. Transcutaneous
oxygen saturation is measured by means of pulse oximetry (eventually combined
with transcutaneous or end-tidal PCO2 measures). Sound recording is an indirect
method to detect ventilation. Most often, body position (position sensor on the
chest) is also registered. Today’s sleep laboratories continue to undergo technologic evolution, particularly related to the increased reliance on digital systems,
and improved algorithms for automatic analysis based on articial intelligence [5].
Table 7.1 Physical characteristics of widespread sensors used to assess ventilation during clinical
sleep studies
Type
Airow sensors
Thermistors Records temperature
Physical characteristics Advantages
changes induced by
breathing
Changes depend on
environmental temperature
and on mass/inertia of
temperature probe
Flow/temperature changes
are not linear—Extremely
difcult to get them linear
Assessment
of both nasal
and oral
airow
Cheap
Less effective
when
breathing
through the
mouth
Disadvantages
Thermistor signal is not
well correlated with breath
amplitude
Consequently, not
quantitative, therefore
useless in practice
Generally resulting in
overestimation of the real
ow
Inadequate to detect ow
limitation
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Table 7.1 (continued)
Type
Nasal cannulas Detects air pressure changes
Effort sensors
Strain gauges A strain gauge or load cell
Respiratory
induction
plethysmography
(RIP)
Peripheral arterial
tone (PAT)
Physical characteristics Advantages
Flow/pressure changes are
nonlinear—Easy to make it
linear
More sensitive than
thermistors for detecting
hypopneas and
hypoventilation
Nasal cannulas have a better
negative predictive value
and a poorer positive
predictive value than RIP
is a device used to measure
strain on an object. Small
voltages are induced in
response to movement
The sensors are connected
with the belts that are placed
around chest and abdomen
Detects changes in volume
of chest and abdomen
during inspiration and
exhalation
The RIP belts are embedded
with wires, woven in a
sinusoidal pattern around the
body. An electrical current
applied to the wires generates
an oscillating signal, in
response to variations in
resistance associated with
changes in body
circumference (and behaves
like an induction spindle).
Analysis of the RIP chest and
abdominal channels can
indicate a hypopnea
Utilizes the changes in
peripheral vascular
resistance and oximetry as
indirect measures of
respiratory signals
Disadvantages
Quantitative
Able to detect
subtle
changes in
ow (ow
limitation)
Cheap Poorly validated
Quantitative
Quite linear
Comfortable
for subject to
wear
Few loss of
signals
No signal when breathing
through the mouth
Not linear
Disposable materials
Currently positioned as an
obsolete technique, but
still used by some systems
Calibration is difcult
(especially in obese
patients)
Costs of belts can rise
Relatively expensive
compared to other
respiratory sensors
Contraindication when
presence of atrial
brillation and use of
alpha blockers
Devices utilize two nger
probes: a PAT probe and
an oximetry probe—Worn
on separate digits of the
same hand
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(continued)
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Table 7.1 (continued)
Type
Pulse oximetry
Physical characteristics Advantages
Two types:
– Transmissive pulse
oximetry (or
transmission pulse
oximetry): In this
approach, a sensor
device is placed on a
thin part of the
patient’s body
(ngertip, earlobe, or
an infant’s foot)
– Reectance pulse
oximetry (or
reection pulse
oximetry): Does not
require a thin section
of the person’s body
(application on the
feet, forehead, and
chest). The light
sources and the
photodetector are
located on the same
surface of the skin
Oxygen saturation is
estimated by the change in
light wavelength between
oxygenated and
deoxygenated blood in a
pulsatile ow. The oximeter
probe emits a light that
shines through the nail bed
and is picked up by a light
detector on the opposite side
of the nger
Simplicity of
use and
ability to
provide
continuous
and
immediate
oxygen
saturation
values
Accurate
down to about
70–80%
There is good
agreement
between
indices of
OSA that
require ≥4%
oxygen
desaturation
J. Verbraecken
Disadvantages
Erroneously low reading
or false reading may be
caused by hypoperfusion
of the extremity or from
vasoconstriction, incorrect
sensor application, highly
calloused skin, nail Polish,
extraneous light intrusion,
misalignment/
misplacement, movement
Error rates may be higher
for adults with dark skin
color
COPD may cause false
readings
Pulse oximeters differ in
their ability to provide
accurate data during
conditions of motion or
low perfusion
In patients with a slow heart
rate, a little longer averaging
time may be needed (at least
a 3-beat average)
Nadir in SaO
follows apnea or hypopnea
termination by
approximately 6–8s,
secondary to circulation
time and instrumental delay
Oximeters average over
several cycles before
producing a reading
Oximetry estimate of heart
rate may be much lower
than the actual rate if the
patient has atrial
brillation or frequent
premature beats (only
every other beat may
provide sufcient signal to
oximetry probe for the
oximetry software to
detect a heartbeat
In measuring dynamic
events (apneas), different
pulse oximeters do not
record identical values
There is a uctuation
range of up to factor 1.42
between devices
usually
2
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For years, there is also a move to collect data outside of the traditional sleep laboratory setting. Respiratory polygraphy (PG) is performed when one does not include
signals such as EEG, EMG, and EOG.This shift is driven by the limited available
capacity to perform PSG in the hospital, economical considerations, and the need
to assess sleep in the patient’s natural sleep environment. To overview this process
and direct the patient, sophisticated knowledge of equipment and management procedures is required [6, 7]. This chapter is a review of the clinical aspects of PSG
and PG, with some technical aspects in addition. We will also put some emphasis
on sleep trackers/wearables and will address new evidence on in-depth ow shape
analysis to demonstrate epiglottic collapse.
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7.2 In-Lab Attended Polysomnography
In-lab attended PSG is the gold standard technique for assessing sleep-related
breathing disorders, including obstructive and central sleep apnea and nocturnal
hypoventilation [4]. A sleep study offers in-depth information about both sleep
structure and the disturbances in ventilation. Also, data on heart rate, body position,
muscle tone, and sleep-related limb movements are obtained. If combined with an
audiovisual recording of the sleeping subject, this is called a video PSG.Setting up
a PSG requires substantial health care resources, adequate facilities, and experienced medical/paramedical staff. Ideally, the PSG should be performed during the
usual sleep period, in order not to interfere with the patient’s circadian sleep-wake
rhythm. Questionnaires regarding sleep-wake behavior and a sleep diary that solicits information about major sleep-wake periods and naps are useful adjuncts to PSG
[8]. Of interest, many patients also report difculties initiating and/or maintaining
sleep and have a subjective total sleep time and quality that is at odds with the objective data assessed in the laboratory (referred to as sleep state misperception). This
nding warrants that subjective data be collected systematically, as part of the sleep
laboratory evaluation.
PSG is indicated for the diagnosis of sleep-related breathing disorders, including
the setup and evaluation of positive airway pressure therapy (PAP), treatment and
the evaluation of other treatments (mandibular advancement devices—MAD, surgery); for the evaluation of hypersomnia, including suspected narcolepsy together
with a multiple sleep latency test (MSLT), and for the evaluation of sleep-related
violent behaviors (or otherwise damaging the patient) [8–10]. More particularly, it
can also be indicated for neuromuscular conditions with sleep-related symptoms,
and for an assessment of epileptiform sleep interruptions or paroxysmal arousals.
Opposite to some current practice, PSG is not a standard indication for chronic
pulmonary disorders, epilepsy without sleep-related complaints, typical parasomnia, or for the determination of restless legs, circadian sleep-wake rhythm disorders,
depression or rst-step assessment of insomnia [8–10].
An in-lab attended PSG fully observed by a sleep technician is the standard technique for assessment of obstructive sleep apnea (OSA). In several guidelines, the
following supporting statements have been mentioned [8–10]:
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• Up-to-date monitoring with extensive registration of ow, respiratory effort,
oxygen saturation, heart activity, sleep position, sound, limb movements, sleep
features as well as audiovisual observation, etc.
• A single-night diagnosis performed under attended conditions, so that the test
has technical failures (sensor loosening or shifting) by exception.
• Assessment of the effective total sleep time and the simultaneous exact index
calculation (including AHI, ODI, sleep efciency), particularly with comorbid
insomnia.
• Sleep disorders can be comorbid; other sleep disorders, especially central sleep
apnea syndrome, parasomnia and periodic leg movement disorder can be disen-
tangled with PSG.
• Obtained information is also useful in the presence of clinically relevant
comorbidities (chronic obstructive pulmonary disease—COPD, restrictive
lung function disorders, systolic or diastolic heart failure and obesity-hypoven-
tilation), since an association can occur during REM sleep or extra sensors can
be applied.
• Loss of data rarely occurs, and instantaneous scoring can eventually be done by
the attending sleep technician. Optionally, a “split night” approach can be offered
when PAP titration is urgently needed.
• PSG can also be considered for medico-legal reasons, such as the workup of
patients with cardiorespiratory problems and risk of injury in disabled or disori-
ented people and in subjects with sleep-related violent behavior.
J. Verbraecken
Generally spoken, in-lab attended PSG is a cost-benet proof examination.
7.3 Report Format
To take advantage of the results of (video) PSG, the report must meet a number of
quality requirements [11]. The PSG report should denitely include information
about sleep: sleep times in relation to bedtime, respiratory events like apneas,
hypopneas with and without oxygen saturation, its association with body posture
and sleep stages, and oxygen saturation (mean, nadir, oxygen desaturation index—
ODI, and time <90%) and presence of rhythmic disorders (with or without arousals). An extensive overview of PSG variables and content of an ideal PSG report is
shown in Tables 7.2 and 7.3. Critical data must be displayed properly and clearly in
tables and graphs. The data must not be amenable to interpretation. Description of
the subjective experience of the sleep during the PSG is an integral part of the PSG
report. This information allows evaluating whether sleep quality during the analysis
was comparable, better or worse than has usually been. Since the results depend on
the way in which the sleep and sleep-related events are evaluated, it is necessary to
report the scoring method used, which is currently the AASM 2007 (for sleep EEG)
and 2012 edition and updates (for respiratory events) [3, 12–14]. It is also common
practice to verify and correct any automatic analysis of signals by using visual scoring. Nighttime trends or graphic display of raw data (f.i. O2 saturation curve),
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Table 7.2 Denitions of PSG variables
Sleep
Lights out (time) Clock time when the technologist turn the lights out for the
patient to go to sleep
Lights on (time) Clock time when the technologist turns the lights on at the
end of the study
Time in bed (TIB) (in minutes) Time from “lights out” to “lights on”
Total sleep time (TST) (in
minutes)
Sleep (onset) latency (in
minutes)
REM sleep latency (in
minutes)
Sleep efciency (percentage) The amount of time spent sleeping expressed as percentage
WASO (in minutes) Wake after sleep onset (the amount of time spent awake after
Arousal index (number/hour) Amount of arousals per hour of TST
Breathing
Obstructive apneas (number) The total number of obstructive sleep apneas during the night
Central apneas (number) The total number of central sleep apneas during the night
Mixed apneas (number) The total number of mixed sleep apneas during the night
Hypopneas (number) The total number of hypopneas during the night
AHI (number/hour) Apnea-hypopnea index, calculated by adding the apneas and
AI (number/hour) Apnea index, calculated by taking the number of apnea
SpO
2
Mean SpO2 (%) The mean oxygen saturation for the entire night
Min SpO2 (%) The nadir or lowest oxygen saturation value for the entire
TimeSpO2 <90% (or CT90%)
(in minutes)
ODI (number/hour)
ODI3 and ODI4 (number/hour)
Limb movements
PLMI (number/hour) Periodic limb movements per hour of TST.Repetitive muscle
PLMAI (number/hour) Periodic limb movements associated with microarousal per
Amount of actual sleep between “lights out” and “lights on”
Time from lights out to the rst of three continuous epochs of
stage N1 or any other sleep stage.
Time from lights out to the rst epoch of stage REM
of TIB
sleep onset)
hypopneas during the night and dividing it by TST
events during the night and dividing it by TST
night
Parameter to express global degree of hypoxemia
Number of oxygen desaturations per hour of TST (≥3% or
≥4%)
contractions (0.5–5s) separated by an interval of 5–90s
hour of TST
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computer analysis (f.i. EEG power in different spectral bands), and scored events
(f.i. hypnogram, arousals, respiratory events) are extremely important (Fig.7.1):
• To get a general and instant impression on the time course of the studied variables and to demonstrate the interaction with the other parameters.
• To allow quality control: the trend demonstrates at a glance whether the obtained
signals are of sufcient quality.
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Table 7.3 Overview of the parameters in an ideal PSG report
Administrative data
Recorded parameters
Sleep architecture:
• Lights off—Lights on; rst and last sleep epoch
• TIB—TST—SEI
• Sleep latency times (NREM, REM)
• Time spent in different sleep stages
• WASO, shift in sleep stages, micro- and macroarousals, arousal index, PLM-arousal
index (PLMAI)
Respiratory data:
• Used scoring method
• Number of respiratory events and duration (mean, longest event)
• Separation between obstructive, central, and mixed apneas
• Respiratory effort-related arousals (RERAs)
• Respiratory indices based on body position (AHI supine vs. AHI nonsupine) and sleep
stages (AHI-REM vs. AHI-NREM)
• Snoring with respect to body position and sleep stage
• Data with respect to oxygen saturation (mean, nadir, SaO2<90%, SaO2<88%)
• Presence of Cheyne-stokes breathing
• Snoring intensity (subjectively, based on video; objectively, based on decibelometry)
Movement activity:
• Periodic limb movements (PLMS)
• Restless legs (RLS)
• Motoric activity during REM sleep
• PLMI (periodic limb movement index)
• PLMAI (periodic limb movement arousal index)
ECG events
EEG events (sleep fragmentation, alpha-delta pattern, alpha intrusion, inuence of drug intake,
signal quality)
J. Verbraecken
Fig. 7.1 Polysomnographic trend in a patient with severe obstructive sleep apnea
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The following parameters and trends can be used:
1. Trends with respect to the neurological activity:
• Time course of alpha- and delta-power.
• PLMS, based on low legs EMG or actimetry.
• Hypnogram.
• Arousals.
2. Trends with respect to the cardiac and respiratory activity:
• SaO2, respiratory event, sound.
• Heart activity based on RR-interval (brady-tachycardia patterns).
• Body position.
To evaluate a PSG performed in another sleep lab, it is preferable to have a detailed
report with nighttime trends available, or to perform a reanalysis with one’s own
software. The European Data Format (EDF) allows to exchange raw data between
sleep centers which use different software packages [15].
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7.4 Ambulatory PSG/PG
Due to the high prevalence of sleep-related breathing disorders in the general public, long waiting lists for diagnostic sleep studies exist in most sleep centers [16]. To
tackle this problem, equipment for ambulatory sleep studies has been designed,
with a focus on diagnosing OSA.A plethora of studies has been performed to evaluate its reliability and specicity versus the gold standard technique [17, 18]. In the
following paragraphs, its use in OSA will be discussed, with emphasis on the indications for diagnosing or ruling out OSA and the strengths and limitations. In real
life, each tool has its specic place in the diagnostic area.
7.4.1 Equipment forAmbulatory PSG/PG Versus theGold
Standard Approach
Technically spoken, PSG/PG can be conducted in the patient’s natural sleep setting.
It facilitates expansion of the measuring capacity, promoting faster access to the
test. Plenty of portable systems have been developed meanwhile. The main aim of
these systems is to evaluate (obstructive) sleep apnea and have not been extensively
evaluated for other indications. Currently, the systems are categorized according to
the parameters and sensors used in the presence or absence of a sleep lab technician
(Table7.4) [19]:
• Type 1: PSG fully supervised by a lab technician or by video, conducted at a
sleep clinic (sleep staging including EEG, EOG or chin EMG, limb movements,
ECG, heart frequency and respiratory measurements with oronasal airow, thoracoabdominal movements, and pulse oximetry). This is the gold standard.
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Table 7.4 Categorization of sleep studies according to the AASM
Type 1 Type 2 Type 3 Type 4
Ambulatory
respiratory
Standard supervised
PSG Ambulatory PSG
Parameters Minimum of seven,
including EEG,
chin EMG, EOG,
ECG, ow,
respiratory effort,
SpO
2
Positional
measurement
EMG OL Recommended yet
Supervision Yes No No No
Possibility of
interventions
Present Optional Optional No
optional
Yes No No No
Minimum of
seven,
including EEG,
chin EMG,
EOG, ECG,
ow,
respiratory
effort, SpO
Optional Optional No
polygraphy 4–6
channels
Minimum of four,
including
ventilation
(minimum two
channels for
respiratory effort, or
one for airow and
one for respiratory
2
effort, heart rate or
ECG, SpO
2
J. Verbraecken
Ambulatory
respiratory
polygraphy
1–3 channels
Minimum of
one for SpO2,
ow or
thoracic
movements
• Type 2: Unsupervised PSG (at the sleep clinic or at the patient’s home).
• Type 3: Patient registration where thoracoabdominal movements and airow in
addition to heart frequency or ECG plus the oximetry are recorded on several
channels (4–8).
• Type 4: Ambulatory recording using one to three parameters, usually including
pulse oximetry, but not meeting the criteria of type-3 monitors.
At the lower end, devices with even fewer channels, usually 1–3 channels (e.g.,
RUSleeping, ApneaLink) may record respiratory ow or movement, sometimes
even without pulse rate and oximetry. Oximetry is usually part of the methods
applied to screen for sleep-disordered breathing. One has to consider false-negative
results. Frequent short apneas can occur without signicant oxygen saturation dips,
f.i. in lean patients with sufcient oxygen reserves [20].
7.4.2 Why/Why Not Ambulatory PG/PSG?
Some of the direct expenses can be lowered or eliminated by sparing on supervision
and on the furnishing of the patient rooms. Such an economical approach may
sound attractive, but does not necessarily improve cost-effectiveness. Altogether,
additional costs are created by repeating sleep studies when ambulatory assessments are technically inadequate, or in negative studies with subjects who have high
suspicion of OSA [21]. The sleep comfort of the patient can be a plausible reason
for performing sleep testing in the home setting, partly due to the so called
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“rst- night effect” and a familiar environment for the patient. There is scientic
evidence for and against this setup. One concern could be that the ecological footprint of sleep studies will increase, due to extra travel time for patient or technician,
depending where the hook-up of electrodes will take place.
The drawback is that poorly working electrodes cannot be corrected and the
absence of supervision of eventual nocturnal behaviors complicates it interpretation. Failed measurements resulting from technical problems occur in 5–20% of the
studies [22]. Such failures can be avoided by proper instructions by skilled and
experienced workers, a choice of recorders with robust electrodes and proper sensor
hook-up. This could argue for applying a double ow sensor, as recommended by
the AASM in 1999 [4].
Lastly, and of major concern, if single polygraphy is performed, patients are
likely to have a 30% lower AHI on average, compared to patients investigated by
PSG [23]. PGs do not typically include EEG and thus cannot detect hypopneas that
lead only to an arousal without signicant O2 desaturation. This is especially important in patients who have a low body mass index (BMI) because they are more likely
to have respiratory events that lead to an arousal rather than desaturation [20]. Also,
a higher denominator is used in polygraphy to calculate the AHI.Therefore, polygraphy can result in underdiagnosis and misclassication of OSA.Some PGs have an
actigraph, which can be used as a surrogate marker for identifying when the patient
is awake and asleep [24]. These PGs are not widely available and are more cumbersome and expensive. Moreover, one must remember that this is only a surrogate
marker and can give awed results, particularly in the presence of other causes of
sleep fragmentation [24].
Taking all these limitations into account, nowadays ambulatory PSG is consid-
ered valid for the evaluation of a wide variety of sleep disorders, as long as video
recording or other peripheral equipment is not needed.
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7.4.3 Indications forAmbulatory PG: International Guidelines
The guidelines for portable sleep studies are only applicable to PG. PG can be
applied when there is a high suspicion of OSA [25], under the prerequisite that some
additional conditions are met. Such studies require manual scoring by a skilled
sleep lab technician allowing to receive reliable clinically useful data. PG has gained
increasing success in the last decade. In 2007, the AASM published a clinical guideline on the implementation of PG for the diagnostic assessment of OSA [6] which
forms the starting point for the current indications of PG.
7.4.4 Low or High Pretest Probability of(Obstructive)
Sleep Apnea
The use of PG is only recommended in patients with a clinically based low or high
suspicion of (obstructive) sleep apnea (low or high pretest probability), whereas it is
designated to use PSG to assess patients with an intermediate probability or patients
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