Pulmonology & Neurology & Sleep Medicine
Complete polysomnography (PSG)
Polysomnography (PSG) - a term derived from the Greek polys (several) + sleep sleep + graphein (write) - is the simultaneous and continuous recording of multiple physiological parameters during nocturnal sleep, constituting the reference examination for the objective exploration of sleep architecture and the diagnosis of sleep disorders. Performed in a sleep laboratory with a full night's recording (usually 7 to 8 hours) under the supervision of a sleep technologist, it simultaneously captures cerebral electrical activity (electroencephalogram - EEG), eye movements (electrooculogram - EOG), muscle tone (electromyogram - EMG of chin and lower limbs), respiration (oro-nasal airflow via thermistor and nasal pressure sensor + respiratory effort via thoracic and abdominal belts), oxygen saturation via pulse oximetry (SpO₂), heart rate via ECG, body position and limb movements. All these physiological signals are analyzed - manually by a sleep specialist or semi-automatically in line with AASM (American Academy of Sleep Medicine) recommendations - to stadify sleep into 30-second successive epochs (awake + N1 + N2 + N3 + REM sleep) and detect respiratory anomalies (apneas + hypopneas + respiratory effort-related arousals), motor abnormalities (periodic limb movements - PLM + abnormal motor activity in parasomnias) and electroencephalographic abnormalities (nocturnal epileptic activity). PSG is indispensable in several specific clinical contexts, but is not necessary in all cases of sleep disorder - for obstructive sleep apnea syndrome (OSAS) in adults without significant comorbidity, nocturnal oximetry testing or ambulatory home polysomnographic recording (type III or type IV according to the AASM classification) often constitutes an acceptable and less costly alternative, reducing the considerable waiting times for sleep laboratories in Quebec.
Settings saved and their meaning
- Electroencephalogram (EEG) — sleep staging: scalp electrodes (standard leads according to AASM recommendations) → recording of cortical electrical activity + stage N1 (drowsiness — alpha activity 8–12 Hz that fragments + predominant theta waves) + stage N2 (light sleep — sleep spindles 12–15 Hz + K complexes) + stage N3 (deep slow-wave sleep — delta waves > 75 µV + > 20 % of the epoch) + REM sleep (mixed low-amplitude rapid activity + sawtooth waves + muscle atonia + rapid eye movements)
- Electrooculogram (EOG): records eye movements → slow pendular movements in N1 + absence in N2-N3 + rapid eye movements — characteristic of REM sleep → diagnosis of REM Sleep Behavior Disorder (RBD — abnormal behavior during REM sleep) + diagnosis of REM sleep without atonia
- Electromyogram (EMG) : Chin (mentalis) EMG → normal REM sleep muscle atonia + absence of atonia in REM = RBD (REM sleep behavior disorder) + Lower limb EMG → periodic limb movements during sleep (PLMS) — repetitive leg jerks every 5–90 seconds + sleep disrupting
- Respiratory sensors nasal thermistor (airflow measurement) + nasal pressure sensor (PTAF - more sensitive for detecting hypopneas) + thoracic and abdominal belts (respiratory inductance plethysmography - respiratory effort measurement) + snoring microphone + apnea definition: airflow cessation ≥ 10 seconds + hypopnea definition: airflow reduction ≥ 30%% for ≥ 10 seconds with desaturation ≥ 3–4%% and/or arousal
- Pulse oximetry and ECG SpO₂ continuous by pulse oximeter + detects nocturnal desaturations + ODI (Oxygen Desaturation Index — number of desaturations ≥ 3 % or ≥ 4 % per hour of sleep) + total time spent below 90 % SpO₂ (T90) + 2-lead ECG → nocturnal arrhythmias + AV block associated with apnea + severe bradycardia during apnea
Indications for a full in-lab polysomnography
| Indication | Clinical justification | Alternative acceptable |
|---|---|---|
| SAOS - Clinical suspicion in adults with significant comorbidities | Heart failure + severe COPD + hypoventilation + morbid obesity (BMI > 40) + neuromuscular pathology + suspected central hypoventilation + doubtful or negative ambulatory test results but strong clinical suspicion persists | Ambulatory recording type III (4 channels or more - flow + effort + SpO₂ + ECG) acceptable if no comorbidities and isolated OSA suspected |
| Narcolepsy - clinical suspicion | Excessive daytime somnolence + suspected cataplexy + hypnagogic hallucinations + sleep paralysis + differential diagnosis with idiopathic hypersomnia + PSG is mandatory before MSLT (Multiple Sleep Latency Test) to rule out underlying OSAHS and confirm sufficient sleep duration | None—PSG + MSLT the following morning are mandatory for the diagnosis of narcolepsy according to ICSD-3 criteria + CSF hypocretin-1 measurement if cataplexy |
| REM Sleep Behavior Disorder (RBD) - Parasomnias | Complex motor behaviors during REM sleep (vocalization + crying + limb movements + falling out of bed) + often a predictor of synucleinopathy (Parkinson's + multiple system atrophy + Lewy body dementia) → PSG with extended EMG recording confirms the absence of REM atonia (REM sleep without atonia) | None - PSG with video EMG is required to confirm RBD and exclude nocturnal frontal epilepsy (similar picture) or OSA with violent arousals. |
| Suspected nocturnal epilepsy | Recurrent paroxysmal nocturnal events suggestive of epileptic seizures (nocturnal frontal lobe epilepsy) + PSG with extended EEG (epilepsy montage) + HD video → capture of ictal discharges and ictal behavior | Prolonged nighttime EEG video monitoring in neurology if epilepsy is strongly suspected |
| CPAP Titration (Severe OSA) | Manual titration of optimal CPAP pressure level by the sleep technologist in real-time + indicated if auto-CPAP is insufficient + anatomical and physiological complexity + associated hypoventilation | Ambulatory Auto-CPAP acceptable for most simple OSA |
| Restless legs syndrome + severe PMS | Precise quantification of the index of periodic limb movements during sleep (IMPM) + assessment of impact on sleep continuity + distinction from apnea-related arousals | Clinical diagnosis of RLS often sufficient (IRLSSG questionnaire) - PSG if diagnostic doubt or suspected associated OSA |
Sleep staging and normal architecture
- Sleep stages in normal adults : N1 (very light sleep — 5 to 10 % of sleep time) + N2 (light sleep — 45 to 55 % — most represented stage) + N3 (deep slow-wave sleep — 15 to 25 % — predominant in the first half of the night) + REM sleep (paradoxical sleep — 20 to 25 % — predominant in the second half of the night with increasingly longer cycles)
- Normal cyclic architecture: 90- to 120-minute cycles alternating between non-REM and REM sleep + 4 to 6 cycles per night + normal sleep latency < 20 minutes + normal first REM sleep latency 70 to 120 minutes + very short REM latency ((20 minutes or less) = SOREMP = suggestive of narcolepsy or severe sleep deprivation
- Quantitative parameters usually reported: total sleep time (TST) + sleep efficiency (TST / time in bed × 100 %— normal ≥ 85 % ) + sleep latency + first REM latency + percentage of each stage + arousal index (number of arousals per hour of sleep — normal < 5/h) + apnea-hypopnea index (AHI — normal < 5 events/hour of sleep)
Apnea-Hypopnea Index (AHI) — OSA Severity
- IAH normal < 5 events/hour of sleep + no intervention required
- Light SAOS: IAH 5 to 14 events/hour + CPAP treatment if symptomatic daytime sleepiness + or cardiovascular comorbidities + or resistant hypertension
- Moderate SAOS: AHI 15 to 29 events/hour + CPAP treatment recommended in almost all cases
- Severe SAOS: IAH ≥ 30 events/hour + mandatory CPAP treatment + contraindication to driving without treatment (SAAQ — legal obligations in Quebec) + restriction on high-risk occupations (pilots + professional drivers)
- Severe nocturnal hypoxemia: T90 > 10 % (total time spent below 90 % SpO₂) or minimal nocturnal desaturation < 80 % + indication for urgent treatment + complete cardiovascular assessment
ℹ️
In Quebec, access to full in-lab polysomnography (PSG) for sleep studies can involve waiting times of 6 to 24 months in the public sector. For the diagnosis of uncomplicated moderate-to-severe obstructive sleep apnea (OSA) in adults without significant comorbidities, ambulatory polysomnography (Type III at home - available in private clinics and some CLSCs) or nocturnal oximetry + questionnaires (Epworth + STOP-Bang) are valid alternatives that allow for rapid initiation of CPAP treatment without waiting for in-lab PSG. Clinique Omicron can direct patients to the fastest available resources based on their clinical profile.
Medical consultation recommended quickly
Consult a doctor quickly if a sleep disorder is accompanied by excessive daytime sleepiness with safety risks (driving + working with heavy machinery) + or by observed apneas by a partner with prolonged respiratory pauses + or by documented nocturnal desaturations at SpO₂ < 85 % + or by treatment-resistant high blood pressure — these situations require urgent assessment and priority investigation for severe OSAS.
For the prescription of nocturnal oximetry or ambulatory monitoring, referral to a sleep lab for a full PSG or to a sleep specialist pulmonologist, Clinique Omicron offers medical consultations at its service points in Quebec and via telemedicine. To make an appointment, visit cliniqueomicron.ca.
Consult at Clinique Omicron
Physicians and Nurse Practitioners (NPs) at Clinique Omicron evaluate patients with sleep disorders (snoring + apnea + daytime sleepiness + insomnia + abnormal nocturnal behaviors) using the Epworth questionnaire, STOP-Bang questionnaire, and a clinical examination. They prescribe nocturnal oximetry or ambulatory type III monitoring as the first diagnostic step, initiate CPAP treatment after confirming OSA, and refer to the sleep laboratory for a full PSG in complex cases (narcolepsy + parasomnias + nocturnal epilepsy + OSA with comorbidities). Consultations are available at multiple service points across Quebec and via telemedicine. To make an appointment, visit cliniqueomicron.ca.
The content of this page is provided for informational purposes only and does not substitute for the advice of a sleep specialist or pulmonologist. The interpretation of a polysomnography requires specialized training — results should always be integrated into the patient's clinical context to guide therapeutic decisions.
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