Basics of Polysomnography Chitra Lal, MD, FCCP, FAASM Assistant professor of Medicine, Pulmonary, Critical Care and Sleep, MUSC, Charleston, SC
Basics of Polysomnography Continuous and simultaneous recording of several physiologic variables during sleep EEG EOG EMG ECG Snoring Thoracic and abdominal movements SaO2 Airflow
Polysomnogram Additional Channels : - End tidal Co2 (PetCo2) - Transcutaneous CO2 - PAP level - Esophageal pressure monitor - Additional EEG channels for nocturnal seizures - Video monitoring - Esophageal ph
Types of Sleep Studies Diagnostic PSG PAP titration study Split night study
Electroencephalography International 10-20 system (10% or 20% inter-electrode distance) Electrodes are identified by letters representing brain regions and a numeric subscript representing side of the body F is Frontal O is occipital C is central M is mastoid Odd # s are left side, even # s are right side, z is midline AASM recommends F4M1, C4M1 and O2M1
Electro-oculography(EOG) Cornea is positively charged Retina is negatively charged EOG measures the potential difference (PD) (dipole) between the two Positive voltage (downward deflection) is when the eye moves towards an electrode and vice-versa AASM recommends E1M2 and E2M2 E1 is 1 cm below the left outer canthus E2 is 1 cm above the right outer canthus Conjugate eye movements cause out-of-phase deflections
EMG (chin) 3 EMG leads : - midline and 1 cm above the inferior edge of the mandible - 2 cm to the right of midline and 2 cm below the inferior edge of the mandible - 2 cm to the left of midline and 2 cm below the inferior edge of the mandible 1 cm electrode distances for children Derivation consists of either electrode below the mandible referenced to the electrode above the mandible Additional masseter electrodes for Bruxism
ECG Single modified lead II : electrodes below right clavicle near sternum and over left lateral chest wall
Airflow Apneas are scored by Oronasal thermistor (recommended) or nasal air pressure transducer (alternative) Hypopneas are scored by nasal air pressure transducer(recommended) or Oronasal thermistor (alternative) Respiratory effort related arousals are scored by nasal air pressure transducer or respiratory effort
Airflow Oronasal thermistor measures temperature change with airflow, roughly quantitative measure Nasal pressure transducer measures subtle variations in airflow
Respiratory Effort Esophageal pressure monitoring (balloon measure, very uncomfortable, recommended by AASM) Surface diaphragmatic EMG Respiratory Inductance Plethysmography (RIP) : calibrated volumetric measure for chest and abdominal wall excursion (AASM recommended) Strain guages : use mercury, now banned in hospitals Effort belts : piezo-crystal sensors
Ventilation Pulse oximetry PetCo2 (end tidal CO2) or transcutaneous Co2 in children for alveolar hypoventilation Snoring is recorded with a microphone
EMG (anterior tibialis) Detects periodic limb movements of sleep (PLMS) Additional electrodes over the extensor digitorum communis to detect RBD
Interpretation of PSG 30 second periods or epochs Paper speed of 10 mm/second Original scoring criteria per Rechtshaffen & Kales (R & K), recently revised by AASM Majority of Epoch rule Each epoch is assigned a sleep stage
Wake Alpha rhythm over occipital region > 50% of epoch with eye closure, slow-rolling eye movements Open eyes wakefulness : beta rhythm, conjugate vertical eye blinks, reading eye movements High chin tone
Stages of Sleep N1 : Theta waves > 50% of epoch, slow-rolling eye movements, low chin tone, vertex waves (central region, < 0.5 seconds) N2 : K complexes and spindles, background theta rhythm, can have delta waves < 20% of epoch N3 : Delta waves > 20% of epoch REM sleep : REM s, lowest chin tone, saw-tooth waves, relatively low voltage, mixed frequency EEG
Stage N1 Alpha rhythm is attenuated and Theta waves >50% of the epoch If no alpha rhythm is generated, stage N1 if: - Vertex waves are present - EEG is 4-7 Hz frequency, and 1 Hz slower then the background rhythm in stage W - Slow eye movements
Stage N2 Score N2 (in absence of criteria for N3) if either/both occur in the first ½ of that epoch or in the last ½ of the previous epoch: - K complex without associated arousal - Sleep spindles Continue staging N2 for epochs with low-amplitude, mixed frequency EEG without K complexes/spindles, if they are preceded by epochs with K complexes without arousals/spindles
Stage N2 End stage N2 when 1 of the following occurs: - transition to stage W, N3 or R - arousal -major body movement followed by slow eye movements without non-arousal associated K complexes/spindles
Stage R Score R if ALL of the following are met: - Low-amplitude, mixed-frequency EEG - Low chin EMG tone - Rapid eye movements REM RULES: Continue staging R even in the absence of rapid eye movements, if EEG is low-amplitude, mixed frequency, no K/spindles, and low chin tone
Stage R Stop staging R if: - transition to W or N3 - in chin tone - arousal/major body movement followed by slow eye movements - non-arousal associated K complex/spindle occurs
Major Body Movement Movement or muscle artifact obscuring > ½ of the epoch, so that sleep stage cannot be determined If alpha for part of the epoch (even if < 1/2 of the epoch), stage it as W If no alpha is discernible, but W epoch precedes/follows it, stage it as W Otherwise, stage it as the epoch which follows it
Arousal Abrupt shift of EEG frequency, including alpha and/or frequencies > 16 Hz (not spindles) which last for 3 seconds and are preceded by 10 seconds of sleep Arousal from REM sleep also requires a concurrent in chin tone for 1 seconds
Arousal after respiratory event
Periodic Limb Movements of Sleep (PLMS) Significant leg movement (LM) definition: - Duration of LM between 0.5-10 seconds - 8 microvolts increase in EMG voltage above resting EMG PLM series: - 4 consecutive LM events - Duration between LM events between 5-90 seconds - if duration between LM events is < 5 seconds, count as 1 LM
Periodic Limb Movements of Sleep
Respiratory Rules Apneas are scored by oronasal thermistor Hypopneas are scored by nasal pressure transducer During PAP titration, use PAP device flow signal to score respiratory events Respiratory effort is scored by esophageal manometry (gold standard) or thoracoabdominal RIP belts
Hypopnea Peak signal excursion drops by 30% of pre-event baseline for 10 seconds with a 3% drop in oxygen saturation or arousal (current AASM recommended) Classification of hypopneas as obstructive or central is optional
Hypopnea Obstructive: - snoring - inspiratory flattening of flow signal - thoracoabdominal paradox Central: - absence of obstructive features
Respiratory Effort Related Arousal (RERA) Sequence of breaths lasting 10 seconds with increasing respiratory effort or decreasing inspiratory flow followed by an arousal, and does not meet criteria for apnea/hypopnea
Hypoventilation paco2 (or surrogate) to > 55 mm Hg for 10 minutes OR 10 mm Hg increase in paco2 (or surrogate) during sleep (compared to awake supine value) to > 50 mm Hg for 10 minutes
Cheyne-Stokes Breathing 3 consecutive central apneas and/or central hypopneas separated by crescendo-decrescendo breathing with a cycle length of 40 seconds OR 5 central apneas and/or central hypopneas per hour of sleep with crescendo-decrescendo breathing over 2 hours of monitoring
Cheyne-Stokes Breathing
Sleep Scoring Data Lights out clock time (hr:min) Lights on clock time (hr:min) Total Sleep Time (TST) Total Recording Time (TRT; lights out to lights on in min) Sleep latency (SL; lights out to first epoch of any stage of sleep) REM latency (sleep onset to first epoch of REM sleep in minutes)
Sleep Scoring Data Wake after sleep onset (WASO; TRT-SL-TST, in min) Percent sleep efficiency (TST/TRT X 100) Time in each stage in minutes Time in each stage/tst x 100 Arousal Index (ArI; # of arousals x 60/TST) Periodic limb movements of sleep index (PLMSI; PLMS x 60/TST) PLMS arousal index (PLMSArI; PLMS with arousals x 60/TST)
Sleep Scoring Data Apnea-Hypopnea Index (AHI; # of apneas + hypopneas x 60/TST) Respiratory Disturbance Index (RDI; RERA s + apneas + hypopneas x 60/TST)