POLYSOMNOGRAPHY & EEG ACTIVATION METHODS

SLEEP STUDY AND UNCONVENTIONAL EEGs

DR. PIYUSH OJHADM RESIDENT

DEPARTMENT OF NEUROLOGYGOVT MEDICAL COLLEGE, KOTA

POLYSOMNOGRAPHY

• Introduction• Indications• Patient evaluation and instructions• Components• Derived Information• Types• Limitation• Summmary

INTRODUCTION

• Term “Polysomnography” was proposed by Holland ,Dement and Raynal (1974).

• The most commonly used test in the diagnosis of obstructive sleep apnea syndrome (OSAS).

• Consists of a simultaneous recording of multiple physiologic parameters related to sleep and wakefulness.

INDICATIONS FOR POLYSOMNOGRAPHY

• Sleep related breathing disorders• CPAP titration in OSA• Assessment of treatment results- OSA• Sleep related behavioral disorders• Atypical or unusual parasomnias• Narcolepsy• Neuromuscular disorder & sleep related symptoms• Paroxysmal arousal or seizure phenomenon• Periodic Leg Movements of Sleep• Parasomnias not responding to conventional therapy

Initial Assessment• Detailed medical & psychiatric history• Medication, smoking, alcohol, activities on that day

Assessment of sleep:• Sleep history for the last 24 hrs.

Sleep scoring systems1. Stanford Sleepiness scale2. Epworth Sleepiness scale3. Pittsburgh Sleep Quality Index (PSQI)

RECORDING ROOM• The study patient and the monitoring apparatus and

technologist are housed in adjacent rooms.• Recording room should be as homely and comfortable as

possible.

• It should be sound-proofed and air-conditioned.• Intercom system to interact with the patient.

• Rheostatically controlled lighting• Toilet and restroom

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INSTRUCTION TO THE PATIENT• Reporting time: 1 hour prior to the usual time of sleep.• A prior visit to familiarize with the lab is useful.• Patient should have had a relaxed day, without daytime

sleep.• Headwash, adequate food is recommended.• Abstain from caffeine in the afternoon and evening of

the day on which PSG is planned• Avoid alcohol on the day of PSG• Avoid strenuous exercise on the day of the PSG.

INSTRUCTION TO THE PATIENT• Continue their usual medications on the night of the

PSG, including sleep aids.• The medications should be recorded by the technician so

that the results can be optimally interpreted.• For patients who have a history of insomnia, especially

when sleeping in a new environment, Zolpidem may be prescribed.

• Avoid stimulants, including medications for narcolepsy.• Avoid naps on the day of the sleep study.

COMPONENTS OF POLYSOMNOGRAPHY

ELECTROENCEPHALOGRAPHY (EEG)

• To distinguish between wakefulness and the various stages of sleep

• A minimum of three channels representing the right frontal, central, and occipital electrodes referenced to the contralateral mastoid electrode is recommended (2007 AASM Manual for the Scoring of Sleep and Associated Events)

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ELECTRO-OCULOGRAPHY (EOG)

• Two recommended electrodes are labeled E1 (1 cm below the left outer canthus) and E2 (placed 1 cm above the right outer canthus), both referenced to the right mastoid.

• This allows simultaneous recording of both vertical eye movements (such as blinking) and horizontal eye movements (both slow and rapid).

• Documents the onset of rapid eye movement (REM) sleep, and notes the presence of slow-rolling eye movements that usually accompany the onset of sleep.

ELECTROMYOGRAPHY (EMG)• Help to determine sleep stage• Help to diagnose and classify a variety of parasomnias

• Minimum components are chin EMG channels recording activity from the mentalis and submental muscles (the mylohyoid and anterior belly of the digastric) and bilateral leg EMG channels recording activity from the tibialis anterior muscles.

• Tonic EMG level in axial muscles usually decreases from wakefulness through stages 1, 2, 3, and 4 of NREM sleep, and is normally absent in REM sleep

EMG MONITORING

Utility of limb EMG:

• Periodic limb movements in sleep.• Restless leg syndrome.• Other movement disorders.• To document the hand and arm gestures of REM

sleep behavior disorder.• Record convulsive movements during nocturnal

epileptic seizures.

RESPIRATORY MONITORING

• Upper airway airflow• Thoracoabdominal movement.• Endoesophageal (intrathoracic) pressure

recording.• Snoring Monitors.• Indirect Arterial Blood Gas Monitoring.

UPPER AIRWAY AIRFLOW

• Oronasal thermal devices (thermistors or thermocouples) or nasal cannula–pressure transducers

• Thermistor/ thermocouple: placed between the nose and mouth is commonly used to monitor airflow by detecting changes in temperature

• Thermistor consisting of wires records changes in electrical resistance

• Thermocouples consisting of dissimilar metals (e.G., Copper and constantan) register changes in voltage that result from temperature variation

UPPER AIRWAY AIRFLOW

• Nasal prongs connected to a pressure transducer detect inspiratory flow and may be the most accurate method to identify subtle inspiratory flow limitation – hypopneas

• An important limitation of nasal pressure transducers is that they cannot detect mouth breathing. To overcome this limitation, a thermistor is usually added.

• Nasal pressure transducers are necessary for the diagnosis of hypopneas and thermistors are necessary for the diagnosis of apneas

THORACOABDOMINAL MOVEMENTS

Respiratory Inductive Plethysmography:• Measures changes in thoracoabdominal cross-

sectional areas, and the sum of these two compartments is proportional to airflow

• Sensors are two wire coils, one placed around the chest and the other around the abdomen.

• A change in mean cross-sectional coil area produces a proportional variation in coil inductance, which is converted into a voltage change by a variable frequency oscillator.

SNORING MONITORS

• Although snoring can be monitored by placing a miniature microphone on the patient’s neck, there is no accepted grading system to quantify the intensity of this parameter.

• In practice the technologist’s notations as the study is being recorded, as well as the polysomnographer’s review of the audio as the study is being read, provide a better estimation of the degree of snoring

INTRATHORACIC PRESSURE MONITORING

Endoesophageal pressure probe:– Most sensitive detection of heightened respiratory effort.– An endoesophageal tube is passed nasally till the probe is

about 5 cm above the esophageal-gastric junction.– Measures increases in intrathoracic negative pressure to

overcome increased upper airway resistance.• Gold standard for measuring respiratory effort• Not a routine practice , because of patient

discomfort and the technical skill required

CAPNOGRAPHY

• Capnography, or end-tidal CO2 (ETCO2), monitoring detects the expired carbon dioxide (CO2) level, which closely approximates intra-alveolar CO2.

• An infrared analyzer over the nose and mouth detects CO2 in the expired air, which qualitatively measures the airflow

• Costly and therefore not used in most laboratories

ABG

• An alternative to capnography is measurement of the (Paco2) in the morning after their sleep study to be compared to their waking Paco2

• Adults who have an increase in their paco2 in sleep by 10 mm hg or more compared to an awake supine paco2 have sleeprelated hypoventilation

OXYGEN SATURATION

• Continuous oxygen saturation monitoring by finger pulse oximetry is routine .

• PSG reports mention the time the patient spent with an SpO2 below 90%.

ELECTROCARDIOGRAM(ECG)

• ECG abnormalities in sleep apnea patients:1. Marked sinus arrhythmia.2. Extra systoles.3. Prolonged asystolic episodes.4. Atrial or ventricular fibrillation.5. Nocturnal angina may show ST segment

deviation.

BODY POSITION

• Some patients only have abnormalities when sleeping in certain positions. Therefore, body position (eg, supine, left lateral, right lateral, prone) is monitored throughout the test using a position sensor and/or video monitor.

OPTIONAL PARAMETERS1)Esophageal pH• Gastro-esophageal reflux of acidic stomach contents into the

lower esophagus may cause insomnia.• pH probe is introduced nasally and swallowed to about 5 cm

above the esophageal sphincter.2)Penile Tumescence• Psychogenic Vs organic causes of impotence.• In normal adult men, penile tumescence occurs during REM

sleep• Psychogenic cases: Normal REM sleep-related erections.3)Core Body Temperature

INTERPRETATION OF PSG• Total sleep time – The total sleep time (TST) is the total duration

of light sleep (stages N1 and N2), deep sleep (stage N3), and rapid eye movement (REM) sleep

• Sleep efficiency – Sleep efficiency (SE) is the TST divided by the total recording time (ie, the time in bed).

• Sleep stage percentage – The sleep stage percentage (SSP) for a particular sleep stage is the duration of that sleep stage divided by the TST.

• Sleep stage latency – The latency to any sleep stage is the duration from sleep onset to the initiation of that sleep stage.

• Arousals – Arousals range from full awakenings to three-second transient electroencephalography (EEG) shifts to a lighter stage of sleep (alpha, theta, and/or frequencies greater than 16 Hz, but not sleep spindles, with at least 10 seconds of stable sleep preceding the change).

• Arousals are generally counted and then divided by the TST to give the number of arousals per hour of sleep (ie, arousal index).

• Apnea is defined by the American Academy of Sleep Medicine (AASM) as the cessation of airflow for at least 10 seconds.

• Hypopnea is defined as decrease in airflow of ≥30 % (by a valid measure of airflow) lasting ≥10 s, associated with either ≥3 % desaturation from the pre-event baseline or an arousal

• Respiratory effort–related arousal (RERA) is an event characterized by increasing respiratory effort for 10

seconds or longer leading to an arousal from sleep but one that does not fulfill the criteria for a hypopnea or apnea.

INDICES FOR SLEEP APNEA SYNDROMES

• Apnea-hypopnea index (AHI) The AHI is defined as the average number of

episodes of apnea and hypopnea per hour.• Respiratory disturbance index (RDI) Defined as the average number of respiratory

disturbances (obstructive apneas, hypopneas, and respiratory event–related arousals [RERAs]) per hour.

AASM CRITERIA FOR OSASEVERITY AHI

Normal < 5

Mild 5 -15

Moderate 15 - 30

Severe > 30

SLEEP RELATED BREATHING DISORDERS BASED ON PSG

SRBD AHI Arousal Index

Snoring Daytime alertness

Simple Snoring

<5 <10 + Normal

UARS <10 Often >15 +/- Impaired

OSAS-Mild 5-15 5-20 + Mild impairment

OSAS- Moderate

15-30 10-30 + Moderate impairment

OSAS- Severe

>30 >20 ++ Severe impairment

CSAS >5 Central Apnoea

>10 +/- Variable

TYPES OF PSG

• Four types based on the number of parameters they measure and the degree of attendance required.

• Level 1 devices - Traditional attended in-laboratory PSGs

• Level 2 through 4 refer to home studies recorded by portable devices with progressively fewer channels measuring progressively fewer parameters

• Level II devices require a minimum of seven channels, including EEG,EOG, chin EMG, ECG, oximetry, airflow, and respiratory effort channels. Thus they permit sleep scoring.

• Level III device: This device has a minimum of 4 channels, including ventilation or airflow (at least 2 channels of respiratory movement or airflow), heart rate or ECG, and oxygen saturation.

• Level IV device: This type of device does not meet requirements for other types, and many measure only 1-2 parameters (eg, oxygen saturation or airflow).

SPLIT NIGHT STUDIES

• Diagnosis of OSA is established during the first portion of the study and the amount of positive airway pressure that is necessary to prevent upper airway collapse during sleep is determined during the remaining portion.

LIMITATIONS OF PSG STUDY

– First Night Effect:• Reduced sleep efficiency.• Increased awakenings and arousals.• Prolonged sleep and REM latency.• Decreased percentage of REM and slow-wave sleep.• Increased percentage of light sleep.

– Technology, technician, technique dependant.– Episodic disorders may be missed: eg seizures,

parasomnias.– Night- to- night variability: eg in case of apnea.

• VARIABILITY :– Night to night variability makes it possible for a

single study to underestimate the severity of OSA– Nasal patency, body position, or disruptive

environmental factors may all be important factors in producing such variability.

– Therefore, it is reasonable to repeat the baseline PSG if there is a strong clinical suspicion for OSA

CONCLUSION

• Attended, in-laboratory polysomnography (PSG) is considered the gold standard diagnostic test for obstructive sleep apnea (OSA)

• Diagnostic evaluation of suspected OSA, titration of positive airway pressure therapy, and assessment of the effectiveness of therapy are the most common indications for PSG.

UNCONVENTIONAL EEGs

• It is used to increase the yield of EEG.– Hyperventilation– Photic stimulation– Sleep– Sleep deprivation– Special forms of stimulus– Drug activation– Drug suppression

HYPERVENTILATION• Deep and regular respiration at a rate of about 20/minute for

about 2 to 4 minutes.• In adults Hyperventilation will cause an air exchange of about

20-50 L/min and a drop in PCO2 by approx 4-7 mm Hg.• Hypocarbia leads to Cerebral vasoconstriction and decreased

O2 and glucose supply to brain.• In children blowing game or an instrument is used.• Patient may feel light headedness, tingling, numbness and

rarely tetany.• EEG recorded 1min prior, during and 2 min after

hyperventilation.• Hyperventilation response is usually recorded during eye

closure.

• Characteristic EEG response: fluctuating increase of bilaterally synchronous theta activity and slowing of alpha and beta rhythms.

• Delta activity:– Frontal location in adults.– Posteriorly located in children.

• Effect is marked in childhood.• Decreased response in advanced age due to

decreased reactivity of cerebral vasculature to hypocarbia.

• Lack of response is not abnormal.• Sleep induced changes can follow.

• CONTRAINDICATIONS :-– Underlying respiratory or cardiac diseases.– Cerebrovascular insufficiency.– Raised intracranial pressure.– Old age above 65.– Lack of medical approval.

Hyperventilation induced brief absence with high voltage generalized 3 Hz spike wave discharge.

INTERMITTENT PHOTIC STIMULATION

• Activities following a series of regular light flashes.

• It is done to:– Observe the response.– Observe symmetry.– To precipitate photo sensitive seizure.– To observe suppression of preexisting EEG activity.

• Stroboscope is used for IPS.

• The lamp is placed 30cm in front of the patient.• Maximum intensity .4 Joules• Gird or grating pattern can enhance the ability.• Patient should fix at the lamp.• Recordings obtained with eyes open and closed.• Bickford protocol.– Flashes are given at frequency of 1, 3, 6, 9, 10, 15, 20 and

30Hz in trains of 5 sec duration in a room with rdduced illumination with eyes closed and open.

• Three pattern's of response

PHOTIC DRIVING RESPONSE (PDR)• Physiologic response consisting of rhythmic activity elicited over

the posterior regions of the head by IPS frequencies of about 5-30 Hz.

• Term should be limited to activity time locked to stimulus and of frequency identical or harmonically related to stimulus frequency.

• As a rule PDR is found over posterior regions.• In infants, PDR can be elicited a few hours after birth, but remains

small upto 6 years age.• In older children, PDR become larger , particularly at low

frequency.• Children and older persons have higher amplitude than adults.

PHOTIC DRIVING RESPONSE (PDR)• Regardless of age, an exaggerated PDR to low flash

frequencies (0.5-3 Hz) usually signifies acute or subacute neuronal dysfunction ( eg MELAS, late infantile form of ceroid lipofuscinosis)

• Large positive occipital sharp transients of sleep (POSTS) in response to scanning a complex pattern are predictive of a prominent PDR.

• Destructive cortical lesion – unilateral PDR depression.• Irritative lesions – increased PDR on the side of lesion.

PHOTIC DRIVING RESPONSE (PDR)

• Very low voltage or absence of PDR is of little diagnostic significance as some normal persons are not responsive to IPS.

• High amplitude PDR elicited by flickering dot pattern and red flicker stimuli in adult patient suggests occipital lobe disturbance.

• Augmented response : psychiatric illness.

PHOTOMYOCLONIC / PHOTOMYOGENIC RESPONSE

• Characterized by brief repetitive muscle spikes over anterior regions of the head.

• Often increase gradually in amplitude as stimulation continues and cease promptly when the stimulus is withdrawn.

• Associated with eyelid flutter and sometimes with discrete jerking, mostly involving musculature of the face and head.

• Time locked to stimulus.• Most effective triggering by flash frequency of 12 – 18Hz, eyes

closed.• Disappears on eye opening• Little clinical significance.• Enhanced by alcohol withdrawal, barbiturate and other sedative

withdrawal.

PHOTOPAROXYSMAL / PHOTOCONVULSIVE RESPONSE

• Response to IPS characterized by spike and wave or multi-spike and wave that are bilaterally symmetric, synchronous, generalized and outlasting the stimulus by a few seconds.

• See both eye open> closed.• Most commonly induced by flash frequency of 15Hz IPS with

eyes closed or 20Hz IPS eyes open.• There can be associated Loss of consciousness and brief jerks

of muscles of the body predominantly upper limbs & head.• Significant when response outlasts stimulus.• Seen in 2.8% patients referred for EEG

– Commonly in absence and GTCS.

• PPR may be a familial trait.• Those with PPR are susceptible to convulsion.• Four types of PPR seen

1. Spikes with occipital rhythm.2. Parieto-occipital spikes with biphasic slow waves.3. Parieto-occipital spikes with biphasic slow waves

spreading frontally.4. Generalized spikes and waves or poly spikes and waves.

• Type IV response is more suggestive of photosensitivity.

• PPR without history of seizure: metabolic or drug withdrawal.

• Other responses in IPS:– Posterior high amplitude symmetrical discharges

at low IPS rates: CJD, PME, diffuse encephalopathy's.

– High amplitude spikes at low IPS rates are seen in NCL

SLEEP ACTIVATION• Done by over night sleep deprivation or recording

during natural sleep.• Chloral hydrate can be used.

– 500 to 1000 mg PO 30 to 60 min before procedure.• To induce paroxysmal activity during sleep in epileptic

patients.– In partial seizures occur during drowsiness and light sleep.– In generalized seizures during deep sleep.– REM sleep discharges.

• Various sleep rhythms may not appear or asymmetric.

SLEEP DEPRIVATION

• Overnight sleep deprivation.• EEG recorded as patient falls asleep.• Focal epileptiform discharges may appear.• Yield enhanced by about 40%.

SPECIAL STIMULUS ACTIVATION

• Visual Stimulation: Used for testing IPS sensitive patients with a history of seizures during watching TV.– Also used to induce patients with pattern sensitive epilepsy

• Auditory stimulation: rarely used– Used in seizures due to primary auditory coretx

abnormality.

• Others:– Olfactory– Vegetative stimuli

DRUG ACTIVATION

• Drugs are used to activate epileptiform discharges.– Hypoglycemic agents(tolbutamide), seizure producing

drugs like pentylene tetrazole, bemegride• Dangerous procedure and should be under taken

with caution.• Can be used with IPS– High incidence of activation in normal subjects.– Irrelevant findings.

• May be useful in epilepsy surgery.

DRUG SUPPRESSION

• Focal epileptiform discharges may get obscured due to secondary generalized discharges in partial epilepsy.

• Can be suppressed by diazepam.– 1-2mg/min up to a total of 10 mg

• Unmasks focal discharges.• Avoid large doses as it may totally abolish

epileptiform discharges.• Watch for respiratory depression.

SUBDURAL ELECTRODE CORTICOGRAPHY

• Scalp electrode has limitations in its spatiotemporal resolution.

• Cortical interictal spikes are usually hetrogenous in their source location,area,synchrony, and amplitude.

• Only a few of these cortical spikes are associated with scalp recognizable potentials.

• Additionally, different cerebral source configuration can generate a similar distribution of scalp voltage.

• Also scalp ictal rhythms typically reflect propogation and recruitment, rather the location of seizure onset.

• So false localization is common in scalp EEG.

• So scalp EEG is used simply as a screening tool to select those requiring intracranial recordings or to exclude certain patients from further surgical evaluation.

• Identifying the seizure onset zone on intracranial EEG has become the cornerstone for localizing the epileptic foci.

• Subdural and or Depth Electrode are commonly used in this task of precisely localizing the epileptogenic foci.

• Subdural electrode can determine the extent of an epileptogenic foci for guiding tailored surgical resection.

• Subdural electrode are well adapted for cortical mapping, that is, electrical stimulation to localize motor,sensory and/or language cortex.

• Disadvantage – both implantation and removal requires major surgery (craniotomy) and these electrodes cannot localize seizure foci in deep-brain structures.

ELECTRODE PLACEMENT FOR SUBDURAL EEG

INTERICTAL SUBDURAL EEG SHOWING SPIKES INDEPENDENTLY ARISING FROM LEFT MESIAL AND NEOCORTICAL TEMPORAL LOBE AS WELL AS RIGHT

ANTERIOR MESIAL AND NEOCORTICAL REGIONS

DEPTH ELECTRODE EEG• Depth electrode are commonly used to identify deep

epileptogenic foci such as in amygdala, hippocampus, insula and sulcal cortex.

• They are commonly place with streotactic and/or neuronavigation guidance through small burr holes.

• Although a more technically challenging procedure, it is better tolerated by patients and has lesse risks for morbidity.

• The electrodes can be easily removed at bedside without significant discomfort.

• Disadvantage – not suited for functional mapping and provide limited sampling of neocortex compared to subdural electrodes.

THANK YOU

REFERENCES

• Niedermeyer’s textbook of Electroencephalography 6th edition

• The Epilepsies : Seizures,Syndromes and Management by C P Panayiotopoulos

• Current practice of clinical Electroencephalography by John S Ebersole 4th edition

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