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Interpreting Sleep Study Reports:

A Primer for Pulmonary Fellows

By Martha E. Billings, MD MSc
for the Sleep Education for Pulmonary
Fellows and Practitioners, SRN ATS Committee


Obstructive Sleep Apnea

  • Obstructive sleep apnea: repeated closure or narrowing of upper airway reducing airflow
  • Apnea: total cessation of air flow for 10 sec
  • Hypopnea: 10 sec of reduced air flow
  • Obstructive respiratory events are associated with snoring, thoracoabdomnial paradox & increasing effort
breathing
AASM Scoring Manual Version 2.1, 2014

Polysomnogram (PSG)

figure2

Scoring Criteria: Respiratory Events

  • Hypopnea definition
  • ↓ flow ≥ 30% from baseline for at least 10 seconds
  • 1A. (AASM) with 3% O2 desaturation OR arousal
    • Requires EEG monitoring
  • 1B. (CMS) with 4% O2 desaturation
  • Amenable to portable studies
  • Respiratory Effort Related Arousal (RERA)
  • Flattening of inspiratory portion of nasal pressure (or PAP flow) with increasing respiratory effort leading to arousal
  • No associated desaturation
  • Requires EEG monitoring

AASM Scoring Manual Version 2.1, 2014

Apnea Hypopnea Index

AHI = (# apneas + # hypopneas) / sleep hours

  • AHI < 5 normal
  • AHI 5 – 15 mild
  • AHI 15 – 30 moderate
  • AHI > 30 severe

RDI = (# apneas + # hypopneas + # RERAs) / sleep hours

  • Can be large difference in AHI vs. RDI if young, thin patient who is less likely to desaturate by 4% with events
  • Treatment not covered by Medicare if AHI < 5 but some insurances accept RDI >5 (with AHI < 5) with symptoms

PSG Epoch: Obstructive Apneas

epoch

In-lab PSG Data

Respiratory Data:

  • # Central, obstructive apneas, hypopneas & RERAs

    • AHI & RDI by position and sleep stage
    • Central apnea index & if Cheyne-Stokes pattern
  • Oximetry:
    • Oxygen Desaturation Index
    • Mean O2 saturation & nadir
  • Hypoxemic burden
    • Cumulative % of sleep time spent under 90%

EEGData:

Sleep efficiency & latency

  • Normal 80% efficient
  • Latency < 30 min, REM latency 60-120 min

Sleep stages & architecture

  • Normal  about 5% stage N1, 50% N2, 20% N3 (slow wave sleep) and 20-25% REM

Arousal Index (AI): sleep disruption

  • Normal AI < 10-25 (large variation by age)

Norms are all age dependent

  • in general less REM & SWS, more arousals, WASO and lower sleep efficiency as age

EEG abnormalities

  • Epileptiform activity, alpha intrusion

Sleep Architecture Over Lifespan

sleep-architecture

Ohayon MM, Carskadon MA, Guilleminault C, Vitiello MV. Meta-analysis of quantitative sleep parameters from childhood to old age in healthy individuals: developing normative sleep values across the human lifespan. Sleep 2004;27(7):1255-73

EMG Data & Video

Limb Movements

  • periodic limb movements index in wake & sleep
    • Normal PLMI < 15 adults
  • Movements during REM (loss of atonia)

Parasomnias

  • Sleep walking, talking
  • Bruxism
  • REM sleep behavior disorder

Classic OSA (300 sec)

classic osa

Sample PSG Results

psg-results

Sleep Study Sample Report

eeg-data

Sample PSG Results: OSA

Respiratory Data:

  • Apnea Hypopnea Index: AHI 17
    • 12 obstructive apneas, 45 hypopneas
    • RERA index 34
  • Oxygenation Desaturation Index: ODI 13
    • Nadir O2Saturation: 86%
    • Hypoxemic Burden: 13% of study O2 sat < 90%
  • Most severe supine, REM sleep (AHI 53)
  • Total RDI: 55

Sample PSG Report

events by sleep

Respiratory Events by Position

respiratory events

Sample Hypnogram

sample hypnogram

Dramatic OSA in REM

Dramatic OSA

PSG: 120 sec Epoch

  • Obstructive hypopneas/ RERAs with clear arousals but not consistent desaturation

PSG 120

Home Sleep Study (OCST)

  • Respiratory data only (estimated AHI, ODI) calculated from recording time
    • Underestimates AHI as recording time > time asleep
    • Problematic if insomnia
  • No EEG to determine sleep or arousal
    • No arousal associated hypopneas scored
    • No respiratory effort related arousals (RERAs)
    • No information by sleep stage (REM/NREM or if asleep)
  • Higher rates of technical failure
  • Appropriate for high likelihood OSA & no other sleep disorders or respiratory/cardiac disease

Home Study Tracing

Home Study

Sample OCST Results

  • Total recording time: 423 minutes
  • Supine sleep: 34%
  • AHI 8.4
    • 3 obstructive apneas, 2 central apneas
  • Oximetry
    • ODI 7
    • Nadir saturation 87%, mean 94%
  • Same patient as in sample PSG but lower AHI estimated b/c of poor sleep efficiency & less REM

Summary

  • In lab PSG provides details regarding EEG, EMG to give more complete evaluation of sleep disorder
  • When interpreting sleep study results, remember to consider:
    • % supine, REM sleep captured
    • AHI often underestimated in OCST
    • RDI vs. AHI & hypopnea criteria used

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Last Reviewed: June 2016