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

Polysomnogram (PSG)

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

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

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)

Sample PSG Results

Sleep Study Sample Report

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

Respiratory Events by Position

Sample Hypnogram

Dramatic OSA in REM

PSG: 120 sec Epoch

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

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

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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