Apnea load (total duration of apnoea events) and hypopnoea load (total duration of hypopnoea events) correlate better with the Epworth Sleepiness Scale (ESS), compared to the traditional Apnoea-Hypopnoea Index (AHI). (https://pubmed.ncbi.nlm.nih.gov/30019066/)

Study Summary: “Apnoeic and Hypopnoeic Load in Obstructive Sleep Apnoea: Correlation with Epworth Sleepiness Scale” (https://pubmed.ncbi.nlm.nih.gov/30019066/)

Objective:

To evaluate whether apnoea load (total duration of apnoea events) and hypopnoea load (total duration of hypopnoea events) correlate better with excessive daytime sleepiness (EDS), as measured by the Epworth Sleepiness Scale (ESS), compared to the traditional Apnoea-Hypopnoea Index (AHI).

Methods:

  • Study Design: Retrospective analysis of polysomnography (PSG) data from 821 patients with suspected obstructive sleep apnoea (OSA).
  • Inclusion Criteria:
  • Adults with AHI ≥5.
  • Underwent in-laboratory PSG.
  • Exclusion Criteria:
  • Medical or psychiatric conditions and medications affecting daytime sleepiness.
  • Previous diagnosis or treatment of OSA.
  • Other sleep disorders (e.g., restless leg syndrome).
  • Metrics Assessed:
  • ESS scores for EDS.
  • Apnoea and hypopnoea loads, AHI, sleep architecture parameters, and oxygen saturation indices.

The ranges of apnoea load and hypopnoea load were analyzed in the study to assess their correlation with the Epworth Sleepiness Scale (ESS) and their variation across obstructive sleep apnoea (OSA) severity levels. Here are the ranges based on the stratification of OSA severity:

1. Apnoea Load (Total Duration of Apnoea Events in Minutes):

  • Mild OSA (AHI 5–14.9):
    Mean ± SD: 4.2 ± 5.4 minutes
    Range: Typically lower compared to moderate and severe OSA.
  • Moderate OSA (AHI 15–29.9):
    Mean ± SD: 16.3 ± 18.8 minutes
    Range: Intermediate between mild and severe OSA.
  • Severe OSA (AHI ≥30):
    Mean ± SD: 86.6 ± 80.2 minutes
    Range: Significantly higher, indicating a much larger burden of prolonged apnoeic events.

2. Hypopnoea Load (Total Duration of Hypopnoea Events in Minutes):

  • Mild OSA (AHI 5–14.9):
    Mean ± SD: 29.5 ± 13.6 minutes
    Range: Lower hypopnoea burden compared to higher severity groups.
  • Moderate OSA (AHI 15–29.9):
    Mean ± SD: 55.3 ± 23.3 minutes
    Range: Increased hypopnoea load relative to mild OSA.
  • Severe OSA (AHI ≥30):
    Mean ± SD: 78.9 ± 47.5 minutes
    Range: The highest hypopnoea burden among the groups.

Key Observations:

  • Apnoea load increases significantly with OSA severity, particularly in severe OSA.
  • Hypopnoea load also increases with severity but does not correlate as strongly with excessive daytime sleepiness (EDS) as apnoea load.
  • Severe OSA patients exhibit the highest combined apnoea and hypopnoea loads, indicating a greater total respiratory event burden.

These ranges underscore the importance of considering event duration alongside event frequency (AHI) for a more comprehensive assessment of OSA severity.

Key Results:

  1. AHI vs. ESS:
  • No significant correlation was found between AHI and ESS (P = 0.584), questioning AHI’s utility as a predictor of EDS.
  1. Apnoea Load:
  • A positive correlation was observed between apnoea load and ESS (P = 0.003), particularly in patients with severe OSA.
  1. Hypopnoea Load:
  • Hypopnoea load did not significantly correlate with ESS (P = 0.162).
  1. Oxygen Saturation:
  • Minimum SpOâ‚‚ negatively correlated with ESS (P = 0.041).
  • Time spent with SpOâ‚‚ <85% or <90% was positively correlated with ESS in univariate analyses but not in multivariate models.
  1. Sleep Architecture:
  • Increased durations of Stage 1 and REM sleep were independently associated with higher ESS scores in multivariate analyses.
  • Total sleep time and NREM sleep correlated positively with ESS in univariate analyses.
  1. Demographics:
  • Younger patients demonstrated higher ESS scores (P < 0.001).
  • Severe OSA was associated with higher apnoea and hypopnoea loads, as well as worse oxygen saturation.

Conclusions:

  • AHI does not adequately predict EDS in OSA patients.
  • Apnoea load, reflecting the cumulative duration of apnoeas, is a better predictor of EDS, particularly in severe OSA.
  • Sleep architecture, especially increased Stage 1 and REM sleep, and oxygen desaturation also influence ESS scores.
  • Incorporating metrics like apnoea load and oxygen saturation into OSA severity assessments could improve predictions of disease burden and patient outcomes.

Clinical Implications:

  • ESS, combined with objective measures such as apnoea load, can better guide clinicians in evaluating and managing OSA-related daytime sleepiness.
  • The findings highlight the need to move beyond AHI as the sole metric for OSA severity.

Limitations:

  • Retrospective design with potential selection bias.
  • ESS is subjective and may not fully capture EDS severity.
  • Study population consisted of Asian patients, limiting generalizability.

Future Directions:

  • Explore the role of oxidative stress and genetic factors in OSA-related EDS.
  • Investigate the impact of integrating apnoea load and oxygen desaturation indices into clinical guidelines for OSA severity classification.