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Original research
Night-to-night variability of respiratory events in obstructive sleep apnoea: a systematic review and meta-analysis
  1. Maurice Roeder1,
  2. Matteo Bradicich1,
  3. Esther Irene Schwarz1,
  4. Sira Thiel1,
  5. Thomas Gaisl1,
  6. Ulrike Held2,
  7. Malcolm Kohler1
  1. 1 Department of Pulmonology, University Hospital Zurich, Zurich, Switzerland
  2. 2 Epidemiology, Biostatistics and Prevention Institute, University of Zurich, Zurich, Switzerland
  1. Correspondence to Prof. Dr. Malcolm Kohler, Department of Pulmonology, University Hospital Zurich, Zurich, Switzerland; malcolm.kohler{at}


Background It is current practice to use a single diagnostic sleep study in the diagnostic workup of obstructive sleep apnoea (OSA). However, a relevant night-to-night variability (NtNV) of respiratory events has been reported.

Methods We evaluated the NtNV of respiratory events in adults with suspected or already diagnosed OSA who underwent more than one diagnostic sleep study. Data sources were PubMed, Cochrane and Embase up to 23 January 2019. Random-effects models were used for evidence synthesis. For moderator analysis, mixed-effects regression analysis was performed. The study was registered with PROSPERO (CRD42019135277).

Results Of 2143 identified papers, 24 studies, comprising 3250 participants, were included. The mean Apnoea-Hypopnoea Index (AHI) difference between the first and second night was −1.70/hour (95% CI −3.61 to 0.02). REM time differences (first to second night) were significantly positive associated with differences in mean AHI (β coefficient 0.262 (95% CI 0.096 to 0.428). On average, 41% (95% CI 27% to 57%) of all participants showed changes of respiratory events >10/hour from night to night. Furthermore, 49% (95% CI 32% to 65%) of participants changed OSA severity class (severity thresholds at 5/hour, 15/hour and 30/hour) at least once in sequential sleep studies. Depending on the diagnostic threshold (5/hour, 10/hour or 15/hour), on average 12% (95% CI 9% to 15%), 12% (95% CI 8% to 19%) and 10% (95% CI 8% to 13%) of patients would have been missed during the first night due to single night testing.

Conclusion While there was no significant difference between mean AHI in two sequential study nights on a group level, there was a remarkable intraindividual NtNV of respiratory events, leading to misdiagnosis and misclassification of patients with suspected OSA.

  • sleep apnoea

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  • MR and MB contributed equally.

  • Contributors MR and MK conceived of the idea for this review. MR, EIS, TG and UH wrote the protocol, MR and MB performed the data extraction. TG and ST did the quality assessment. UH, MR and MB did the statistical analysis. MR, MB, EIS, TG, ST and MK interpreted the statistical results. MR and MB wrote the first draft of the manuscript. All authors revised and approved the final manuscript. MR und MB shared the first authorship.

  • Funding This project was supported by a grant of 'Lunge Zürich'.

  • Disclaimer The funding source had no role in the design, execution, analyses, interpretation of the data, or decision to submit results.

  • Competing interests MK and TG report advisory fees from Bayer.

  • Patient consent for publication Not required.

  • Provenance and peer review Not commissioned; externally peer reviewed.

  • Data availability statement Data are available on reasonable request. All data relevant to the study are included in the article or uploaded as supplementary information. Data are provided in the manuscript and in the online supplementary tables. Further data are available on reasonable request.