Abstract
Purpose
Recently, there has been a debate about the rules used to score hypopnea events. The purpose of this study was to examine the effect of different oxygen desaturation threshold (ODT) levels on the apnea-hypopnea index (AHI) and on a recently introduced parameter, adjusted AHI. Adjusted AHI incorporates the severity of individual breathing cessation events. We also aimed to clarify the impact of the different ODT levels on the current classification of obstructive sleep apnea (OSA) severity.
Methods
Ambulatory polygraphic recordings of 68 patients (19 F/49 M, median age 53.2 years, AHI ≥5) were analyzed retrospectively. Hypopneas were defined as ≥30 % drop in airflow for ≥10 s associated with ≥2 % oxygen desaturation (ODT2%), and after that, using stricter ODT criteria (ODT3%–ODT8%).
Results
Compared to ODT4%, the ODT3% resulted in 5.6 events/h higher median conventional AHI, but only 1.5 events/h higher median adjusted AHI. A significant rearrangement of patients between the clinical severity categories took place when using different ODTs. When assessing with ODT3% instead of ODT4%, the portion of the patients with moderate or severe OSA (AHI ≥15) raised from 29.4 to 73.5 % using conventional AHI, but only marginally, i.e., from 73.5 to 77.9 %, using the adjusted AHI.
Conclusions
The conventional AHI was found to be susceptible even to minor changes in ODT level which may lead to substantial variability in AHI-based classification of disease severity. Since the adjusted AHI comprises information on severity of individual breathing cessations, it reduces the variability related to ODT levels used in hypopnea scoring and can increase the accuracy of estimation of OSA severity.
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Acknowledgments
This study was financially supported by the Kuopio University Hospital (VTR-funding, projects 5041732, 5041733, 5041748) and Seinäjoki Central Hospital (VTRfunding, projects 3040 and 3114). K. Myllymaa is supported by the Finnish Cultural Foundation of Northern Savo and Finnish Brain Foundation.
Ethical statement
The study protocol was reviewed by the Research Ethics Committee of the Hospital District of Northern Savo, Kuopio, Finland (favorable opinion 127/2004). The patients were given both oral and written information about the study protocol, and they provided a signed informed consent.
Conflict of interest
The authors declare that they have no conflict of interest.
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Sami Myllymaa and Katja Myllymaa contributed equally to the paper
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Myllymaa, S., Myllymaa, K., Kupari, S. et al. Effect of different oxygen desaturation threshold levels on hypopnea scoring and classification of severity of sleep apnea. Sleep Breath 19, 947–954 (2015). https://doi.org/10.1007/s11325-015-1118-x
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DOI: https://doi.org/10.1007/s11325-015-1118-x