title: Effect of different oxygen desaturation threshold levels on hypopnea scoring and classification of severity of sleep apnea.
abstract: OBJECTIVE
  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.
authors.affiliation: Department of Clinical Neurophysiology, Kuopio University Hospital, PO Box 100, FI-70029, Kuopio, Finland, sami.myllymaa@uef.fi.
authors.forename: Sami
authors.initials: S
authors.lastname: Myllymaa
authors.forename: Katja
authors.initials: K
authors.lastname: Myllymaa
authors.forename: Salla
authors.initials: S
authors.lastname: Kupari
authors.forename: Antti
authors.initials: A
authors.lastname: Kulkas
authors.forename: Timo
authors.initials: T
authors.lastname: Leppänen
authors.forename: Pekka
authors.initials: P
authors.lastname: Tiihonen
authors.forename: Esa
authors.initials: E
authors.lastname: Mervaala
authors.forename: Juha
authors.initials: J
authors.lastname: Seppä
authors.forename: Henri
authors.initials: H
authors.lastname: Tuomilehto
authors.forename: Juha
authors.initials: J
authors.lastname: Töyräs
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D018670:Monitoring, Ambulatory; D010100:Oxygen / Q000097:blood*; D017286:Polysomnography; D012189:Retrospective Studies; D020181:Sleep Apnea, Obstructive / Q000097:blood* / Q000145:classification* / Q000628:therapy; D013223:Statistics as Topic
chemical_list: D010100:Oxygen