title: Adjustment of apnea-hypopnea index with severity of obstruction events enhances detection of sleep apnea patients with the highest risk of severe health consequences.
abstract: BACKGROUND
  Presently, the severity of obstructive sleep apnea (OSA) is estimated based on the apnea-hypopnea index (AHI). Unfortunately, AHI does not provide information on the severity of individual obstruction events. Previously, the severity of individual obstruction events has been suggested to be related to the outcome of the disease. In this study, we incorporate this information into AHI and test whether this novel approach would aid in discriminating patients with the highest risk. We hypothesize that the introduced adjusted AHI parameter provides a valuable supplement to AHI in the diagnosis of the severity of OSA.
  
  
  METHODS
  This hypothesis was tested by means of retrospective follow-up (mean ± sd follow-up time 198.2 ± 24.7 months) of 1,068 men originally referred to night polygraphy due to suspected OSA. After exclusion of the 264 patients using CPAP, the remaining 804 patients were divided into normal (AHI < 5) and OSA (AHI ≥ 5) categories based on conventional AHI and adjusted AHI. For a more detailed analysis, the patients were divided into normal, mild, moderate, and severe OSA categories based on conventional AHI and adjusted AHI. Subsequently, the mortality and cardiovascular morbidity in these groups were determined.
  
  
  RESULTS
  Use of the severity of individual obstruction events for adjustment of AHI led to a significant rearrangement of patients between severity categories. Due to this rearrangement, the number of deceased patients diagnosed to have OSA was increased when adjusted AHI was used as the diagnostic index. Importantly, risk ratios of all-cause mortality and cardiovascular morbidity were higher in moderate and severe OSA groups formed based on the adjusted AHI parameter than in those formed based on conventional AHI.
  
  
  CONCLUSIONS
  The adjusted AHI parameter was found to give valuable supplementary information to AHI and to potentially improve the recognition of OSA patients with the highest risk of mortality or cardiovascular morbidity.
authors.affiliation: Department of Clinical Neurophysiology, Kuopio University Hospital, P.O. Box 100, KYS, Finland, Anu.Muraja-Murro@kuh.fi.
authors.forename: A
authors.initials: A
authors.lastname: Muraja-Murro
authors.forename: A
authors.initials: A
authors.lastname: Kulkas
authors.forename: M
authors.initials: M
authors.lastname: Hiltunen
authors.forename: S
authors.initials: S
authors.lastname: Kupari
authors.forename: T
authors.initials: T
authors.lastname: Hukkanen
authors.forename: P
authors.initials: P
authors.lastname: Tiihonen
authors.forename: E
authors.initials: E
authors.lastname: Mervaala
authors.forename: J
authors.initials: J
authors.lastname: Töyräs
mesh_terms: D000328:Adult; D000368:Aged; D002318:Cardiovascular Diseases / Q000175:diagnosis / Q000209:etiology / Q000401:mortality; D002423:Cause of Death; D005387:Finland; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D008875:Middle Aged; D017286:Polysomnography; D012189:Retrospective Studies; D012306:Risk; D012720:Severity of Illness Index; D020181:Sleep Apnea, Obstructive / Q000145:classification* / Q000150:complications* / Q000175:diagnosis / Q000401:mortality; D015996:Survival Rate