title: Effect of oxygen desaturation threshold on determination of OSA severity during weight loss.
abstract: OBJECTIVE
  Weight loss leads to improvement of obstructive sleep apnea (OSA), based on frequency of respiratory events (apnea-hypopnea index, AHI). However, AHI does not incorporate the severity of individual obstruction events. The American Academy of Sleep Medicine suggests two alternative oxygen desaturation thresholds (ODT) for scoring of hypopneas. We hypothesize that lowering the ODT level increases the determined impact of weight loss on OSA severity. We investigate this during weight change with AHI and adjusted AHI. Adjusted AHI is a novel parameter incorporating both severity and number of the events.
  
  
  METHODS
  Ambulatory polygraphic data of 54 OSA patients (F 15/M 39, 51.7 ± 8.4 years), divided into weight loss (>5 %, n = 20), control (weight change 0-5 %, n = 26), and weight gain (>5 %, n = 8) groups, were evaluated at baseline and after 5-year follow-up. Effect of ODT (ODT2%-ODT6%) on AHI and adjusted AHI was investigated.
  
  
  RESULTS
  The greatest changes in AHI (decrease in weight loss group and increase in weight gain group) were observed with ODT2%. Changes in AHI diminished with increasing ODT. In weight loss group, adjusted AHI showed a similar but non-significant trend. In contrast, the higher ODT was used in weight gain group, the greater increase in adjusted AHI resulted. Using adjusted AHI instead of AHI, led to a smaller number of patients (20 vs. 55 %, ODT3%) whose OSA severity category improved along weight loss.
  
  
  CONCLUSIONS
  Weight loss significantly reduced AHI. This reduction was highly dependent on selected ODT. The change in adjusted AHI did not occur in the same extent. This was expected as the more severe events which tend to remain during the weight loss have greater importance in adjusted AHI, while the event severity is neglected in AHI.
authors.affiliation: Department of Clinical Neurophysiology, Kuopio University Hospital, PO Box 100, 70029, Kuopio, Finland.
authors.forename: Katja
authors.initials: K
authors.lastname: Myllymaa
authors.affiliation: Department of Clinical Neurophysiology, Kuopio University Hospital, PO Box 100, 70029, Kuopio, Finland. sami.myllymaa@uef.fi.|Department of Applied Physics, University of Eastern Finland, Kuopio, Finland. sami.myllymaa@uef.fi.|Institute of Dentistry, University of Eastern Finland, Kuopio, Finland. sami.myllymaa@uef.fi.
authors.forename: Sami
authors.initials: S
authors.lastname: Myllymaa
authors.affiliation: Department of Clinical Neurophysiology, Kuopio University Hospital, PO Box 100, 70029, Kuopio, Finland.|Department of Applied Physics, University of Eastern Finland, Kuopio, Finland.
authors.forename: Timo
authors.initials: T
authors.lastname: Leppänen
authors.affiliation: Department of Clinical Neurophysiology, Seinäjoki Central Hospital, Seinäjoki, Finland.
authors.forename: Antti
authors.initials: A
authors.lastname: Kulkas
authors.affiliation: Department of Clinical Neurophysiology, Kuopio University Hospital, PO Box 100, 70029, Kuopio, Finland.|Institute of Clinical Medicine, University of Eastern Finland, Kuopio, Finland.
authors.forename: Salla
authors.initials: S
authors.lastname: Kupari
authors.affiliation: Department of Clinical Neurophysiology, Kuopio University Hospital, PO Box 100, 70029, Kuopio, Finland.
authors.forename: Pekka
authors.initials: P
authors.lastname: Tiihonen
authors.affiliation: Department of Clinical Neurophysiology, Kuopio University Hospital, PO Box 100, 70029, Kuopio, Finland.|Institute of Clinical Medicine, University of Eastern Finland, Kuopio, Finland.
authors.forename: Esa
authors.initials: E
authors.lastname: Mervaala
authors.affiliation: Institute of Clinical Medicine, University of Eastern Finland, Kuopio, Finland.|Department of Otorhinolaryngology, Kuopio University Hospital, Kuopio, Finland.
authors.forename: Juha
authors.initials: J
authors.lastname: Seppä
authors.affiliation: Oivauni Sleep Clinic, Kuopio, Finland.|Institute of Public Health and Clinical Nutrition, University of Eastern Finland, Kuopio, Finland.
authors.forename: Henri
authors.initials: H
authors.lastname: Tuomilehto
authors.affiliation: Department of Clinical Neurophysiology, Kuopio University Hospital, PO Box 100, 70029, Kuopio, Finland.|Department of Applied Physics, University of Eastern Finland, Kuopio, Finland.
authors.forename: Juha
authors.initials: J
authors.lastname: Töyräs
mesh_terms: D000328:Adult; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D018670:Monitoring, Ambulatory; D010100:Oxygen / Q000097:blood*; D017286:Polysomnography; D020181:Sleep Apnea, Obstructive / Q000175:diagnosis* / Q000503:physiopathology*; D015431:Weight Loss / Q000502:physiology*
chemical_list: D010100:Oxygen
keywords: Adjusted AHI; Apnea-hypopnea index (AHI); Hypopnea; Hypoxia; Obstructive sleep apnea (OSA); Oxygen desaturation; Weight loss