title: Positional OSA part 2: retrospective cohort analysis with a new classification system (APOC).
abstract: BACKGROUND
  In Part 1 of this two-part article, the Amsterdam Positional Obstructive Sleep Apnoea Classification (APOC) was recently introduced, a classification system aimed at facilitating the identification of suitable candidates for positional therapy (PT): patients who will benefit from a clinically significant improvement of their obstructive sleep apnoea (OSA) with PT. APOC was developed with new generation PT devices in mind rather than conventional PT (tennis ball technique). New generation PT can be defined as a well-tolerated device which prevents a patient from adopting the worst sleeping position (WSP) without negatively influencing sleep efficiency, as objectified by a full night polysomnography (PSG). PT is rapidly gaining momentum in the scope of OSA treatment. The objective of this manuscript is to measure the prevalence of position-dependent obstructive sleep apnoea (POSA) according to the APOC, in a consecutive series of patients referred for PSG as well as an investigation of associations between POSA and certain patient characteristics.
  
  
  METHODS
  We performed a retrospective, single-centre cohort study including a consecutive series of patients who underwent a PSG during the period of April 2010 until October 2010.
  
  
  RESULTS
  Within this OSA-cohort (n = 253), a prevalence of POSA of 69 % when applying APOC is measured, compared to 64 % when applying Cartwright's classification. An inverse relation between POSA and BMI was observed, likewise between POSA and apnoea hypopnoea index (AHI).
  
  
  CONCLUSIONS
  We are of opinion that APOC is a suitable tool to identify patients who will or will not benefit from PT, thus resulting in more cost-efficient treatment.
authors.affiliation: Department of Otolaryngology/Head Neck Surgery, Sint Lucas Andreas Ziekenhuis, Jan Tooropstraat 164, 1061 AE, Amsterdam, The Netherlands. m.j.l.ravesloot@amc.uva.nl.
authors.forename: M J L
authors.initials: MJ
authors.lastname: Ravesloot
authors.affiliation: Department of Otolaryngology/Head Neck Surgery, Sint Lucas Andreas Ziekenhuis, Jan Tooropstraat 164, 1061 AE, Amsterdam, The Netherlands. mka.mhfrank@gmail.com.|Department of Oral and Maxillofacial Surgery, Academic Medical Centre, University of Amsterdam, Amsterdam, The Netherlands. mka.mhfrank@gmail.com.
authors.forename: M H
authors.initials: MH
authors.lastname: Frank
authors.affiliation: Department of Otolaryngology/Head Neck Surgery, Sint Lucas Andreas Ziekenhuis, Jan Tooropstraat 164, 1061 AE, Amsterdam, The Netherlands.
authors.forename: J P
authors.initials: JP
authors.lastname: van Maanen
authors.affiliation: Department of Epidemiology Public and Occupational Health, EMGO Institute for Health and Care Research, VU Medical Center, Amsterdam, The Netherlands.
authors.forename: E A
authors.initials: EA
authors.lastname: Verhagen
authors.affiliation: Department of Oral and Maxillofacial Surgery, Academic Medical Centre, University of Amsterdam, Amsterdam, The Netherlands.
authors.forename: J
authors.initials: J
authors.lastname: de Lange
authors.affiliation: Department of Otolaryngology/Head Neck Surgery, Sint Lucas Andreas Ziekenhuis, Jan Tooropstraat 164, 1061 AE, Amsterdam, The Netherlands.
authors.forename: N
authors.initials: N
authors.lastname: de Vries
mesh_terms: D015331:Cohort Studies; D003430:Cross-Sectional Studies; D004867:Equipment Design; D006801:Humans; D056888:Patient Positioning / Q000295:instrumentation; D018579:Patient Selection; D017286:Polysomnography; D011187:Posture; D012189:Retrospective Studies; D020181:Sleep Apnea, Obstructive / Q000145:classification* / Q000175:diagnosis / Q000453:epidemiology / Q000628:therapy*
keywords: Obstructive sleeping position; Positional therapy; Sleep apnoea