title: Obesity hypoventilation syndrome in Japan and independent determinants of arterial carbon dioxide levels.
abstract: OBJECTIVE
  Obesity hypoventilation syndrome (OHS) prevalence was previously estimated at 9% in patients with obstructive sleep apnoea (OSA) in Japan. However, the definition of OSA in that study was based on an apnoea-hypopnoea index (AHI) of ≥ 20/h rather than ≥ 5/h. Therefore, the prevalence of OHS in OSA was not measured in the same way as for Western countries. Our study objectives were to investigate the characteristics of Japanese patients with OHS.
  
  
  METHODS
  Nine hundred eighty-one consecutive patients investigated for suspected OSA were enrolled. At least 90% of them were from urban areas, including 162 with obese OSA (body mass index (BMI) ≥ 30 kg/m(2) and AHI ≥ 5/h).
  
  
  RESULTS
  The prevalence of OHS (BMI 36.7 ± 4.9 kg/m(2) ) in OSA and that in obese OSA were 2.3% and 12.3%, respectively. Multiple regression analysis revealed that independent of age and BMI, arterial oxygen pressure (contribution rate (R(2) ) = 7.7%), 4% oxygen desaturation index (R(2)  = 8.9%), carbon monoxide diffusing capacity/alveolar volume (R(2)  = 8.3%), haemoglobin concentration (R(2)  = 4.9%) and waist circumference (R(2)  = 4.9%) were independently associated with arterial carbon dioxide pressure. After 12.3 ± 4.6 months of CPAP treatment, more than 60% of OHS patients no longer had hypercapnia.
  
  
  CONCLUSIONS
  The prevalence of OHS in OSA in Japan was 2.3%. The mean BMI of patients with OHS in Japan was lower than that in Western countries (36.7 kg/m(2) vs 44.0 kg/m(2) ).
authors.affiliation: Department of Respiratory Medicine, Graduate School of Medicine, Kyoto University, Kyoto, Japan.
authors.forename: Yuka
authors.initials: Y
authors.lastname: Harada
authors.forename: Yuichi
authors.initials: Y
authors.lastname: Chihara
authors.forename: Masanori
authors.initials: M
authors.lastname: Azuma
authors.forename: Kimihiko
authors.initials: K
authors.lastname: Murase
authors.forename: Yoshiro
authors.initials: Y
authors.lastname: Toyama
authors.forename: Chikara
authors.initials: C
authors.lastname: Yoshimura
authors.forename: Toru
authors.initials: T
authors.lastname: Oga
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Nakamura
authors.forename: Michiaki
authors.initials: M
authors.lastname: Mishima
authors.forename: Kazuo
authors.initials: K
authors.lastname: Chin
mesh_terms: D000328:Adult; D000368:Aged; D001784:Blood Gas Analysis; D001785:Blood Gas Monitoring, Transcutaneous / Q000379:methods; D015992:Body Mass Index; D002245:Carbon Dioxide / Q000097:blood*; D045422:Continuous Positive Airway Pressure / Q000379:methods; D005260:Female; D006801:Humans; D006935:Hypercapnia / Q000503:physiopathology; D007564:Japan / Q000453:epidemiology; D008297:Male; D008875:Middle Aged; D009765:Obesity / Q000150:complications / Q000175:diagnosis / Q000453:epidemiology; D010845:Obesity Hypoventilation Syndrome / Q000097:blood / Q000175:diagnosis / Q000453:epidemiology / Q000503:physiopathology; D017286:Polysomnography / Q000379:methods; D015995:Prevalence
chemical_list: D002245:Carbon Dioxide
keywords: diffusion capacity; hypercapnia; hypoventilation; obesity; sleep apnoea