title: Determinants of chronic hypercapnia in Japanese men with obstructive sleep apnea syndrome.
abstract: OBJECTIVE
  To identify the determinants of chronic hypercapnia (ie, PaCO(2), > or = 45 mm Hg) in men with obstructive sleep apnea syndrome (OSAS) without airflow obstruction.
  
  
  METHODS
  An analysis was conducted of 143 male patients with OSAS, which had been diagnosed by polysomnography (PSG), who had been referred to a university hospital. Patients were classified as hypercapnic (ie, PaCO(2), > or = 45 mm Hg) and normocapnic (ie, PaCO(2), < 45 mm Hg), and obese (ie, body mass index [BMI], > or = 30 kg/m(2)) or nonobese (ie, BMI, < 30 kg/m(2)). Patients with airflow obstruction (ie, FEV(1)/FVC ratio, < 70%) were excluded from the study. Baseline clinical characteristics, pulmonary function, PSG data, and blood gas data were compared between hypercapnic and normocapnic patients. Correlations between PaCO(2) and several anthropometric, respiratory, and polysomnographic variables were determined by stepwise multiple regression analysis.
  
  
  RESULTS
  Fifty-five patients (38%) were hypercapnic. Hypercapnic patients were younger and heavier, and had more abnormalities on pulmonary and PSG testing. Stepwise multiple regression analysis revealed that the PaCO(2) level was influenced significantly by the mean level of arterial oxygen saturation (SaO(2)) during sleep and by the percent of vital capacity (%VC) (R(2) = 0.430; p < 0.0001), indicating that 43% of the total variance in the PaCO(2) could be explained by the mean SaO(2) and %VC in hypercapnic patients. In contrast, only 13% of the total variance in the PaCO(2) was accounted for by the mean SaO(2) and BMI in normocapnic patients (R(2) = 0.134; p = 0.0034). The mean SaO(2), %VC, and PaO(2) were selected as independent variables for predicting the PaCO(2) in obese patients. These variables explained 41% of the total variance in the PaCO(2) (R(2) = 0.407; p < 0.0001), whereas the mean SaO(2) only accounted for 13% of the total variance in PaCO(2) levels in nonobese patients (R(2) = 0.134; p = 0.0064).
  
  
  CONCLUSIONS
  Nocturnal desaturation and restrictive pulmonary impairment play major roles in determining the PaCO(2) in hypercapnic and obese OSAS patients without airflow obstruction.
authors.affiliation: First Department of Internal Medicine, Nihon University School of Medicine, Tokyo, Japan.
authors.forename: Tsuneto
authors.initials: T
authors.lastname: Akashiba
authors.forename: Seiji
authors.initials: S
authors.lastname: Kawahara
authors.forename: Naoko
authors.initials: N
authors.lastname: Kosaka
authors.forename: Daisuke
authors.initials: D
authors.lastname: Ito
authors.forename: Osamu
authors.initials: O
authors.lastname: Saito
authors.forename: Tohru
authors.initials: T
authors.lastname: Majima
authors.forename: Takashi
authors.initials: T
authors.lastname: Horie
mesh_terms: D000328:Adult; D000368:Aged; D015992:Body Mass Index; D002245:Carbon Dioxide / Q000032:analysis; D002908:Chronic Disease; D006801:Humans; D006935:Hypercapnia / Q000209:etiology*; D008297:Male; D008875:Middle Aged; D009765:Obesity / Q000150:complications; D010100:Oxygen / Q000032:analysis; D010313:Partial Pressure; D012891:Sleep Apnea Syndromes / Q000150:complications* / Q000503:physiopathology
chemical_list: D002245:Carbon Dioxide; D010100:Oxygen