Determinants of chronic hypercapnia in Japanese men with obstructive sleep apnea syndrome.
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.
Akashiba
Tsuneto
T
First Department of Internal Medicine, Nihon University School of Medicine, Tokyo, Japan.
Kawahara
Seiji
S
Kosaka
Naoko
N
Ito
Daisuke
D
Saito
Osamu
O
Majima
Tohru
T
Horie
Takashi
T
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
D002245:Carbon Dioxide; D010100:Oxygen