Chest
Volume 121, Issue 2, February 2002, Pages 415-421
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Clinical Investigations
Sleep and Breathing
Determinants of Chronic Hypercapnia in Japanese Men With Obstructive Sleep Apnea Syndrome

https://doi.org/10.1378/chest.121.2.415Get rights and content

Study objective

To identify the determinants of chronic hypercapnia (ie, Paco2, ≥45 mm Hg) in men with obstructive sleep apnea syndrome (OSAS) without airflow obstruction.

Design

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, Paco2, ≥45 mm Hg) and normocapnic (ie, Paco2, < 45 mm Hg), and obese (ie, body mass index [BMI], ≥30 kg/m2) or nonobese (ie, BMI, < 30 kg/m2). Patients with airflow obstruction (ie, FEV1/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 Paco2 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 Paco2 level was influenced significantly by the mean level of arterial oxygen saturation (Sao2) during sleep and by the percent of vital capacity (%VC) (R2 = 0.430; p < 0.0001), indicating that 43% of the total variance in the Paco2 could be explained by the mean Sao2 and %VC in hypercapnic patients. In contrast, only 13% of the total variance in the Paco2 was accounted for by the mean Sao2 and BMI in normocapnic patients (R2 = 0.134; p = 0.0034). The mean Sao2, %VC, and Pao2 were selected as independent variables for predicting the Paco2 in obese patients. These variables explained 41% of the total variance in the Paco2 (R2 = 0.407; p < 0.0001), whereas the mean Sao2 only accounted for 13% of the total variance in Paco2 levels in nonobese patients (R2 = 0.134; p = 0.0064).

Conclusion

Nocturnal desaturation and restrictive pulmonary impairment play major roles in determining the Paco2 in hypercapnic and obese OSAS patients without airflow obstruction.

Section snippets

Materials and Methods

The study cohort consisted of 146 male patients who had received a diagnosis of OSAS based on the results of polysomnography (PSG). Patients with airway obstruction (ie, FEV1/FVC ratio, < 70%) were excluded from this study. All patients gave informed consent for participation. No patients had chronic lung disease or were receiving bronchodilator therapy.

A full night of PSG with continuous recordings of the EEG, electrooculogram, submental electromyogram, ECG, airflow at the nose and mouth (by

Results

The mean age was 48.3 ± 11.3 years, and the mean BMI was 29.6 ± 5.7 kg/m2. The results of pulmonary function tests were normal in all but six of the patients who had restrictive ventilatory abnormalities (ie, percent vital capacity [%VC], < 80%). No patients had evidence of obstructive airway disease (FEV1/FVC ratio, < 70%). The average daytime Pao2 and Paco2 levels were 80.7 ± 9.6 and 44.5 ± 5.3 mm Hg, respectively. The comparisons between hypercapnic and normocapnic patients on baseline

Discussion

We found a relatively high incidence of daytime hypercapnia in patients with severe OSAS (38%). In previous studies,23478910 the prevalence of hypercapnia in patients with OSAS varied from 14 to 57%. However, the number of patients in these previous studies was small. In the largest study, Leech et al7 examined 111 patients with OSAS and found that 41 of 111 patients (36%) had chronic hypercapnia. Although alveolar hypoventilation, hypercapnia, and hypoxemia occur in some patients with chronic

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