Correlated Factors Of Chronic Hypercapnia In Patients With Obstructive Sleep Apnea-hypopnea Syndrome

Objective: To identify the correlated factors of chronic hypercapnia in patients with obstructive sleep apnea-hypopnea syndrome.Methods: The study cohort consisted 56 patients with OSAHS, which had been diagnosed by polysomnography (PSG). They were taken arterial blood gas analysis and pulmonary function tests. Patients were excluded if their FEV₁/FVC<70%. According to P_ACO₂ they were divided into two groups, hypercpanic (P^aCO₂≥45mmHg) and normocapnic (P_aCO₂ < 45mmHg). And according to body mass index (BMI), they were divided as obese (BMI≥ 30kg/m²) and nonobese (BMK30kg/m²). Their age, BMI, PSG data, pulmonary function data and blood gas data were recorded. And these recorded data were compared between hypercapnic and normocapnic, obese and nonobese patients respectively. Correlations between P_aCO₂ and these data's variables were determined by linear regression analysis. If the variable was correlated, it was included in the stepwise multiple regression analysis to determine its role to P_aCO₂ level.Results: Twenty-one patients (37%) were hypercapnic. Compared with normocapnic patients, hypercapnic patients were more obese, had more serioussleep breathing disturbance, restrictive ventilatory impairment and worse sleep quality. Even their daytime PaO2 were lower. Multiple regression analysis revealed that the percent of vital capacity (%VC) and the mean level of pulse oxygen saturation (SPO2) during sleep were two major variables that influenced the PaCO2 level significantly. The model including the two variables explained 74% of the total PaCO2 variance in hypercapnic patients (R2=0.738, p<0.001). In contrast, there were no variables in this study correlated with the PaCO2 level in normocapnic group. In obese group, %VC and mean SPO2 were also two major variables in determining PaCO2 level. The model accounted for 79% of total variance (R2=0.792, p< 0.001). Only the mean SPO2 was the major variable influenced the PaCO2 level in nonobese group. The model explained 55% of the total variance (R2=0.545, p<0.001).Conclusion: Restrictive ventilatory impairment and nocturnal oxygen desaturation play major roles in the development of chronic hypercapnia in OSAHS patients.