[Obesity hypoventilation syndrome and obstructive sleep apnea syndrome: is there an association?].

Background: Severe obesity sometimes leads to a chronic alveolar hypoventilation: obesity hypoventilation syndrome (OHS), (Pao2<70mmHG, Paco2>45mmHG and body mass index (BMI)>30Kg/m2). The association with an OSAS is frequent.
Aim: To assess predicting factors that lead to hypoventilation in a population of obese patients with SAS and to deduct the type of association between OHS and SAS.
Methods: We have study during 4 years, at pneumology service of Charles Nicolle hospital, 62 obese patients (BMI>30Kg /m2), 41men and 21 women and presenting an OSAS. We excluded those carriers of a bronchial obstruction (VEMS/CV <60%) and we have compared anthropométriques, functional, gazométriques and polysomographiques details of the groupe1 (G1): OHS=9 and of the groupe2 (G2): obesity without hypoventilation (n=53).
Results: We didn't identified any significant difference between the two groups concerning (age, sex, the frequency of smokers, the frequency of the nasopharynx region abnormalities, apnea-hypopnea index (AHI), the SAS severity and the respiratory functional exploration). The obesity is significant more important in the G1, it is sever (BMI>40) in 77.8% of patients of the G1 with significant difference with the G2 (P=0.004). We noted that there is a positive interrelationship between BMI and Paco2. We identified severe gazométrique perturbation in G1 (Pao2 medium = 61± 9 mmHg,Paco2 medium=50 ± 7 mmHg), in the G2 we noted a moderate hypoxemia. Patients of the group1 make of the minimal desaturation of 63 ± 17% and a Sao2 average of 81 ± 20% what is meaningfully more important than in the G2.
Conclusion: The alveolar hypoventilation in SAS seems to be in correlation with the degree of obesity. The hypercapnie in the OHS is in relation neither with the SAOS nor with its severity. The OHSSAS association is usual but not synonym; the OHS is an autonomous disease.