Airway obstruction, obesity and CO2 ventilatory responsiveness in the sleep apnea syndrome.

In 32 patients with sleep apnea syndrome (SAS), pulmonary function, blood gases and the ventilatory response to CO2 (CO2 VR) were studied before and 6 months after uvulopalatopharyngoplasty. Nine of the SAS patients had airway obstruction (AO-SAS), defined as FEV1.0 < or = 72% of the predicted value. They had a significantly higher PaCO2, lower PaO2 and a lower CO2 VR than the remaining SAS patients. Preoperatively 4 SAS patients were hypercapnic (PaCO2 > 5.8 kPa) and compared with the normocapnic ones they were more obese; in 3 of them FEV1.0 was < or = 72%. The hypercapnic SAS patients had a significantly lower CO2 VR. The CO2 VR was significantly correlated to AO and the degree of oxygen desaturation during sleep, but not to the number of episodes of apnea and hypopnea nor their length. The VR to CO2 did not predict the postoperative outcome. Postoperatively 2 hypercapnic obese AO-SAS patients showed a large decrease in episodes of apnea and hypopnea and an increase in CO2 VR, and became normocapnic. Other patients showed no consistent changes in CO2 VR postoperatively.