Airway Obstruction, Obesity and CO₂ Ventilatory Responsiveness in the Sleep Apnea Syndrome

Abstract

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 uvulopalato-pharyngoplasty. Nine of the SAS patients had airway obstruction (AO-SAS), defined as FEV_1.0 ≤ 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 FEV_1.0 was ≤ 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.