Negative upper airway pressure is thought to play a key role in the pathophysiology of obstructive sleep apnea. Because nasal resistance contributes to the increase of the transpharyngeal pressure gradient, we evaluated the effects of nasal surgery on sleep-related breathing abnormalities in 20 adults with obstructive sleep apnea. Polysomnographic studies were done before (baseline), and 2 to 3 mo after surgery (septoplasty, turbinectomy, and/or polypectomy). Nasal resistances were measured at these visits in 14 patients. Cephalometric measurements were obtained before surgery. Cephalometric abnormalities consisted in an increase in the distance from the mandibular plane to the hyoid bone (MP-H), a decrease in the space between the base of the tongue and the posterior soft tissues (PAS), a retroposition of the mandibule, and an increase in the length of the soft palate. Body weight did not change between the two studies. Nasal resistance decreased significantly after nasal surgery. The composition of the total sleep time spent in the rapid eye movement stage increased from 11.5 +/- 1.3% (mean +/- SEM) to 14 +/- 1.2% after surgery. For the group as the whole, there was no difference between baseline and postsurgical values in the frequency of respiratory disturbances (39.8 +/- 6.1, 36.8 +/- 5.9 n/h), the total apnea time (17.8 +/- 4.2, 15.4 +/- 2.8), the distribution of the apnea time within the different apnea types (obstructive and nonobstructive), and the severity of the nocturnal desaturations. Interestingly, apnea and apnea plus hypopnea indices returned to normal values (< 5 and 10, respectively) in four subjects with normal posterior soft tissues and mandibular plane to the hyoid bone distances.(ABSTRACT TRUNCATED AT 250 WORDS)