Patients with obstructive sleep apnea (OSA) experience severe sleep disruption and consequent daytime sleepiness. Current arousal scoring criteria show that some obstructive apneic events do not end in a recognizable cortical electroencephalographic (EEG) arousal. It is not known whether events that end in an obvious EEG arousal differ from those that do not, in terms of EEG frequency changes during the apneic event, the respiratory effort developed prior to apnea termination, the degree of the postapneic increase in blood pressure, or changes in CO2 tensions. We studied 15 patients with OSA in early Stage 2 sleep and analyzed obstructive apneic events with and without typical EEG arousals, defining an arousal as a frequency shift to waking alpha rhythm of 1 s or longer. EEG signals were digitized and analyzed by fast Fourier transform during and immediately after each apnea. The median EEG frequency and mean pleural pressure of the first and second halves of the apneic episode were compared with that of the first breath. Peak pleural pressure was measured just before the end of the apneic episode. Systolic and diastolic blood pressures and CO2 tensions were measured at the onset and termination of apnea. For each patient, 10 events that ended in EEG arousal were compared with 10 events that did not. Mean apnea duration did not differ for the two groups of events. Median EEG frequency and pleural pressure increased significantly from 8.14 to 9.25 Hz and 15.4 to 22.1 cm H2O, respectively, as the apnea progressed, but there was no difference between the groups nor any difference in the peak pleural pressure.(ABSTRACT TRUNCATED AT 250 WORDS)