Immediate consequences of respiratory events in sleep disordered breathing

Background: In obstructive sleep apnea/hypopnea syndrome, immediate physiological consequences of events have a dual role: censoring artifacts and gauging physiological significance. Newer airflow monitors may have changed the relative importance of these functions. The purpose of this study was to determine the frequency and hierarchy of occurrence of oxygen desaturation, EEG arousal and heart rate changes as immediate consequences of respiratory events. Methods: Thirty-nine sleep apnea patients underwent polysomnography with airflow detection by nasal cannula. Eighty events/subject were randomly selected and evaluated for 4% oxygen desaturation, EEG arousal and heart rate increase. Results: Of apneas, 78% caused desaturation, 6 3% arousal, and 73% heart rate increase. Of hypopneas, 54% caused desaturation, 47% arousal, and 55% heart rate increase. Of events with mildest amplitude reduction 25% caused desaturation, 42% arousal, and 42% heart rate increase. Consequences overlapped but did not occur hierarchically: each occurred alone and in all combinations. Conclusion: No single consequence occurred after every event; thus none can be used to corroborate airflow reduction as non-artifactual without missing events corroborated by other consequences. As different consequences validate non-hierarchical sets of respiratory events, we propose there is need to capture all changes in breathing in obstructive sleep apnea/hypopnea syndrome before examining their role in clinical outcome.