The assessment of upper airway patency during apnea using cardiogenic oscillations in the airflow signal.

We investigated the relationship between airway patency and the occurrence of cardiogenic related oscillations in the airflow signal during 67 apneas occurring in non-rapid eye movement sleep in eight subjects. Spontaneously occurring apneas and apneas induced by mechanical ventilation were analyzed. Airway occlusion was determined by direct observation of the pharyngeal lumen using fiberoptic endoscopy. The presence or absence of cardiogenic oscillations was determined from an expanded airflow signal by an investigator blinded to the airway patency. Of the total 67 apneas, complete airway occlusion occurred during 51, and the airway remained patent throughout in 16. Cardiogenic oscillations were seen throughout 39 of the 51 occluded apneas and throughout 9 of the 16 apneas with the airway patent. There was no relationship between the occurrence of cardiogenic oscillations and airway patency. In addition, in a canine model where the upper airway was anatomically isolated, cardiogenic oscillations were evident during apneas in pressure signals recorded from the isolated upper airway and in airflow signals at the tracheal stoma. We conclude that cardiogenic oscillations cannot be used to predict airway patency during apnea.