Cardiogenic oscillations on the airflow signal during continuous positive airway pressure as a marker of central apnea

Therapeutic decisions in patients with sleep apnea (eg, adjustment of conti nuous positive airway pressure [CPAP]) depend on differentiating central fr om obstructive apnea. Obstructive apnea is defined by cessation of airflow in the presence of continued respiratory effort, which is conventionally in ferred from chest wall movement or intrathoracic pressure swings. Cardiogen ic oscillations in the airflow have been observed during some central apnea s, but there is controversy over whether they cor relate with airway patenc y. The present study investigates whether these oscillations are markers of the absence of respiratory effort (central apnea) without regard to airway patency. Methods: We examined 648 apneas in 52 patients undergoing nocturnal polysom nograms and CPAP titrations, Airflow was measured using the output of the C PAP generator, and apneas were identified from reduction of airflow to < 10 % for > 10 s, We used only the presence or complete absence of thoracoabdom inal motion to classify apneas: obstructive apnea when motion was present ( 297 apneas); and central apnea if motion was totally absent (351 apneas). C entral apneas most often occurred at sleep onset or followed arousal with a big breath. Using only the flow signal, all apneas were examined for the p resence of cardiogenic oscillation by an observer blinded to other signals and apnea types. Results: No obstructive apnea show ed definite cardiogenic oscillations. In four cases, there was a suggestion of oscillation that was not regular eno ugh to be called cardiac. Sixty percent of central apneas showed clear, reg ular oscillations at cardiac frequency. Cardiogenic oscillations also were seen intermittently during quiet exhalation in apnea-fi ee periods. Conclusion: The presence of cardiogenic oscillations on the CPAP flow signa l is a specific indicator of central apnea and may have a role in self-titr ating CPAP algorithms, We speculate that transmission of these cardiac-indu ced oscillations may relate to the relaxation of thoracic muscles during ce ntral apnea and is impeded by high muscle tone during obstructive apnea.