Therapeutic decisions in patients with sleep apnea
(eg, adjustment of continuous positive airway pressure[
CPAP]) depend on differentiating central from obstructive apnea.
Obstructive apnea is defined by cessation of airflow in the presence of
continued respiratory effort, which is conventionally inferred from
chest wall movement or intrathoracic pressure swings. Cardiogenic
oscillations in the airflow have been observed during some central
apneas, but there is controversy over whether they correlate with
airway patency. The present study investigates whether these
oscillations are markers of the absence of respiratory effort (central
apnea) without regard to airway patency.
examined 648 apneas in 52 patients undergoing nocturnal polysomnograms
and CPAP titrations. Airflow was measured using the output of the CPAP
generator, and apneas were identified from reduction of airflow to< 10% for > 10 s. We used only the presence or complete absence of
thoracoabdominal motion to classify apneas: obstructive apnea when
motion was present (297 apneas); and central apnea if motion was
totally absent (351 apneas). Central 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 presence of cardiogenic
oscillation by an observer blinded to other signals and apnea
Results: No obstructive apnea showed definite
cardiogenic oscillations. In four cases, there was a suggestion of
oscillation that was not regular enough to be called cardiac. Sixty
percent of central apneas showed clear, regular oscillations at cardiac
frequency. Cardiogenic oscillations also were seen intermittently
during quiet exhalation in apnea-free periods.
Conclusion: The presence of cardiogenic oscillations on the
CPAP flow signal is a specific indicator of central apnea and may have
a role in self-titrating CPAP algorithms. We speculate that
transmission of these cardiac-induced oscillations may relate to the
relaxation of thoracic muscles during central apnea and is impeded by
high muscle tone during obstructive apnea.