Apnea may be central, obstructive, or mixed based on polysomnographic findings. This classification contributes to determine the possible sites of nervous system involvement (Figure 18.1). The classification is based on two factors: (1) nasal and oral airflow, and (2) chest and abdominal movements.

Figure 18.1— Sites of possible lesions producing central apnea. A: chemoreceptor; B: respiratory groups; C: cervico-medullary junction; D: anterior horn cells of the phrenic nerve; E: phrenic nerve; F: myoneural junction; G: diaphragm.