Figure 19.1.— Central apnea (cessation of airflow at the nose and mouth, and absence of thoracic and abdominal movements). Sleep stage: quiet sleep (tracé alternant and regular respiration), bradycardia, and desaturation.
Central apnea is due to failure of the diaphragm to generate negative intrathoracic pressure. Lesions at multiple levels in the ventilatory system can lead to central apnea (Figure 19.2 A-G).
Figure 19.2— 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.
The polysomnographic characteristics of obstructive apnea are absence of nasal and oral airflow in the presence of thoracic or abdominal movements (Figure 19.3).
Figure 19.3.— Obstructive apnea (cessation of nasal airflow despite thoracic and abdominal respiratory movements). EEG shows low-voltage irregular activity. The apnea is followed by tachycardia and desaturation.
Paradoxical chest/abdominal movement is a frequent polysomnographic finding during obstructive apnea. Normally the chest circumference increases during inspiration and decreases during expiration, and the abdominal circumference increases during inspiration and decreases during expiration. In obstructive apnea the chest circumference decreases during inspiration and increases during expiration. This situation is referred to as paradoxical breathing. Paradoxical breathing can occur without apnea (Figure 19.4).