Changes in end-expiratory lung volume during sleep in patients with occlusive apnea

Eight patients with occlusive sleep apnea were monitored during non-rapid-eye-movement (NREM) sleep to study the factors that contribute to negative inspiratory pressure generation and thus upper airway occlusion. End-expiratory lung volume assessed by respiratory inductive plethysmography [sum of end-expiratory levels (SUM EEL)] increased early and decreased late during the ventilatory phases (P less than 0.0001, one-way analysis of variance). Inspiratory change in esophageal pressure (Pes) and peak inspiratory diaphragmatic and genioglossal electromyograms (EMGdi and EMGge) decreased while the inspiratory pressure generated for a given diaphragmatic activity (Pes/EMGdi) increased during the preapneic phase (P less than 0.0001, for all). Multiple regression analysis with Pes/EMGdi as the dependent variable (R2 = 0.90) indicated that both the changes in SUM EEL and EMGge significantly contributed to the model (P less than 0.008 and 0.004, respectively). These results indicate that end-expiratory lung volume fluctuates during NREM sleep in patients with occlusive apnea and suggest that these changes along with the changes in upper airway muscle activity contribute to the generation of negative inspiratory pressure, leading to the passive collapse of the upper airways.