Dynamics of respiratory drive and pressure during NREM sleep in patients with occlusive apneas

To study the dynamics of respiratory drive and pressure in patients with occlusive apneas, diaphragmatic electromyogram (EMGdi), esophageal pressure (Pes), and genioglossal electromyogram (EMGge) were monitored during nocturnal sleep in five patients. Both EMGs were analyzed as peak moving time average, and Pes was quantitated as the peak inspiratory change from base line. During the ventilatory phase both EMGs decreased proportionally. The decrease in Pes was less than the decrease observed in EMGdi, and Pes generated for a given EMGdi increased during the preapneic phase in spite of the proportional decrease in EMGdi and EMGge during this period. We conclude that negative inspiratory pressures which lead to the passive collapse of oropharyngeal walls are dependent on both respiratory and upper airway muscle activity and that occlusive apneas of non-rapid-eye-movement (NREM) sleep do occur in spite of proportional changes observed in the activity of both muscle groups. The preapneic increase in negative inspiratory pressures generated for a given respiratory muscle activity is most likely due to the decrease in upper airway muscle activity that is associated with an increase in oropharyngeal resistance.