RELEASE OF UPPER AIRWAY MUSCLE INHIBITION DURING AIRWAY OCCLUSION

Abstract

Control of upper airway(UA) muscles appears essential for maintenance of pharyngeal patency. Animal studies indicate that volume-related vagal inhibition during inspiration modulates UA muscles more than the diaphragm(DIA). To determine if preferential inhibition of UA muscles occurs in neonates during normal inspiration, we studied 9 infants (GA 30±3 wks, age 15±8 days, Wt 1.1±0.2 kg) by performing 9 (range 5-16) end expiratory nasal occlusions during sleep. We recorded UA EMG (via surface submental electrodes), surface DIA EMG, ventilation, esophageal and mask pressures.Phasic inspiratory EMG occurred in 52±36% of unoccluded breaths and increased to 78±27%(p<.02) in the first occluded effort. Peak UA EMG during unoccluded breathing was 58±28% of that during the first occluded effort (p<.001). This increase in UA EMG activity during occlusion was accompanied by an increase in time to peak UA EMG from 250±91 to 612±63 MS (p<.001), while the rate of rise did not change. In contrast, peak activity, time to peak, and rate of rise of DIA EMG were unchanged during the first occluded effort. Esophageal pressures were consistently transmitted to the nasal mask during occlusion, indicating UA patency. These data indicate that feedback associated with lung inflation inhibits UA EMG more than DIA EMG during normal breathing. Release of this inhibition during airway obstruction, with the concomitant increase in UA muscle activity, may be a major mechanism for maintenance of pharyngeal patency in preterm infants. Supported by NIH HL31173 and HL25830