1696 EFFECTS OF UPPER AIRWAY (UA) INTRALUMINAL PRESSURE ON RESPIRATORY FREQUENCY

Abstract

Reduced respiratory frequency (f) is seen during obstructive and mixed apnea. Since intrathoracic pressure changes in obstructive and mixed apnea are conducted to the larynx and pharynx, we wondered if UA pressure changes could contribute to the reduced f, in addition to lung and chemoreceptor reflexes. Therefore, we studied the effects of UA pressure changes on f by raising or lowering the pressure in the isolated UA (nose, pharynx and larynx) during tracheostomy breathing and by adding respiratory loads (airway occlusion) after eliminating lung stretch reflexes by cervical vagotomy. Comparison of the first occluded with the preceding breath eliminated chemoreceptor influences. The integrated diaphragmatic EMG was used to determine f. The effect of a sustained pressure change in the isolated UA was tested in 15 anesthetized (Pentothol) rabbits. A rapid decrease in f during negative pressure change (up to 35%) and an increase in f during positive pressure change (up to 20%) were seen. The percentage change in f correlated with the magnitude of pressure change (2-10cm H2O). The nasal or tracheostomy airway was occluded briefly (at FRC) in 6 vagotomized animals. During nasal occlusion inspiratory and respiratory cycle duration was prolonged (10-20%) whereas no change was seen during tracheostomy occlusion. We conclude that response to UA pressure changes may contribute to the reduced respiratory frequency seen during mixed and obstructive apnea. (Funding: NIH grant#HD10993)