Laryngeal muscle response to phasic and tonic upper airway pressure and flow

The hypothesis that respiratory modulation due to upper airway (UA) pressur e and flow is dependent on stimulus modality and respiratory phase-specific activation was assessed in anesthetized, tracheotomized, spontaneously bre athing piglets. Negative pressure and flow applied to the isolated UA at ro om or body temperature during inspiration only enhanced posterior cricoaryt enoid muscle activity from that present without UA pressure and flow (basel ine) by 15-20%. Time shifting the onset of UA flow relative to tracheal flo w decreased this enhancement. The same enhancement was observed with oscill atory or constant airflow. UA positive pressure and flow at room or body te mperature applied during expiration only enhanced thyroarytenoid muscle act ivity from baseline by 50-160%. The same enhancement was observed with osci llatory or constant airflow at body temperature. Constant positive pressure and flow enhanced thyroarytenoid muscle activity more than oscillatory pre ssure and flow at room temperature. We conclude that the respiratory modula tion of UA afferents is processed in a phase-specific fashion and is depend ent on stimulus modality (tonic vs. phasic).