Reciprocal activation of hypopharyngeal muscles and their effect on upper airway area

We examined in awake goats, 1) with intact upper airways (UAW), the effect of altering chemical drive on pharyngeal constrictors [thyropharyngeus (TP) and hypopharyngeus (HP)] and a dilator [stylopharyngeus (SP)], and 2) with an isolated UAW, the effect of activation of these muscles on supraglottic UAW (UAW(SG)) area. During eupnea in nine goats with intact UAW, the TP an d HP were active during expiration, whereas the SP exhibited tonic expirato ry and phasic inspiratory activity. After mechanically induced apneas (MIA) , TP activity increased (263%, P < 0.02), HP activity exhibited a small, va ried response, and SP activity greatly decreased (10%, P < 0.02). During re sumption of respiratory effort, all goats exhibited absent/reduced airflow, and when diaphragm activity was 95% of control, TP activity remained eleva ted (135%) and SP activity was reduced (56%, P < 0.02). During hypercapnia, 1) TP activity decreased (P < 0.02), 2) HP response varied, and 3) SP acti vity increased (P < 0.02). After MIA in six goats with isolated UAW, TP act ivity increased 198% (P < 0.02) and UAW(SG) area (endoscopically determined ) decreased (to 15% of control, P < 0.02). During recovery from MIA, a corr elation was found between UAW(SG) area and the ratio of SP to TP activity. We conclude that the reciprocal activation of mechanically opposing dilator and constrictor muscles in the hypopharynx is correlated to changes in the UAW(SG) area, and an imbalance in activity of these opposing muscles can l ead to UAW(SG) narrowing.