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Departments of 1 Physiology and 2 Pediatrics, Medical College of Wisconsin and Zablocki Veterans Affairs Medical Center, Milwaukee 53226; and 3 Department of Physical Therapy, Marquette University, Milwaukee, Wisconsin 53201
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 (UAWSG) area. During eupnea in nine goats with intact UAW, the TP and HP were active during expiration, whereas the SP exhibited tonic expiratory and phasic inspiratory activity. After mechanically induced apneas (MIA), TP activity increased (263%, P < 0.02), HP activity exhibited a small, varied response, and SP activity greatly decreased (10%, P < 0.02). During resumption of respiratory effort, all goats exhibited absent/reduced airflow, and when diaphragm activity was 95% of control, TP activity remained elevated (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 activity increased (P < 0.02). After MIA in six goats with isolated UAW, TP activity increased 198% (P < 0.02) and UAWSG area (endoscopically determined) decreased (to 15% of control, P < 0.02). During recovery from MIA, a correlation was found between UAWSG 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 UAWSG area, and an imbalance in activity of these opposing muscles can lead to UAWSG narrowing.
hypocapnia; hypercapnia; central apnea; pharyngeal muscles; laryngeal muscles; airway obstruction; electromyography; endoscopy
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