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

Abstract

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 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 UAW(SG) area (endoscopically determined) decreased (to 15% of control, P < 0.02). During recovery from MIA, a correlation 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 lead to UAW(SG) narrowing.

Hypocapnia is associated with increased upper airway expiratory resistance during sleep

“…Conversely, hypocapnia, per se, independent of ventilatory drive could lead to pharyngeal narrowing. Evidence implicating hypocapnia per se includes activation of the pharyngeal constrictors and laryngeal expiratory muscles by hypocapnia (Feroah et al, 2000; Kuna et al,1993; Kuna and Vanoye, 1997; Praud et al, 1990; Sears et al, 1990) and the reduced tonic muscle activity under hypocapnic conditions in a feline preparation (Frankshtein and Sergeeva., 1983). Therefore, we hypothesized that hypocapnia per se would lead to expiratory pharyngeal narrowing during sleep independent of ventilatory motor output.…”

Contributions of the Kölliker–Fuse nucleus to coordination of breathing and swallowing

“…Is the primary response to chemical stimulation of the KFN with 10 µl IA the biphasic ventilatory response, and the occurrence of swallows simply follows as a function of breathing, perhaps for the purpose of increased mucociliary clearance concomitant with increased breathing? This possibility seems unlikely as there are other stimuli such as hypercapnia that increase breathing without affecting swallowing occurrence (Feroah et al, 2000). A second possibility is that there are changes in the sensitivity of the swallowing reflex that account for waxing and waning in the number of swallows, and that the pattern of swallow occurrence is parallel but mechanistically controlled independently from the biphasic ventilatory response.…”

The equine nasopharynx in dynamic upper airway disorders: an update

“…In normal awake goats, the stylopharyngeus muscle was found to exhibit tonic expiratory and phasic inspiratory activity, whereas the pharyngeal constrictors were active during expiration. This duality of action allows the nasopharynx to adapt its size and shape to the airflow and resist collapse when large negative pressures are applied to the upper airway (Feroah et al 2000).…”