Fig. 5.
Schematic presentation of key factors for normal pharyngeal function and airway protection and the impact of morphine (A) and midazolam (B). Oral coordination, (prevents premature leakage of oral contents into the pharynx); coordination of pharyngeal contraction wave (the propagation of contractions in the pharyngeal constrictor muscles into the UES); pharyngeal muscle contraction forces (increased pharyngeal pressures moves bolus caudally during swallowing); pharyngeal clearance (prevents retention of pharyngeal residue after completion of the pharyngeal contraction wave); UES (resting pressure in the UES contributes to airway protection by preventing aerophagia and regurgitation); laryngeal protection (prevents penetration of contents to laryngeal inlet and aspiration); frequency of spontaneous swallowing (prevents accumulation of bolus in the pharynx); latency to swallow (response time to initiate swallowing); coordination of breathing and swallowing (swallowing during expiration and normal duration and timing of apnea in relation to the pharyngeal phase of swallowing prevents aspiration). UES = the upper esophageal sphincter.