Impaired opening of the UES can cause partial or even total obstructionof the food passageway, with retention in the piriform sinuses and hypo-pharynx, increasing risk of aspiration after the swallow. Insufficient UESopening can be caused by increased stiffness of the UES, as in fibrosis orinflammation, or by failure to relax the sphincter musculature, as noted ear-lier. Weakness of the anterior suprahyoid muscles can impair opening of theUES, because these muscles normally pull the sphincter open duringswallowing.

Esophageal dysfunction is common and often asymptomatic. Esophagealmotor disorders include conditions of hyperactivity (eg, esophageal spasm),hypoactivity (eg, weakness), or incoordination of the esophageal muscula-ture [47]. Any of these conditions can lead to ineffective peristalsis, withretention of material in the esophagus after swallowing. Retention can resultin regurgitation of material from the esophagus back into the pharynx, withrisk of aspirating the regurgitated material. Esophageal motor disorders aresometimes provoked by gastroesophageal reflux disease and, in some cases,can respond to treatment with proton pump inhibitors.

Airway protectiondpenetration and aspiration

Airway protection is critical to swallowing, and its failure can haveserious consequences. Laryngeal penetration occurs when passage of thematerial transported from the mouth or regurgitated from the esophagusenters the larynx above the vocal folds. In contrast, aspiration is definedas passage of material through the vocal folds (Fig. 9). Laryngeal penetra-tion is sometimes observed in normal individuals. Aspiration of microscopic

Fig. 9. Videofluorographic images of (A) laryngeal penetration and (B) aspiration in dysphagic

individuals swallowing liquid barium. Arrows indicate the leading edge of the barium in the

airway.

704 MATSUO & PALMER

quantities also occurs in normal individuals; however, aspiration that isvisible on fluoroscopy or endoscopy is pathologic and associated with in-creased risk of aspiration pneumonia or airway obstruction [48]. Aspirationcan occur before, during, or after swallowing. Clinicians should consider themechanism of aspiration when it is observed on fluoroscopy or endoscopy.Impairments of airway protection can result from reduced hyolaryngealelevation, impaired epiglottic tilt, incomplete closure of the laryngeal vesti-bule, or inadequate vocal fold closure due to weakness, paralysis, or ana-tomic fixation. These impairments can lead to aspiration, usually duringthe swallow. Aspiration before the swallow is commonly caused by prema-ture entry of liquids into the pharynx (due to impaired containment in theoral cavity) or by delayed onset of laryngeal closure after a bolus is pro-pelled into the pharynx. Aspiration after the swallow is usually due to accu-mulated residue in the pharynx after the swallow. Material may be inhaledwhen breathing resumes after the swallow.

The consequences of aspiration are highly variable, ranging from no dis-cernable effect to airway obstruction or severe aspiration pneumonia. Thenormal response to aspiration is strong reflex coughing or throat clearing;however, laryngeal sensation is often abnormal in individuals who havesevere dysphagia [49]. Silent aspiration, or aspiration in the absence of vis-ible response, has been reported in 25% to 30% of patients referred for dys-phagia evaluations [49–51]. Several factors determine the effect of aspirationin a given individual, including the quantity of the aspirate, the depth of theaspiration material in the airway, the physical properties of the aspirate(acidic material is most damaging to the lung, producing chemical pneumo-nitis), and the individual’s pulmonary clearance mechanism [52]. Poor oralhygiene can increase the bacterial load in the aspirate, increasing the riskof bacterial pneumonia.

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