Aspiration is defined as the entry of foreign material into the airway below the true vocal cords. In normal individuals, particularly infants and children, aspiration occurs when the airway protective mechanisms are stressed, such as while talking, laughing, eating, or sleeping. In most instances, an inconsequential amount of material is aspirated. In contrast, children with swallowing dysfunction are at much greater risk for pathologic aspiration. In these individuals, aspiration may result in acute or chronic pulmonary compromise, and impaired nutritional intake may lead to failure to thrive.
DEVELOPMENT OF FEEDING AND SWALLOWING
The swallowing mechanism goes through stages of maturation during infancy, beginning with suckling movements in utero and progressing to the development of chewing during early childhood [1,2]. Recognition of these developmental states informs the evaluation of swallowing disorders.
- Suckling, the earliest form of sucking, is characterized by a primitive anterior to posterior movement of the tongue. Suckling movements begin in utero with suckling and swallowing of amniotic fluid, and are the main form of feeding activity during the first four to six months of life. (See "Sucking and swallowing disorders in the newborn".)
- True suck is usually established by nine months of age.
- The ability to drink from a cup requires both sucking and swallowing, and is usually established by 12 months of age.
- Chewing patterns develop gradually during infancy, with the establishment of true chewing by 24 months of age.
Deglutition is another skill that develops as oropharyngeal structure and function mature. This process is typically divided into four phases: oral preparatory, oral, pharyngeal, and esophageal [1,2].
- The oral preparatory and oral phases, considered voluntary stages of swallowing, include receiving the food, forming the bolus, and transporting it posteriorly.
- The pharyngeal phase, also known as "reflex swallow," utilizes complex and coordinated muscle activity. During this phase, contraction of the pharyngeal musculature propels the bolus downwards and the larynx elevates and closes at the level of the epiglottis, mainly by closure of the aryepiglottic folds and vocal cords, to prevent laryngeal penetration and aspiration.
- The esophageal phase begins with the relaxation of the cricopharyngeal sphincter, which allows the bolus to pass through the esophagus.