A Matter of Degree:
When a bolus moves past the base of the tongue and downward into the pharynx during a swallow, the normal path is toward the esophagus. However, if the bolus enters the glottis (opening to the trachea) and moves as far as the vestibule above the true vocal folds, this is termed “penetration”. The detour of the bolus may take a very short trip or last a very short time before correcting course, in which case the penetration may be called a “flash penetration”. Penetrated boluses may trigger sensations from the vestibular walls prompting coughing or choking responses or a tickling sensation as a protective measure. These signs can be clinical indicators of risk for aspiration. The superior laryngeal branch of the recurrent laryngeal nerve bilaterally supplies this sensory innervation.
Aspiration takes place when the bolus actually passes through the true vocal folds, breaching airway protection usually provided by normally functioning true vocal folds. The aspirated bolus can move on downward in the trachea, tending to eventually find its way to the lowest position within the lung. That position is typically the right lower lobe of the lung because the path to the right lung is less acute (the left bronchus must exit more acutely from the trachea to arch over the heart) and because most persons are sitting or standing upright.
If the patient is lying
more often in bed, then the lowest point in the lungs may be in the middles
lobes, posteriorly. Therefore, it is important
to note the habitual positioning of the patient when attempting to interpret
chest x-rays when possible aspiration pneumonia is diagnosed. Aspiration
pneumonia develops as microorganisms, usually bacteria, grow on the residue
in the lungs and lead to infection.
If the primary care provider sees a patient with pneumonia, it would be prudent to consider sending a consult to a Speech Language Pathologist (SLP) to rule out aspiration as an etiology. If a patient is showing clinical signs such as coughing or swallowing, the patient may be penetrating, but not necessarily aspirating, food or liquids. It is important for the SLP to differentiate and diagnose penetration or aspiration.