“The upper oesophageal sphincter is a high-pressure zone, similar to a “nozzle” located in the pharynx, which acts as a barrier between the pharynx and oesophagus, preventing air from entering the digestive tract and preventing reflux from the oesophagus into the pharynx.
However, when high levels of reflux break through the high pressure zone of the upper oesophageal sphincter a different form of transpharyngeal spraying can occur, causing pharyngeal reflux and microaspiration into the trachea.”