The process of swallowing is a complex phenomenon involving the passage of the bolus from the mouth into the oesophagus and a temporary transformation of the airway into a gastrointestinal tract.4 The process involves motor and sensory structures and involves three distinct phases: an oral, voluntary phase in which the bolus is prepared and propelled into the pharynx5; a pharyngeal involuntary phase in which the temporary transformation of the oropharyngeal structures takes place, allowing the bolus to pass into the oesophagus via the upper oesophageal sphincter (UOS)1, 2; and an oesophageal involuntary phase, which accompanies the bolus into the stomach.3

The pathophysiology of the impaired safety is related to a delay in the activation of several physiological reflexes aimed at pharyngeal reconfiguration from airway to gastrointestinal tract, resulting in a slow neural swallowing response. Failures to swallow safely in OD patients are associated with an increased risk of aspiration and respiratory penetration with the risk of aspiration pneumonia6, 7 and failures in efficacy are related to impaired bolus transport due to decreased pharyngeal propulsive force or altered UOS opening, with the presence of residual food in the oropharynx and increased risk of malnutrition and dehydration.8 Some of the most common causes are pathophysiological changes associated with ageing and neurodegenerative and pharmacological diseases.2

The UOS is a high-pressure anatomical region at the pharyngoesophageal junction about 3−4 cm in length, comprising the lower pharyngeal constrictor, cricopharyngeus and cervical oesophageal striated muscles.9 The cricopharyngeus is located in the transition zone between the lower pharyngeal constrictor and the cervical oesophageal musculature, and the area of greatest pressure is in the upper region, which is anatomically bound by muscle tissue, cartilage and aponeurosis rather than a simple muscular ring.

Histologically, the cricopharyngeus is a striated muscle of small, slow-twitch type I fibres, not set in parallel, which allows basal tone to be maintained.9 The presence of some fast-twitch fibres allows rapid contraction during swallowing, belching and vomiting. Relative to other skeletal muscles, the cricopharyngeus has a large proportion of connective tissue.

The UOS is closed in the resting state and the following four phenomena are necessary for it to open: 1) interruption of vagal tone over the cricopharyngeus, allowing muscle relaxation; 2) anterior sphincter traction caused by hyoid muscle contraction; 3) propulsive forces of the tongue and pharynx on the bolus; and 4) sphincter compliance allowing complete relaxation, low residual pressures and absence of resistance during swallowing.10

The alterations in the mechanisms described above give rise to three major pathophysiological patterns of UOS dysfunction: a) restrictive change in flow at the UOS, where propulsive capacity at the base of the tongue and pharynx will be normal but with altered relaxation of the UOS due to neurological disease (central or spastic, such as Parkinson’s disease) with inability to interrupt the vagal tone on the cricopharyngeus, or isolated at the UOS with alteration of its compliance, as in the case of cricopharyngeal bars; b) weakness in the contraction of the hyoid musculature or the base of the tongue, secondary to neurodegenerative disease or sarcopenia with normal relaxation of the UOS; and c) mixed processes with both altered relaxation of the UOS and altered propulsive capacity of the tongue and pharynx, for example, in patients with previous radiotherapy treatment.11, 12

The aim of diagnosis in OD is for a multidisciplinary team to assess swallowing efficiency and safety early, using clinical screening methods, such as medical history, specific questionnaires and validated clinical methods (for example, Volume-Viscosity Swallow Test [V-VST]). Subsequently, patients in whom abnormalities are detected in the validated clinical methods should have instrument-based assessment with videofluoroscopy (VFS) or assessment of swallowing by laryngoscopy (Fiberoptic Endoscopic Evaluation of Swallowing — FEES). Tests may then be supplemented with high-resolution pharyngoesophageal manometry (HRPM).

The main aims of this article are to review the current accepted methodology for performing and interpreting HRPM; to provide guidelines for classifying the different patterns of UOS dysfunction using HRPM; and to be able to decide the most appropriate treatment for each patient.