The classic method to evaluate the LES is with stationary manometry using a slow motorized pull-through technique. With this technique all three critical components of the LES can be evaluated. These components interact and are codependent to maintain the competency of the LES. On stationary manometry a structurally defective valve is defined as one with a resting pressure below 6 mmHg, an overall length less than 2 cm, or an intra-abdominal length less than 1 cm [2] (Table 7.1).

An abnormal value for any component can make the valve incompetent, and the likelihood of an incompetent valve increases when more than one component is abnormal [3]. Failure of these three interdependent factors to maintain an adequate resistance at the LES leads to free reflux of gastric juice into the esophagus.

Competency of the LES is a function of pressure and length. Low resting pressure is the most common abnormality reported by most laboratories. However if careful attention is paid to length, the most common abnormality of the LES is actually a short intra-abdominal length. The abdominal length of the LES is critical because studies have shown that below a minimum abdominal length of 1 cm there is essentially no pressure that will allow the LES to remain competent [4]. Using a specially designed catheter and a three-dimensional computer construct, LES resistance can be represented as a volume diagram. This is called the “Sphincter Pressure Vector Volume” (SPVV) and a calculated volume of less than the fifth percentile of normal indicates a defective LES [5] (Fig. 7.4).

High-resolution manometry has become widely accepted for the evaluation of the esophageal body and has replaced water perfusion methods. Unfortunately, while it has enhanced many aspects of esophageal manometry, it is unable to give an accurate portrayal of the length of the LES, and as such a detailed understanding of the LES is not possible. This deficit is being addressed with new technology, entitled high-definition manometry. This technology will once again allow detailed assessment of the length and vector volume of the LES. Other tests that are useful for esophageal evaluation offer limited insights into the LES, including upper endoscopy, CT scans, and barium esophagrams.

The purpose of the LES is to maintain a barrier between the acid-sensitive esophageal squamous mucosa and the acid-secreting gastric mucosa. Without this barrier gastric contents would follow the natural pressure gradient from the positive pressure environment of the abdomen towards the negative pressure of the intra-thoracic esophagus. In its resting state, the LES maintains a pressure of 13–43 mmHg, and given that a portion of the sphincter is within the abdomen it can compensate for sudden increases in intra-abdominal pressure that occur with straining, coughing, or bending over. In addition to maintaining a barrier, the LES must also relax to allow a bolus of food or liquid to enter the stomach, and to allow gas and sometimes gastric contents to vent upwards as a belch or as emesis when necessary. The tonic resting pressure of the normal LES and deglutitive lower esophageal sphincter relaxation (DLESR) with a swallow is nicely seen with high-resolution esophageal manometry (Fig. 7.5). At the start of a swallow, the UES opens to allow a bolus to move from the pharynx into the cervical esophagus. Tactile stimulation of the striated muscle of the pharynx stimulates the vagus nerve, which in turn stimulates the LES to relax. Relaxation of the LES should coincide with UES opening and persist until the bolus passes through into the stomach. Once the bolus passes through the LES there is a post-relaxation contraction after which the LES returns to its basal resting pressure. From start to finish the entire LES relaxation usually lasts about 8–10 s.