acting on nicotinic receptors for muscle contraction [85]. The motor nuclei for all three muscles are in the nucleus ambiguus with somatotopic organization [86]. Sympathetic neural supply is also present, but its role in motor events is unclear [80].
Functional motor activity
The UES has a resting pressure that keeps the lumen closed to separate the atmospheric pressure above from the negative intrathoracic pressure below and to prevent esophagopharyngeal reflux. Cessation of tonic vagal excitation of the UES initiates relaxation; the UES is pulled open by the hyoid bone moving upward and forward during swallowing, and sphincter opening ends when pharyngeal contraction arrives at the UES [59]. The sphincter relaxes either with a voluntary swallow or involuntarily during belching and vomiting to permit orad movement of content. In addition, a “pharyngeal swallow” that involves the pharynx, UES, and esophageal body can be initiated by pharyngeal stimulation [13].
Basal pressures
Tonic vagal excitation ensures significant but variable resting pressure in the closed UES [87], between 35 and 200 mmHg [79,88–90]. UES resting pressure is inconsistent due to its odd shape (see Figure 5.7). Further, reliable pressure measurements are difficult since the UES can move 2–3 cm during swallowing [79, 91], and the recording device itself may contribute to the measured pressure [87, 92, 93], with larger devices recording higher pressures [94, 95]. UES resting pressure decreases during sleep [96] and with anesthesia [97], which can reduce UES pressure to as low as 8 mmHg. UES pressure is higher during inspiration [92, 96,98–100], with coughing [101], and with stress [102, 103]. A number of reflex responses alter UES pressure, particularly to prevent reflux into the pharynx [104]. Pharyngeal HRM has improved the ability to monitor UES pressures and response during physiologic events such as swallowing and belching (see Figure 5.6).
Figure 5.5 Normal oropharyngeal swallow. (A) At rest the bolus is held in the mouth. (B) Bolus is conveyed into the oropharynx. The airway and surrounding larynx have been elevated. (C) Bolus is descending in advance of the descending peristaltic wave. The epiglottis is now horizontal, the larynx is maximally elevated, and the bolus passes into the hypopharynx. (D) Bolus continues to descend and begins to pass through the open upper esophageal sphincter (UES) into the esophagus, with the peristaltic wave descending behind it. The nasopharynx begins to open, and opening progresses in a descending sequence. (E) The pharyngeal contraction moves into the hypopharynx as the bolus continues through the open UES. The nasopharynx continues to open from the top. (F) Bolus is completely in the esophagus. The nasopharynx, pharynx, and entry to the airway have opened, although the larynx has not completely descended to its original position.
Source: Donner et al. [58] with permissions of Springer Nature.
Swallowing
The UES “relaxes” with SPG‐controlled cessation of tonic vagal excitation, with a decrease in UES pressure within 0.2 s of swallow initiation [105]. The UES opens about 0.1 s later when it is pulled by the hyoid bone moving upward and forward during swallowing [91, 106]. The degree of opening is higher with larger boluses because of the higher intrabolus pressure generated by tongue thrust and descending pharyngeal contraction [67, 74, 77, 105]. UES opening is synchronous with laryngeal vestibule closure, both occurring earlier with a larger bolus despite similar pharyngeal propagation velocity. Augmentation of UES opening can be achieved with forceful voluntary prolongation of laryngeal excursion, termed the Mendelsohn maneuver [107]. Concurrent with arrival of the descending pharyngeal contraction, the UES closes just prior to the laryngeal vestibule opening [71].
The 1 s oropharyngeal swallowing stage includes only about 0.5 s of UES opening [75]. Oropharyngeal dysphagia can occur if the sphincter fails to open adequately when the UES is hypertrophic and/or fibrotic with a “cricopharyngeal bar” on videofluoroscopy [106]. Paralysis or weakness of oropharyngeal musculature following stroke or Parkinson’s disease can compromise pharyngeal bolus [108–111] and/or prevent hyoid movement that opens the UES.
Figure 5.6 Upper esophageal function by high‐resolution manometry. The left side of the figure shows the high‐resolution picture of the timing and pressures of a swallow event, with upper esophageal (UES) and lower esophageal sphincter (LES) relaxation. (A) Typical UES relaxation and opening with a swallow, and its closure with the arrival of the pharyngeal contraction that then propagates through the striated portion of the upper esophagus. (B) UES opening during belching. During a transient LES relaxation (TLESR), a common gastroesophageal cavity develops that leads to UES opening and gas venting. A pharyngeal contraction is absent.
Source: Reproduced from Kahrilas PJ, Pandolfino JE. Esophageal motor function. In: Yamada T, ed. Textbook of Gastroenterology, 5th ed.Hoboken, NJ: Wiley‐Blackwell; 2008.
Figure 5.7 Three‐dimensional pressure profile of the upper esophageal sphincter (UES). The pressures are higher in the anterior and posterior positions and lower on the sides. UESP, UES pressure.
Source:Welsh RW, Gray JE. Influence of respiration on recordings of lower esophageal sphincter pressure in humans. Gastroenterology1982; 83:590–594. © 1982, American Society for Clinical Investigation. Published by Elsevier Inc. All rights reserved.
Esophagopharyngeal reflexes
The UES is highly responsive to a number of pharyngeal and esophageal events that either increase UES pressure or relax the sphincter. These reflexes, mediated by vagal afferents, protect the airway from esophageal content or release esophageal content during belching or vomiting [17, 46, 104, 112].
Esophageal distention with air, liquid, or balloons can either increase or decrease UES pressure, depending on the volume and rapidity of distention [101, 112]. Slow distention causes a protective augmentation in UES pressure [112, 113]; the pressure is augmented as distension increases [78, 114], and with closer proximity to the UES [112, 115]. Rapid distention and large distension volumes result in UES relaxation, with glottis closure and esophageal belching when air is introduced [116, 117]; there is a linear correlation between duration of UES relaxation and the volume of air introduced. The belch is also associated with glottic closure. UES relaxation also occurs with vomiting, a gastric belch, and rumination.
Acid in the esophagus increases UES pressure, with more profound increases when acid is infused closer to the UES or at the UES [112, 114, 118], but this reflex may be less prominent in humans compared to dogs, especially patients with esophagitis. Infusion of acid 5 cm below the UES in normal subjects [119], and acid reflux into the distal esophagus in normal subjects and in patients with esophagitis, did not increase UES pressure [120]. Increases in intrathoracic pressure with gagging or Valsalva maneuver increase UES pressure.