The esophagus acts as a conduit for the aboral transport of food from the mouth to the stomach. The three structural components of the esophagus are the upper esophageal sphincter (UES), the esophageal body, and the lower esophageal sphincter (LES ) [3]. The UES is physiologically defined as a zone of high intraluminal pressure between the pharynx and the cervical esophagus, which comprises the functional activity of three adjacent striated muscles, creating a tonically closed valve and preventing air from entering into the gastrointestinal tract. The main functions of the UES are to provide the most proximal physical barrier of the gastrointestinal (GI) tract against pharyngeal and laryngeal reflux during esophageal peristalsis and to avoid the entry of air into the digestive tract during negative intrathoracic pressure events, such as inspiration. The UES relaxes both transiently during swallowing, in order to allow the entry of a bolus into the esophagus, and during belching and vomiting, in order to allow the egress of gastric contents from the esophageal lumen. The UES is present by at least 32 weeks of gestation and is functional at birth [4]. However, swallowing coordination may be poor in the first week of life and in premature infants <1500 g [5, 6]. Structurally, the UES is ~0.5–1 cm long at birth and increases in length to ~3 cm in the adult [3].

The LES is the high pressure zone composed entirely of smooth muscle which maintains a steady baseline tone to prevent retrograde movement of gastric content into the esophagus. During swallowing and belching, the LES promptly relaxes in order to allow the passage of ingested food or air in appropriate directions. At the time of swallowing, the LES relaxes promptly in response to the initial neural discharge from the swallowing center in order to minimize resistance to flow across the esophagogastric junction. This relaxation starts within 2 s after the peristaltic contraction has begun in the proximal esophagus and lasts 5–10 s until the peristaltic wave reaches the distal esophagus. During relaxation, LES pressure falls to the level of gastric pressure. As the LES relaxes (an active process), it is passively opened by the bolus propelled by the peristaltic wave. The LES relaxation is followed by an after-contraction of the upper part of sphincter, which likely represents the end of contraction wave as it reaches the distal esophagus. Swallow-induced LES relaxation is part of primary peristalsis. Like the UES, LES length increases with age, from 1 cm in the newborn to 2–4 cm in the adult. LES pressure also varies with age, going from 7 mmHg in a premature infant of 27 weeks gestation to 18 mmHg at term and from 10 to 45 mmHg in adults [7, 8].

The body of the esophagus is similarly composed of two muscle types. The proximal esophagus is a predominantly striated muscle, while the distal esophagus and the remainder of the GI tract are composed of smooth muscle. The mid-esophagus contains a graded transition of striated and smooth muscle types. The muscle is oriented in two perpendicular opposing layers: an inner circular layer and an outer longitudinal layer, known collectively as the muscularis propria. The longitudinal muscle is responsible for shortening the esophagus, while the circular muscle forms lumen-occluding ring contractions.

The muscle layers contract simultaneously and produce peristalsis. Peristalsis is a sequential, coordinated contraction wave that travels the entire length of the esophagus, propelling intraluminal contents distally to the stomach. The LES relaxes during swallows and stays opened until the peristaltic wave travels through the LES and then contracts and redevelops resting basal tone. Peristalsis is divided in three phases.

The primary peristalsis is the peristaltic wave triggered by the swallowing center. The peristaltic contraction wave travels at a speed of 2 cm/s and correlates with manometry-recorded contractions. The secondary peristaltic wave is induced by esophageal distension from the retained bolus, refluxed material, or swallowed air. The primary role is to clear the esophagus of retained food or any gastroesophageal refluxes. The tertiary contractions are simultaneous, isolated, and dysfunctional contractions. These contractions are non-peristaltic, have no known physiologic role, and are observed with increased frequency in elderly people.

High-resolution manometry (HRM ) was developed to increase interpretative consistency and diagnostic accuracy of esophageal manometry [9, 10]. In contrast to conventional manometry, HRM has two minimum requirements that improve spatiotemporal resolution: recording sites that are positioned closely enough (usually at 1 cm intervals) to allow accurate interpolation of data between sites and an appropriate computer system for acquisition of the data and creation of the desired three-dimensional plots [9]. Axial interpolation has already proved useful in understanding the correct relationship of pressure data when unusual wave forms occur, for example, multi-peaked waves [10]. Three-dimensional topographical plots are convenient methods of visually representing the large amount of data provided by the increased number of recording sites (Fig. 7.1).

On a theoretical level, HRM provides advantages over conventional techniques for the assessment of esophageal function. One of the most important advantages of HRM is that it makes diagnostic esophageal manometry easier and quicker to perform. It takes away the need for a pull-through and precise positioning of the manometric catheter with respect to the LES. A lab technician or nurse can thus simply perform HRM, and only limited experience in esophageal manometry is required. The pattern of esophageal peristalsis and sphincter activity defines whether esophageal motor activity is normal or abnormal. The intrabolus pressure and esophagogastric pressure gradient define whether or not this activity is consistent with effective function. On a practical level, HRM makes it easy to acquire good quality pressure measurements from the esophagus, facilitates positioning of the catheter, and removes the need for a pull-through procedure. Moreover, spatiotemporal plots of pressure information make it easy to identify normal and abnormal patterns of esophageal motility [11].

A manometric apparatus consists of a pressure sensors and transducers combination, which detects the intraluminal pressure and changes it into an electrical signal, and a recording device to amplify, record, and store that electrical signal. Although each component can potentially affect recording fidelity, most attention is rightfully focused on the pressure sensor and transducer combination. Recorders (whether they are ink-writing polygraphs, thermal writing polygraphs, or computers with analogue to digital converters) all possess response characteristics far in excess of that required for recording esophageal pressure complexes.

Three types of data display can be generated and are available for review immediately after completion of the recording sessions, each taking into consideration both time and space relationships of manometric data. Surface plots are three-dimensional representations examined from different elevations or perspectives; contour plots represent three-dimensional data in a single “overhead” perspective as is commonly used to display geographic or weather data; and axial transformations represent data at a single time across all of the recording channels, the dimension of time being represented by an animation of the data frames. In all cases, the initial step involves alignment of the manometric data on a planar surface [9].

The surface plots are created by exporting three-dimensional data sets to a program specifically designed for geographic mapping. The developed system creates x, y, z data sets for specified time intervals following designated event markers inserted during analysis. For these data sets, x represents the recording site position on the catheter in cm, y the time after the event marker in seconds, and z the pressure amplitude at that time and location in mmHg. In creating surface plots, a grid of data is first established, the gridline interval being determined by the investigator for both the x and y directions. For the purposes of esophageal plotting, gridlines are usually positioned at 0.2 cm and 0.2 s intervals. The z value (pressure amplitude) is interpolated at each grid intersection using available neighboring data for establishing the most appropriate value. Resultant plots can be tilted forward or rotated as required to best visualize the three-dimensional data [9]. Contour plots represent an overhead perspective of surface plots, each contour ring encircling amplitudes of equal or greater value than that specified on the color legend. A series of concentric rings indicates a regional pressure peak on the plot. In the developed system, the plot baseline can be shifted as required for zero adjustment (e.g., to match intragastric pressure). Likewise, the first contour level as well as the pressure interval for subsequent rings can be modified as required. The axial transformations of manometric data are available only on the developed system. Individual frames are created by splining data across all recording sites at a specified time following an inserted or adjusted event marker. All frames are then viewed as an animated movie, the animation speed adjusted by the investigator (Figs. 7.1 and 7.2) [9].

Two basic varieties of manometric systems (water-perfused and solid-state systems) are now available to perform HRM. Each design has distinct advantages and disadvantages.

The water-perfused catheters for HRM with 21–32 channels and, more recently, up to 36 pressure sensors contain smaller lumina, which are perfused at very low rates. In children, at least 80 % of the esophageal body and one sphincter could be sampled with the catheter with 21 lm in either a proximal or distal recording position. With this design, a 20 cm segment is sampled simultaneously. Data acquired by HRM can be analyzed and presented either as multiple line plots or as a spatiotemporal plot. In water-perfused systems, pressures are transmitted along a column of water to external transducers. This makes the catheters more flexible and cheaper but more unwieldy to use as the water perfusion pump must be set up and the dynamic fidelity of the system is damped by the compliance of the water perfusion system.

With water-perfused systems , a pneumohydraulic pump perfuses distilled water through the lumens of the multilumen manometric catheter. Each lumen is connected to an external volume displacement pressure transducer and terminates at a side-hole or sleeve channel within the esophagus, sensing the intraluminal pressure at that position by the relative obstruction to the flow of the perfusate. In addition to having well-defined, time-tested response characteristics, other advantages of the perfused manometric system are: 1) low cost; 2) easy availability of 8 lm extruded polyvinyl tubes that can be made into manometric assemblies of varied sensor configuration; 3) compatibility with sleeve devices for assessing sphincter function, and 4) temperature stability. Disadvantages of perfused manometric systems are as follows: 1) Proper equipment maintenance, which is essential for the system to achieve published response characteristics, requires relatively skilled personnel; 2) recording characteristics are unsuitable for accurate pharyngeal studies [7].

Differently from water-perfused system, in the solid-state system, the pressure transducers are incorporated into the catheter itself. This makes the pressure rise rate high, particularly where pressure changes are rapid (e.g., the pharynx).

The main alternative to the water-perfused manometric system is a manometric assembly incorporating strain gauge sensors and solid-state electronic elements. In these manometric systems, the manometric probe contains the transducers at fixed locations along its length. The probe plugs into a small box containing the electronic elements, connected to the recorder. The advantages of intraluminal strain gauge systems are their vastly expanded frequency response, making them suitable for recording any intraluminal pressure activity, and their less cumbersome nature compared with perfusion pumps, requiring less skilled personnel to perform clinical studies and less equipment maintenance. The main disadvantages are as follows: the manometric probes are expensive, sometimes fragile, and unmodifiable; manometric probes are subject to several physical constraints with respect to the number of sensing elements and the proximity of the elements to each other; and there is no equivalent of a sleeve device compatible with this system [7].

With either system, the spacing of the sensing ports depends on the size of the patient. The interval between perfusion ports or transducers may need to be as close as 1–3 cm apart to accommodate the shorter esophagus in infants. During perfusion in infants and small children, the perfusion rate may need to be lower because of the size of the esophagus, the fluid tolerance of infants, and the potential for aspiration. Care must be exercised to compensate for the slower flow rate by decreasing the system compliance [2].

Because of the differences in size of the esophagus, cooperation by the patient, and neurologic and developmental maturation, HRM is performed differently in children than in adults.

Esophageal HRM is best performed without sedation. In many children, however, sedation is necessary. Midazolam and chloral hydrate have been shown to be effective with minimal or no influence on pressure measurements [12, 13]. A natural reflex swallow may be induced in young infants and neurologically abnormal children by gently blowing in the child’s face (Santmyer swallow) [14].

The single most difficult technical aspect of esophageal manometry in children is cooperation. Physicians performing manometry in children must have great patience, and the study needs to be performed by experienced staff and a supportive parent/guardian. The patient’s cooperation can, however, be improved by the use of age-appropriate relaxation techniques. For example, infants relax with swaddling and use of a pacifier. Toddlers are comforted having a favorite blanket or toy. School-age children benefit from being allowed to handle and examine equipment before the procedure. Adolescents benefit from a thorough review of what to expect before the procedure. Recording artifacts are common in the pediatric patient and occur more commonly than in adults. Specific behaviors (e.g., crying or squirming) should be noted on the tracing itself to allow proper interpretation upon completion of the study [2].

Catheter size has a significant impact on tolerance. Currently standard HRM catheter size is 12.5 French, and with this catheter size we would be very reluctant to perform a study in a child under 7 kg. Once the catheter is in position, children will usually (within 5–10 min) become accustomed to the catheter. However, they may resist swallowing of boluses or may not swallow on command particularly if cognitively impaired. When children do not swallow on command, techniques such as cervical auscultation or palpation of the throat can be used to assist in marking the primary swallow. A natural reflex swallow may be induced in young infants and neurologically abnormal children by gently blowing in the child’s face.

The following protocol is recommended:

Despite the technical advances, considerable time and expertise are required to obtain a technically adequate and maximally informative study of esophageal function by this technique. At present, abnormal motor activity as measured by “conventional manometry” is defined in terms of a few basic patterns: incomplete sphincter relaxation, esophageal spasm, hypertensive contractions, and loss of tone and motility [11, 15, 16]. This classification is simple; however, even for experienced physiologists in specialist centers, interobserver agreement in the interpretation of manometric measurements is poor [17]. Only achalasia and severe diffuse esophageal spasm are specific disorders with manometric abnormalities that are absent in healthy subjects. Other esophageal motility disorders are poorly defined, often include “abnormalities” that can be found in symptom-free individuals as well [18, 19] and are inconsistent over time [20].

One important observation made in adults that accentuates the value of HRM is that esophageal peristalsis is comprised of a specific chain of sequential pressure segments (Fig. 7.2). These segments, one in the striated muscle region and two in the smooth muscle region, appear as concentrated pressure loci separated from each other by lower amplitude pressure troughs on the three-dimensional maps [21–25].

Staiano et al. reported that the same chain of pressure segments identified previously in adults was recognized in every child with the exception of seven with aperistalsis, six of whom were ultimately diagnosed as having achalasia [22]. The first and second pressure troughs were similarly distributed across esophageal length in each age group, but the third trough was located proportionately less closely to the upper margin of the resting LES in the neonates compared with infants/toddlers or children [22]. The first pressure segment was more consistently present in children than in the other two age groups, and the percentage of swallows with the third pressure trough was decreased in neonates compared with children. Consequently, completely formed peristaltic chains were less commonly observed in the neonates, but the number of subjects was too small to confirm that this was a clinically meaningful finding [22]. No differences were found in the presence or distribution of the pressure segments within the esophageal body in subjects who had symptoms ultimately attributed to esophageal disease or who had other explanations for the presenting complaints.