Pressure measurement can also be combined with impedance measurement on some specialized catheters (Fig. 19.1). In this context, impedance refers to resistance to an electrical current. This can be measured by swallowing material that has an ionic charge, such as saline solution. As saline passes between impedance sensors, the electrical charge changes, and thus the data processor reflects that as a change in signal. Therefore, impedance manometry can measure pressures in relation to bolus flow during swallowing without the use of videofluoroscopy [13].

The catheter is placed transnasally into the pharynx and esophagus. Water-based lubricants are often used to assist in passage of the catheter, and a topical anesthetic applied to the anterior nasal passage is sometimes used in older children to reduce discomfort associated with the procedure. Videofluoroscopy or endoscopy can be used to guide catheter placement, but placement is often done blindly, relying on the pressure tracings to identify anatomic landmarks. When accurate catheter placement is confirmed, it can be secured to the nasal tip with adhesive tape, allowing the examiner to move freely. This is an advantage over endoscopy, in which close proximity between the clinician and the child must necessarily be maintained. This ability to move away from the child immediately after catheter insertion can facilitate acclimation to the catheter and subsequently improve the quality of the data obtained. Following placement, a short period of time is allotted for the patient to acclimate to the catheter before swallowing trials are begun. Patients are instructed to fast prior to the examination to reduce the risk of emesis during placement and so the patient is motivated to eat and drink during the procedure.

In both pediatric and adult esophageal high-resolution manometry studies, it is commonplace to follow a standardized protocol [14, 15]. However, no widely accepted protocol exists for pharyngeal high-resolution manometry. Liquids are more frequently used in the literature, with measured boluses ranging from 0.3 to 5 ml for children and bottle-feeding for infants. When possible, bolus trials should be administered methodologically with consistent volumes and consistent methods of delivery. Modifications in position, bolus administration, volume, liquid viscosity, and use of compensatory strategies should be trialed as necessary to answer the clinical question at hand. A benefit of high-resolution manometry over videofluoroscopic or endoscopic swallowing evaluations is that the bolus does not need to be modified (i.e., with barium or food coloring), allowing for a wide variety of foods and liquids that can be assessed during the evaluation. Additionally, once the catheter is in place, the patient may be positioned without much restriction.

There can be multiple indications for performing a pharyngeal high-resolution manometry study in a pediatric patient. The primary indication is when a clinical question cannot be answered through other swallowing evaluations. Specifically, those who aspirate, have unexplained pharyngeal residue, have suck-swallow-breathing discoordination, and have difficulty with solids or those with nasal regurgitation can particularly benefit from this procedure [4]. Pharyngeal swallowing pressures can also be assessed in the setting of esophageal dysphagia [5]. Patients with oral-only dysphagia are not likely to benefit from a transnasal high-resolution manometry study. It is common for the patient to undergo other evaluations of swallowing prior to receiving a manometric study, such as a clinical exam or an endoscopic or videofluoroscopic evaluation of swallowing [5, 16].

Risks of the procedure are often minimal and are similar to those with endoscopy. Practitioners must closely monitor the patient for signs of discomfort, gagging, emesis, epistaxis, laryngospasm, and a vasovagal response [17, 18]. Sedation and use of topical anesthetic should be used with caution, as it can impact participation and may interfere with pressure generation [5, 18]. Most of these risks resolve quickly on their own and can be avoided through use of lubricant, skilled placement, having the child fast prior to the procedure, and managing the child’s and family’s expectations. One must always assess the risk/benefit ratio when determining the appropriate course of evaluation.

In any assessment of feeding and swallowing in pediatric populations, the patient may refuse to comply. If it appears that the patient will be unable to complete prescribed tasks or if it appears that only a limited number of bolus trials will be completed, attempting to match authentic feeding patterns as closely as possible will provide the most meaningful data for description of the patient’s swallow function and for informing clinical decision-making. The clinician should keep in mind, however, that comparison to normative data will be invalidated when modifications to systematic swallow tasks are made. Crying, coughing, gagging, and even excessive movement can impart pressure artifacts in the signal, so care should be taken to make note when these events occur [5].

Data Analysis

Pressure representations are displayed in real time during the manometry examination. This can be used for online, qualitative analysis of the data. Gestalt observations can be made about swallowing pressure amplitude, duration, and coordination, and some systems allow for pausing of the data stream for finer-grained analysis. This display can also be used to educate patients and family about swallowing physiology, can serve as a biofeedback tool, and can be a distractor for the patient.

The power of high-resolution manometry, however, comes in the robust, objective data analysis that occurs after the study is completed. As there are no commercial hardware systems designed for pharyngeal high-resolution manometry, there are no software systems available either. Esophageal manometry software systems often can be modified to extract pressure variables of interest, and one can export raw pressure data for analysis in a third-party software, such as MATLAB (MathWorks, Natick, MA). Research teams have devised pressure and impedance analysis software for adult pharyngeal high-resolution manometry [13, 19], but no such software is currently validated for pediatric manometry.

High-resolution manometry data are first segmented into different regions of interest (Fig. 19.1). The velopharynx is a region of swallowing-related pressure that arises from velopharyngeal port closure and some contributions from the oral tongue to propel the bolus [7]. The tongue base receives pressure from tongue base retraction and pharyngeal wall contraction, and the hypopharynx is immediately inferior and sits around the laryngeal inlet [11]. Some publications group tongue base and hypopharynx together into the mesopharynx region [19]. The upper esophageal sphincter (UES) is defined by a region of elevated resting pressures that relax during swallowing [20]. As oropharyngeal swallowing is a dynamic process with many moving structures, there is a subset of manometry sensors that register pressures while the UES is at an elevated position [21]. High-resolution manometry analysis benefits from the multi-sensor assessment of pressures along the continuum of the pharynx.

Once the data stream has been segmented into different regions of interest, it can be analyzed according to pressure amplitudes and timing. The measures obtained can help the clinician to describe gestalt strength of the pharynx, relative ability of given segments of the pharynx and UES to generate pressure, and ability of the individual to create pharyngeal pressure differentials necessary for propagation of the bolus from the oropharynx to the esophagus efficiently [22]. See Table 19.1 for a description of pharyngeal and UES pressure parameters reported in pediatric pharyngeal high-resolution manometry. In the pharynx, simple maximum pressures and pressure durations are reported most commonly [23–25]. In the UES, relaxation minimum (nadir) pressures and relaxation duration describe the relative ease through which a bolus could pass through the UES [23, 26]. Although most high-resolution manometry systems average pressures circumferentially or measure pressure unilaterally from the posterior aspect, a large proportion of pharyngeal and UES pressures come from anterior and posterior directions, with less of a contribution laterally [10, 11]. In addition to pressure minima/maxima, some research groups use contractile integral [25] or area under the pressure curve. Pressure integrals may be more descriptive than pressure maxima, as it is measured throughout the entire pressure wave and is a composite measure of the total pressure generated. Pressure velocity and timing between certain pressure events have also been described [4, 22]; these parameters may be more descriptive of pressure coordination than simple pressure durations. Pressure gradients have been described to relate high propulsive pressure in the pharynx relative to low UES pressure during swallowing [27], but these have yet to be described in the pediatric population.

Table 19.1

Measures calculated from pharyngeal high-resolution manometry data

Measure	Purpose
Pharyngeal peak pressure (PP) (mmHg)	The maximal pressure (over all manometric channels or at a specific pharyngeal region) to which the pharyngeal constrictors contract during deglutition
Pharyngeal contractile integral (mmHg∗sec∗cm)	Product of pharyngeal contractile amplitude, duration, and length; a composite measure of pharyngeal contractile vigor
Pharyngeal propagation velocity (cm/s)	Describes the speed of pharyngeal peristalsis
UES resting pressure (mmHg)	Pressure in the UES during quiet rest
UES nadir pressure (mmHg)	Lowest pressure reached in the UES during relaxation; relevant in considering the ease with which a bolus may pass through the UES
UES peak pressure (mmHg)	Highest pressure reached in the UES following relaxation
UES relaxation duration (s)	Measured at nadir +20% of UES relaxation onset-nadir difference; relevant in considering the ease with which a bolus may pass through the UES
UES relaxation response time (s)	Time needed by the UES to reach its most complete relaxation; speaks to coordination of complex movements during deglutition; relevant in considering the ease with which a bolus may pass through the UES
Time between pharyngeal peak pressure and the UES nadir (s)	A marker for the coordination between pharyngeal contraction and UES function

Parameters and definitions derived from Refs. [13, 22–26]

UES upper esophageal sphincter

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