High-resolution impedance manometry parameters in the evaluation of esophageal function of non-obstructive dysphagia patients

Abstract

Background:

High-resolution impedance manometry (HRIM) allows evaluation of esophageal bolus retention, flow, and pressurization. We explored novel HRIM measures and assessed their temporal relationship to dysphagia symptoms for boluses of different volume and consistency in non-obstructive dysphagia (NOD) patients.

Methods:

Thirty-three NOD patients (n = 19 minor or no disorder of peristalsis (“Normal”) and n = 14 esophagogastric junction outflow obstruction (“EGJOO”)) were evaluated with HRIM. Patients were administered 5 and 10 mL liquid, semisolid, and 2 and 4 cm solid boluses and indicated bolus perception during individual swallows using a 5-point Likert scale. HRIM was analyzed to assess Chicago Classification and pressure flow metrics, esophageal impedance integral (EII) ratio, and bolus flow time (BFT).

Key Results:

Overall, bolus perception increased with increasing bolus consistency (P < 0.001), but did not differ significantly between EGJOO and Normal patients. EGJOO patients had higher IRP4, higher levels of bolus residual (ie, EII ratio and IR), and restricted esophageal emptying. The results for linking semisolid bolus perception to semisolid-derived measures revealed more biomechanically plausible and consistent patterns when compared to those derived for liquid boluses. In Normal patients, perception of boluses of heavier viscosity was related to higher bolus flow resistance during transport, whilst in EGJOO, perception was related to restriction of esophageal emptying.

Conclusion & Inferences:

These novel pressure-impedance measures may aid in the evaluation of NOD patients by revealing abnormal motor patterns, which may explain symptom generation. Future studies are needed to evaluate which of these measures are worthy of calculation and to establish protocol settings that allow for their meaningful interpretation.

1 |. INTRODUCTION

High-resolution manometry (HRM) is the primary method to evaluate esophageal motility and sphincter function in patients with non-obstructive dysphagia (NOD), that is, dysphagia in the absence of a mechanical obstruction on upper endoscopy. The incorporation of multichannel intraluminal esophageal impedance sensors onto the HRM catheter (high-resolution impedance manometry, HRIM) has enhanced the evaluation of esophageal function by allowing the assessment of the interplay between esophageal motility and bolus transit. Novel HRIM analysis paradigms have been introduced that derive esophageal pressure flow metrics that have the ability to identify subtle abnormalities of flow resistance.^1,2 Among these are the bolus flow time (BFT) and EII ratio, respectively, predicting flow across the esophagogastric junction (EGJ) or residual due to esophageal stasis as confirmed by studies using simultaneous videofluoroscopy.^3,4 These advanced HRIM metrics can be reliably calculated as supported by generally excellent inter-rater agreement.⁵ Both BFT and EII ratio have shown promising results in relation to symptom association over other manometric measures among NOD patients.^1,6 However, their application has not been studied in relation to a swallow-by-swallow bolus perception score for different bolus consistencies and volumes and analysis importantly excluded those patients with a HRM diagnosis of EGJ outflow obstruction (EGJOO). We therefore undertook a study to compare and contrast these measures and to assess their temporal relationship to dysphagia perception for boluses of different volume and consistency in a broad cohort of NOD patients.

2 |. METHODS

2.1 |. Study population

We retrospectively evaluated consecutive patients referred to the Neurogastroenterology and Motility Clinic, University Hospital Leuven, Belgium, between 17-01-2012 and 21-03-2014 with symptoms of dysphagia and clinical suspicion of ineffective bolus flow due to esophageal dysfunction. All patients underwent endoscopy and were only included in the absence of endoscopic findings of mechanical obstruction (including eosinophilic esophagitis via distal and proximal esophageal biopsies among dysphagia patients), esophagitis (more severe than grade A by the Los Angeles classification), hiatal hernia ≥3-cm, or Barrett’s metaplasia.

2.2 |. Dysphagia assessment

Subjects were asked to record their perception of the bolus during each individual swallow using a 5-point Likert scale to define the pattern of transit and intensity of perception (1 = normal, easy passage, 2 = slow passage, 3 = stepwise passage, 4 = partial blockage, and 5 = complete blockage).

2.3 |. High-resolution impedance manometry

Manometry studies were conducted using a 3.2 mm solid-state HRIM catheter incorporating 36 pressure sensors spaced 1 cm, and 16 adjoining impedance segments, each 2 cm apart (Unisensor AG; Switzerland). After an overnight fast, the assembly was placed transnasally after application of topical anesthesia (5% lignocaine spray) to the nasopharynx and positioned with sensors straddling from the hypopharynx to the stomach, with approximately three intragastric pressure sensors. All patients were studied in a 70° semi-upright position. As part of the standard manometric protocol, subjects were provided with ten liquid swallows (5 × 5 mL and 5 × 10 mL water). After liquid swallows, patients were given 10 semisolid boluses (5 × 5 mL and 5 × 10 mL applesauce) and 10 solid boluses (5 × 2 cm² and 5 × 4 cm² white bread). All bolus stock contained 1% NaCl to enhance conductivity. Solid swallows were given at >1 min intervals, and the subject was asked to chew ad libitum and then to swallow it whole. Masticating the bolus incorporates the saline into the bread bolus, improving its conductivity whilst reducing the consistency to that of a highly viscous semisolid.

2.4 |. Data analysis

All suitable liquid and semisolid swallows were analyzed by using both conventional analysis by esophageal pressure topography and integrated pressure-impedance analysis. In addition, solid swallows were analyzed for derivation of conventional parameters and for several pressure-impedance parameters (results presented separately from other bolus types due to missing data).

2.4.1 |. Pressure topography analysis

Manometry studies were analyzed using MMS (QuickView Software, version 9.3) to calculate integrated relaxation pressure (IRP4), distal contractile integral (DCI), distal latency (DL), and peristaltic breaks in the isobaric contour. An esophageal motility diagnosis was retrospectively derived by applying the Chicago Classification (CC) V3.0 criteria: A median IRP of >15 mm Hg was utilized as the upper limit of normal.

2.4.2 |. Pressure-Impedance analysis

Analysis of the pressure-impedance text data files was performed using purpose-designed analysis programs written in MATLAB (The MathWorks, Natick, MA, USA). To perform analysis, raw pressure-impedance data for all swallows were visualized over a 30-second window and exported from the recording system in text (.txt) format. The calculations used to derive pressure-impedance metrics have been previously described.^2,7 In brief, pressure-impedance recordings are displayed as pressure topography plots with embedded impedance recordings, which show bolus flow movements and relaxation and movement of the upper and lower esophageal sphincter pressure zones. On selection of specific landmarks on the pressure topography space-time plot, specific spatial and temporal regions of interest are mapped. The following pressure-impedance parameters are presented:

Measures of bolus residual:

Two measures of esophageal bolus residual were calculated based on the relationship of the nadir impedance to the impedance at the contractile peak: the esophageal impedance integral (EII) ratio and the nadir impedance-to-peak pressure impedance ratio (IR). Less effective bolus clearance and a greater degree of bolus retention are detected by greater EII ratio and higher IR.^6,8

Measures of trans-EGJ bolus flow:

The duration of bolus presence within the EGJ was determined, with the onset of bolus presence defined as the point at which the impedance dropped 90% relative to baseline impedance and the offset as the return to 50%. Using the manometry signals, the flow-permissive pressure gradient periods within the overall period of bolus presence were identified. The BFT was then calculated by the sum of these periods.^3,4 A short BFT is indicative of reduced esophageal emptying.

Other integrated pressure flow parameters:

Pressure flow parameters were measured for the distal esophagus proximal of the EGJ. The pressure at nadir impedance (PNI, mm Hg) is a validated measure of bolus distension pressure.⁹ The time interval between nadir impedance (TNIPP) and peak pressure was calculated to define the time interval of transition from a maximum distension to maximal contractile tension. Intrabolus distension pressure (IBP) slope defined the rate of pressure change during luminal closure. The pressure-flow index (PFI) was calculated as a composite measure of swallow dysfunction using the formula PFI = (PNI × IBP slope)/(TNIPP).

2.5 |. Statistical analysis

The mean value of each HRIM parameter of the five individual swallows for each bolus type and volume was utilized for each patient. Descriptive statistics for all continuous and ordinal measures are presented as median ([IQR]) unless otherwise stated. Correlations were assessed using Spearman’s rho. Groups were compared using Kruskal-Wallis or Mann-Whitney U test for continuous variables and chi-squared test for categorical variables. For multiple comparisons, post hoc tests were applied with a Bonferroni correction. Boxplots represent the interquartile (IQ) range containing the middle 50% of the values. The whiskers extend to the highest and lowest values, which are no greater than 1.5 times the IQ range. Outliers are defined as values that do not fall in the inner fences (ie, 1.5 × IQR), where asterisks mark extreme outliers (ie,>3 × IQR). P-values <0.05 were considered statistically significant. Statistical tests were performed using IBM SPSS Statistics 23 (Chicago, IL, USA).

3 |. RESULTS

Thirty-three patients were included. Patient characteristics are displayed in Table 1. Nineteen patients were classified with either a minor disorder of peristalsis or no disorder (“Normal” Group consisting of n = 5 IEM and n = 14 Normal motility). Fourteen patients (42.4%) were diagnosed with EGJ outflow obstruction (“EGJOO” Group). Patients in the EGJOO Group were older than those subjects in the Normal Group (P = 0.027). For two patients (one IEM and one EGJOO), EII ratio could not be calculated due to technical failure. Results for these patients were therefore pairwise excluded from further analysis. Data are mostly presented for liquid and semisolid boluses as two parameters (EII ratio and BFT) were not calculable for solid boluses. Where available, data on solid bolus results are provided, albeit in more limited form.

TABLE 1.

Patient characteristics stratified by CC diagnosis

	Normal	EGJOO
N	19	14
Age (median; IQR)	43.00 [36.0–57.0]	64.0 [53.3–68.3]
Female (n; %)	13 (68%)	12 (86%)
Dysphagia symptoms
Perception score	1.0 [1.0–1.2]	1.0 [1.0–1.5]
N without dysphagia (n; %)a	14 (74%)	10 (71%)
Semisolid 5 mL swallows
Perception score	1.9 [1.0–2.4]	1.4 [1.0–3.6]
N without dysphagia (n; %)a	5 (28%)	7 (50%)
Solid 2 cm swallows
Perception score	2.8 [2.3–4.0]	3.4 [2.3–4.0]
N without dysphagia (n; %)a	3 (16%)	2 (14%)

^aAverage perception score over five swallows = 1

3.1 |. Bolus perception scores

Average perception scores and number of patients without dysphagia (ie, average perception score over five swallows = 1) did not differ between the two groups. There were no significant differences in average bolus perception scores between the two groups (liquid 5 mL P = 0.801; liquid 10 mL P = 0.421; semisolid 5 mL P = 0.964; semisolid 10 mL P = 0.150; solid 2 cm P = 0.923; and solid 4 cm P = 0.788; Figure 1). Perception scores were significantly higher for solid boluses than for liquid boluses, independent of bolus volume (P < 0.01). Perception scores for semisolid 10 mL boluses were significantly higher when compared to liquid 5 mL scores (P = 0.001), but not when compared to 10 mL liquid. Similarly, 4 cm solids were significantly higher only when compared to 5 mL semisolid boluses (P = 0.001). Reported perception scores were not significantly influenced by an increase of bolus volume for the individual bolus types (Figure 1).

FIGURE 1.

Bolus perception scores for the two patient groups and different bolus types and volumes

3.2 |. HRM parameters in relation to patient group and bolus type

Per CC, patients with EGJOO had significantly higher IRP4, independent of bolus volume/consistency (Figure 2). Peristaltic break size was significantly larger for patients with EGJOO (semisolid only).

FIGURE 2.

HRM parameters, DCI, DL, IRP4, and Breaks, for liquid and viscous swallows of 5 and 10 mL. Outliers omitted from the charts for display purposes are indicated with arrows. Breaks: peristaltic break size; DCI: distal contractile integral; DL: distal latency; IRP4: integrated relaxation pressure

3.3 |. HRIM parameters in relation to patient group and bolus type

3.3.1 |. Measures of bolus residual and trans-EGJ bolus flow

Measures of bolus residual, EII ratio and IR, increased with bolus volume/consistency, and patients with EGJOO had higher residual (Figure 3A). BFT was not affected by bolus volume/consistency, but was shorter in patients with EGJOO (5 mL semisolid only). There were no differences in measures of bolus residual when patients were grouped in terms of perceived dysphagia (ie, patients grouped based on “no dysphagia” or “any dysphagia” over five consecutive swallows per bolus type and volume, Figure 3B).

FIGURE 3.

Measures of bolus residual and trans-EGJ bolus flow. EII ratio, BFT, and IR for liquid and viscous swallows of 5 and 10 mL. Outliers omitted from the charts for display purposes are indicated with arrows. BFT: bolus flow time; EII: esophageal impedance integral; IR: impedance ratio. A. Patients grouped based on CC, that is, Normal Group and EGJOO Group. B. Patients grouped based on perceived dysphagia scores, that is, no dysphagia: average perception score over five swallows = 1, dysphagia; and average perception score over five swallows >1.

3.3.2 |. Other pressure flow parameters

As a measure of swallow function, PFI increased with increasing volume/consistency and was significantly higher in patients with EGJOO (Figure 4). PNI and IBP slope also increased with increasing volume/consistency, but did not differ significantly between the EGJOO Group and Normal Group. TNIPP decreased with increasing volume/consistency, but did not differ significantly between the two patient groups.

FIGURE 4.

Pressure-impedance parameters. PNI, IBP slope, TNIPP, and PFI for liquid and viscous swallows of 5 and 10 mL. Outliers omitted from the charts for display purposes are indicated with arrows. IBP slope: intrabolus distension pressure slope; PFI: pressure flow index; PNI: pressure at nadir impedance; TNIPP: time from nadir impedance to peak pressure

3.4 |. Correlation of bolus perception with study measures

A range of different metrics were found to correlate with swallow-by-swallow perception. As bolus size did not significantly alter the intensity of bolus perception, the data for all ten swallows of both boluses volumes were used. Patterns linking liquid bolus perception to liquid-derived measures were numerous (Tables 2 and 3). However, they also appeared biomechanically inconsistent, particularly in patients in the Normal Group. In contrast, the results for linking semisolid bolus perception to semisolid-derived measures revealed more biomechanically plausible and consistent patterns (Tables 2 and 3). For example, in Normal patients, semisolid bolus perception correlated with greater bolus flow resistance during bolus transport (higher DCI, higher IBP slope, higher PFI), whilst in EGJOO patients, semisolid bolus perception correlated with restricted esophageal emptying (higher IRP4 and shorter BFT).

TABLE 2.

Spearman rank correlation of HRM parameters vs perception score

		Normal			EGJOO
Parameter	SR Corr.	Liquid	Semisolid	Solid	Liquid	Semisolid	Solid
DCI	r	0.248	0.228	−0.014	0.013	−0.087	−0.264
	Sig.	0.001	0.003	0.856	0.885	0.313	0.004
	N	189	172	162	130	135	118
DL	r	−0.120	0.007	−0.268	0.065	0.199	0.181
	Sig.	0.099	0.925	0.001	0.466	0.020	0.050
	N	189	172	162	130	135	118
CFV	r	−0.059	0.136	0.235	0.012	−0.124	−0.275
	Sig.	0.418	0.075	0.003	0.894	0.153	0.003
	N	189	172	162	130	135	118
IRP4s	r	0.081	−0.055	0.000	0.323	0.290	−0.019
	Sig.	0.271	0.476	0.996	0.000	0.001	0.835
	N	189	172	162	130	135	118
Breaks	r	−0.217	−0.136	0.062	0.166	0.207	0.361
	Sig.	0.003	0.076	0.437	0.059	0.016	0.000
	N	189	172	162	130	135	118

DCI: distal contractile integral; DL: distal latency; CFV: contractile front velocity; Breaks: peristaltic break size; IRP4s: integrated relaxation pressure; Perceived: analyzing only swallows with a perception score>1.

Bold indicates significance at P < 0.05.

TABLE 3.

Spearman rank correlation of HRIM parameters vs perception score

		Normal			EGJOO
Parameter	SR Corr.	Liquid	Semisolid	Solid	Liquid	Semisolid	Solid
EII ratio	r	−0.145	0.005	–	−0.376	−0.145
	Sig.	0.053	0.954	–	<0.001	0.104	–
	N	179	162	–	121	126
IR	r	−0.083	0.067	0.334	−0.019	0.092	−0.016
	Sig.	0.254	0.384	<0.001	0.833	0.284	0.861
	N	189	172	162	131	136	118
BPT	r	−0.075	0.130	–	0.014	0.124
	Sig.	0.303	0.090	–	0.873	0.153	–
	N	189	172	–	131	135
BFT	r	0.224	−0.033	–	−0.170	−0.257
	Sig.	0.002	0.667	–	0.052	0.003	–
	N	189	172	–	131	136
PNI	r	−0.151	0.064	0.055	0.175	−0.112	−0.308
	Sig.	0.038	0.403	0.489	0.045	0.194	0.001
	N	189	172	162	131	136	110
IBP slope	r	0.162	0.193	0.163	−0.115	−0.087	−0.220
	Sig.	0.026	0.011	0.083	0.192	0.315	0.021
	N	189	172	162	131	136	110
TNIPP	r	−0.199	0.061	−0.002	0.06	0.137	0.211
	Sig.	0.006	0.427	0.975	0.499	0.113	0.027
	N	189	172	162	131	136	110
PFI	r	0.078	0.199	0.207	−0.105	−0.148	−0.212
	Sig.	0.284	0.009	0.008	0.231	0.086	0.027
	N	189	172	162	131	136	110

BFT: bolus flow time; BPT: bolus presence time; IBP slope: intrabolus distension pressure slope; IR: impedance ratio; PFI: pressure flow index. Perceived: analyzing only swallows with a perception score>1; PNI: pressure at nadir impedance; TNIPP: time from nadir impedance to peak pressure. Bold indicates significance at P < 0.05. Results for solid boluses not available for EII ratio, BPT, and BFT.

3.5 |. Findings in relation to solid boluses

As would be expected, patients with EGJOO had significantly higher IRP4 for solid boluses when compared to patients in the Normal Group. In addition, EGJOO diagnosis showed significantly higher IR and higher PFI (P < 0.05) during swallowing of solids. All other measures were not altered in relation to diagnosis.

In the Normal Group, greater perception of solids correlated with shorter solid DL (r = −0.268, P = 0.001), higher IR (r = 0.334, P < 0.001), and higher PFI (r = 0.207, P = 0.008). In EGJOO patients, greater perception of solids correlated with larger peristaltic breaks (r = 0.361, P < 0.001) and lower DCI (r = −0.264, P = 0.004), lower PNI (r = −0.308, P = 0.001), lower IBP slope (r = −0.220, P = 0.021), and longer TNIPP (r = 0.211, P = 0.027).

4 |. DISCUSSION

In the current study, we attempted to further clarify and understand the potential clinical utility of novel pressure-impedance parameters by examining HRIM recordings obtained from a cohort of NOD patients. Importantly, for this study we included patients with Normal motility and patients with a major motility disorder, that is, a diagnosis of EGJOO. As the clinical relevance of a diagnosis of IEM remains questionable, we did not discriminate patients with IEM and Normal motility as these patients appear to have the same symptom profile and barium study findings.¹⁰ We also assessed the measurement of novel parameters in relation to a swallow-by-swallow bolus perception score for different bolus consistencies within these patient groups. Our main findings were as follows: (a) Overall, bolus perception in dysphagia patients increases with increasing bolus consistency, (b) patients with EGJOO have higher bolus residual and restricted esophageal emptying when compared with patients with Normal motility, and (c) in dysphagia patients with Normal motility, perception of heavier semisolid consistency boluses is related to higher bolus flow resistance during transport, whilst in EGJOO, perception is related to restriction of esophageal emptying.

In our cohort of dysphagia patients, there were no differences in perception scores overall between patients with Normal motility and patients with EGJOO. In line with previous studies, we found bolus perception to increase as the given bolus consistency increased from liquid to semisolid and solid. Swallowing heavier consistencies was associated with impaired esophageal bolus transport as evidenced by higher flow resistance during bolus transport (higher PFI) and bolus retention (defined by IR and EII ratio). These findings indicate that larger boluses of higher viscosity are more challenging for the system to effectively move and clear. The exact effect of differences in bolus characteristics on motor function and bolus perception is however difficult to determine. The sympathetic sensory afferent receptors that govern perception require a higher tension threshold than vagal afferents governing physiological functions,¹¹ and this threshold may differ between individuals. Despite subjects being, instructed to swallow the boluses as quickly as possible, consistency will be altered by the bolus being masticated.¹²

As expected, patients with EGJOO had significantly higher IRP4 compared to patients with Normal motility. Interestingly, EGJOO patients also showed a greater degree of bolus retention in terms of larger peristaltic break size and higher IR/EII ratio and shorter trans-EGJ BFT. In the current study, EII ratio appeared to be superior to the IR and BFT for differentiating patients with EGJOO.

Abnormalities in bolus flow, retention, and/or pressurization may account for symptom development in patients with otherwise normal manometric findings. Whilst none of the pressure-impedance parameters assessed were different in a dichotomous analysis of patients who did, or did not, report bolus perception during the study, there were some reliable correlations seen between perception of semisolid boluses and a few of the study measures. In patients with Normal motility, we found bolus perception to relate to increased esophageal resistance to bolus flow as inferred by a positive correlation with IBP slope. This observation has been previously reported^1,13,14 and suggests that in some circumstances perception may relate to a more rapidly increasing hydrodynamic pressure during luminal closure. These findings again support the ability of pressure-impedance analysis to detect subtle abnormalities of esophageal function during bolus transport.¹³ These approaches depend on automation of analysis for their objective application and may have clinical relevance by detection of abnormal functions in symptomatic patients who would otherwise be considered normal based on a conventional pressure-only analysis of esophageal HRM.

Unlike our previous study among NOD patients without a major esophageal motility disorder,⁶ a higher EII ratio and shorter BFT were not positively correlated with greater symptom perception in the study of swallow-by-swallow perception. However, in EGJOO patients, we did observe that bolus perception was related to restricted distal esophageal emptying indicated by a shorter BFT. This is the logical consequence of a major motility disorder associated with outflow obstruction and/or propulsive failure. Although we also aimed to link perception of liquids to esophageal function and emptying, results were inconsistent for liquid-derived measures. The explanation for this most likely lies in the fact that the current cohort, less frequently, reported bolus perception for liquids, whilst almost all reported perception for solids. These findings indicate that incorporation of different bolus types in the manometric protocol may improve the diagnostic yield of the study.

Patients in the EGJOO Group were older when compared to those in the Normal Group. This finding may be in keeping with EGJ outflow resistance increasing with age. It is postulated that reduced distensibility of the distal esophagus, associated with decreased bolus presence, leads to less peripheral activation of stretch receptors, involved in LES relaxation. Understanding any deterioration in sensory-motor function with age is important when one considers the number of older patients who are dysphagic and the potential impact of impaired sensory function on their dysphagia. Further studies are necessary to fully elucidate influence of age and gender on perception and swallowing mechanisms.

In addition to the retrospective design and relatively small sample size, the results of this and previous studies have not been implemented to clinical practice because the methods have required purpose-designed software. Incorporation into commercially available software packages is necessary to establish the evidence, and wider experience is required to implement these methods. To this end, we note access to pressure flow analysis is now possible via web-based application (www.http//swallowgateway.com).¹⁵

In summary, by revealing important aspects of esophageal physiology, the explored novel pressure-impedance parameters may aid in the evaluation of NOD patients by distinguishing abnormal motor flow, which may explain symptom generation. Not all patients with NOD have detectable esophageal motor abnormalities to account for their symptoms; however, some apparently demonstrate subtle dysfunctions leading to flow abnormalities that are not detectable by pressure measurement alone. On the other hand, patients with dysphagia may each have a different perception threshold and may habituate to the feeling of abnormal perception over time. Future studies are therefore needed firstly to determine which of these newly defined measures are worthy of calculation in specific dysphagia patient groups and secondly to establish the protocol settings that allow for their meaningful interpretation.

Key Points.

• Novel high-resolution impedance manometry (HRIM) esophageal pressure flow metrics have the ability to identify subtle abnormalities of flow resistance. We evaluated these measures in relation to dysphagia perception for different bolus types and consistencies in non-obstructive dysphagia (NOD) patients.

• Overall, bolus perception increased with increasing bolus consistency. Calculation of novel pressure flow metrics revealed abnormal motor patterns which were linked to symptom generation.

• Future studies are needed to evaluate which of these measures are worthy of calculation and to establish protocol settings that allow for their meaningful interpretation

Abbreviations:

BFT

bolus flow time

BPT

bolus presence time

CC

Chicago Classification

DCI

distal contractile integral

EGJ

esophagogastric junction

EGJOO

esophagogastric junction outflow obstruction

EII ratio

esophageal impedance integral ratio

HRIM

high-resolution impedance manometry

HRM

high-resolution manometry

IBP slope

intrabolus distension pressure slope

IEM

ineffective esophageal motility

IR

impedance ratio

IRP4

integrated relaxation pressure

NOD

non-obstructive dysphagia

PFI

pressure flow index

PNI

pressure at nadir impedance

TNIPP

time from nadir impedance to peak pressure