Technical aspects of clinical high-resolution manometry studies

Authors

  • A. J. Bredenoord,

    1. Department of Gastroenterology and Hepatology, Academic Medical Center, Amsterdam, The Netherlands
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  • G. S Hebbard

    1. Department of Gastroenterology and Hepatology, The Royal Melbourne Hospital, University of Melbourne, Melbourne, Victoria, Australia
    2. Department of Medicine, University of Melbourne, Melbourne, Victoria, Australia
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Address for Correspondence
Albert J. Bredenoord MD, Department of Gastroenterology and Hepatology, Academic Medical Center, Room C2-321, PO Box 22700, 1100 DE Amsterdam, The Netherlands.
Tel: +31 (0)20 566 36 32; fax: +31 (0)20 566 91 57; e-mail: a.j.bredenoord@amc.uva.nl

Abstract

Background  A number of commercial and research systems are available for making high-resolution manometry recordings.

Purpose  In this document, we review the standard equipment, patient preparation and routine protocol for high-resolution manometry. The major differences between HRM systems lie in the method of signal transduction, with solid-state catheter systems recording form intraluminal transducers and water perfusion systems recording pressures from external transducers via a perfused silicone catheter. The variations in recording systems result in different mechanical and electrical characteristics which dictate different techniques for setting up and using equipment. These issues are relevant in terms of costs and day to day management, but have little clinical significance. After the equipment is prepared for a manometric study, the esophagus is intubated transnasally with the manometric catheter and the catheter is positioned so that the UES and LES/diaphragm are visualized on the recording screen. The subject then undergoes 10 5ml water swallows in the supine position. Manometric data may be integrated with other data streams such as multichannel impedance or images from fluoroscopy to increase the power of the technique in difficult cases.

Abbreviations:
HRIM

high-resolution impedance manometry

HRM

high-resolution manometry

LES

lower esophageal sphincter

PIP

pressure inversion point

UES

upper esophageal sphincter

Introduction

In this review, we discuss the technical requirements for making high-quality measurements of esophageal pressure and the standard protocol for performing high-resolution manometry (HRM) in routine clinical practice. Analysis of measurements performed using HRM are discussed elsewhere in this supplement.

Hardware

The HRM systems consist of a manometric catheter which either contains or is connected to a series of pressure transducers, which are in turn interfaced to signal conditioning circuitry, digitization, display, and recording devices. Complete systems are available commercially from Sierra Scientific Instruments (Los Angeles, CA, USA), Sandhill Scientific (Highlands Ranch, CO, USA) and Medical Measurement Systems (Enschede, The Netherlands).

Pressures in the esophagus are converted to an electrical signal by the pressure transducer. This signal, which is initially of low voltage, is amplified and filtered, then digitized using standard circuitry interfaced to a personal computer. The digitized signal is displayed on the computer screen during the study to enable accurate positioning of the manometric catheter and allow technical problems to be resolved at the time of the recording. In parallel, the signal is recorded to a storage device, allowing offline analysis and report generation. Purpose-written software is used to display, edit and analyze the measurements, with data usually presented as a spatiotemporal Esophageal Pressure Topography plot (pressure plotted against both time and distance along the esophagus), a display method which has been shown to improve accuracy and speed of recognition of this form of data.1

Two main types of manometric catheter are used in HRM studies, solid state and water perfused. The physical and performance characteristics of the systems differ substantially with each having specific advantages and disadvantages (Table 1).

Table 1.   Characteristics of solid-state and water-perfused manometry
 Solid-state manometryWater-perfused manometry
CostsHighLow
PreparationEasyMore time consuming
Location of transducersWithin catheterExternal
Autoclave possibleNoYes
Pressure rise rateVery highMedium

In solid-state manometry, pressure transducers are mounted within the manometric catheter and are therefore at the point of measurement, with consequent benefits for dynamic response. Solid-state catheters are relatively simple to set up and use, but are more vulnerable to damage, the catheters tend to be less comfortable and more expensive, with a shorter lifespan than water-perfused catheters. The electrical characteristics of the transducer vary with temperature, and temperature compensation may therefore be required to normalize the pressures. For some solid-state systems, disposable sheaths are available to reduce the complexity of disinfection. Otherwise, catheters must be disinfected according to local protocol and the manufacturer’s instructions; however, solid-state catheters cannot be autoclaved to achieve sterilization. Reproducibility of solid-state HRM has been studied and found to be acceptable.2

In water-perfused manometry, an extruded silicone catheter containing multiple individual channels is perfused with distilled water driven by a pneumatic perfusion pump. Each channel opens to the lumen at a different point on the catheter, and pressures from that point are transmitted back along the column of water to an external transducer in the perfusion pump. These catheters are therefore cheaper, more flexible and thinner than most solid-state catheters, but are more time consuming to set up and technically demanding to use correctly. In addition, the dynamic performance of water-perfused systems is several orders of magnitude less than that of solid-state systems, which is of relevance where rapidly changing pressures must be measured (e.g., in the pharynx/upper esophageal sphincter (UES) and is dependent on the precise physical arrangement of the system and technique (e.g., perfusion rate, presence of bubbles), as well as varying with pressure. This can be measured as the ‘rise rate’ (rate at which the pressure rises when the sidehole is occluded). Rise rates of 400 mmHg, which may be difficult to achieve, are required for accurate recording of high pressure contractions and rapidly changing pressures. In contrast, the rise rates of solid-state catheters are in the region of thousands of mmHg/s, although most recording systems do not digitize and record data at a rate that makes use of these characteristics. Pressures recorded using water-perfused catheters must also be adjusted for hydrostatic pressures as well as the offset pressure required to perfuse the water through the catheter itself. Correct use of water perfusion manometry therefore requires more technical skill and training than solid- state manometry, and is subject to more technical problems and limitations. Sterilization can be achieved by autoclaving of silicone water-perfused manometric catheters. As silicone water-perfused catheters have a smaller diameter and are more flexible, in pediatric practice, water-perfused systems are used most often. However, solid-state pediatric catheters with a diameter of 2.75 mm are also available.

A variety of sensor orientations are available in HRM catheters, depending on the technology used. Water-perfused catheters have a unidirectional sensor orientation (measuring pressure at the point of the sidehole), whereas solid-state sensors may be either unidirectional or circumferential, with the circumferential sensors returning a mean pressure rather than pressures in individual directions. Although some of the structures from which pressures are measured do have a radial asymmetry (the UES and LES), the physiological and clinical significance of circumferential vs unidirectional pressure measurement has not been determined, but it seems reasonable that a circumferential system may record more reproducible data from radially asymmetrical structures such as the esophageal sphincters, whereas in the esophageal body, this issue is probably less relevant.2

To measure pressures continuously from the pharynx to the stomach without missing mechanically relevant data, the recording sites of the manometric catheter must cover approximately 30 cm for most subjects, and in some cases (e.g., a very tall subject or a dilated esophagus due to achalasia) it may not be possible to measure simultaneously across the whole region, and data may be lost from the upper sphincter (which is not generally a problem for clinical studies). In this situation, where such data is relevant, a series of swallows may need to be repeated with the catheter repositioned so that the sensors are appropriately placed to record data from the segment that was missed. All current HRM systems record over 31–35 cm, the spacing of sensors is limited to some degree by the physical nature of the sensors, currently making placement at <1 cm intervals impractical for solid-state systems. Although water-perfused systems can have more closely spaced sideholes, as the total number of perfusion channels is limited by the number of channels within the extrusion, this comes at the expense of the length of the recording area of the catheter. Although ideally, recordings would be made with as small an intersensor distance as possible, and it is uncertain what the minimal interchannel distance is to diagnose esophageal motor disorders, the Chicago Classification criteria have been developed for catheters with sensors spaced at 1 cm intervals. For example, in the Chicago classification, a weak contraction is defined as a pressure break of more than 2 cm at the 20 mmHg isobar which cannot reliably be detected with pressure sensors spaced at any more than 1 cm intervals. Moreover, detection of hiatus hernia and visualization/measurement of dynamic changes at the lower esophageal sphincter (LES) (e.g., descent of the diaphragm with inspiration, movement of the LES) cannot be accomplished with sensors spaced at more than 1 cm.3

A number of extra functions are available in some systems to record additional data to correlate the position of esophageal contents with esophageal pressure patterns. Both water-perfused and solid-state manometry catheters are available in combination with impedance monitoring segments, allowing simultaneous measurement of intra-esophageal impedance with pressures (HRIM). Alternatively, in some systems, it is possible to connect video-fluoroscopy systems to HRM data recorders so that images of bolus position can be recorded together with the pressure data.

Protocol

Equipment preparation

Before arrival of the subject, the equipment is prepared for use by setting up the recording system and performing a calibration if required.

Preparations for solid-state system recordings involve connecting a clean catheter to the recording system and checking that the sensors are functioning correctly. A two point calibration is performed in a pressure chamber or pressure tube. If a sanitary sheath is used during the measurement, the calibration is performed with the catheter in the sheath.

Preparation of water-perfused systems is more complicated than solid-state systems. Initially, the perfusion reservoir and pump are filled with water and the reservoir is pressurized to drive flow through the capillaries, with the water-channels opened to check that all channels are perfusing. As the transducers do not change their electrical characteristics significantly between studies and the same transducers are used on each occasion, a gain calibration is not required for each study, however, pressure offsets must be referenced to atmospheric pressure to account for hydrostatic and perfusion pressure offsets prior to each study. When required, a two point calibration can be performed with a perfused catheter attached and placed in a pressure chamber or tube (as for the solid-state system), or by raising the catheter by a known distance (taking advantage of the hydrostatic effects of the water column). Alternatively, the gains can be calibrated by applying two known pressures directly to the transducers without a catheter attached. The function of the catheter and recording system can be tested by lifting the catheter up 30–50 cm; pressure in all channels should increase in a similar extent. After initial setup, the catheter should be perfused with water for several minutes prior to use to ensure that the pressures are stable. Unstable pressures have a number of causes; the most common is residual bubbles in the recording system which may respond to flushing with a syringe. Other potential problems include blockage of a capillary by particles (if the water used for perfusion is not adequately filtered), leakage from a connection or cracked component, running out of water or ‘drift’ in pressures due to changes in the reservoir pressure. Staff using perfusion manometry need to be trained to recognize and deal with these problems in order for recordings to be technically adequate.

Immediately before each study, recording channels are referenced to atmospheric pressure by placing the catheter in the horizontal position at the level of the subject, and activating the zero referencing function of the software. If the measurement is to be performed in the upright or semi-supine position, the catheter is referenced in that position at the level of the subject’s esophagus.

Subject preparation

Medications and other drugs (including nicotine) that influence upper gastrointestinal motility are stopped in advance, if possible. Subjects are fasted prior to the study with a similar protocol to that used locally for upper endoscopy. In subjects with suspected achalasia, a liquid diet may be advised for one or more days before the measurement. The purpose of keeping the subject fasted is mainly to reduce the chance of vomiting and aspiration during intubation of the catheter, although the presence of food in the stomach and small intestine also has physiological effects on the LES.

The prospect of nasogastric intubation with a catheter can cause significant anxiety and careful education and instruction will improve cooperation and tolerance of the procedure. Subjects should be informed that they may experience minor discomfort in the nose and throat (which can be reduced by the use of a local anesthetic spray) as well as some possible gagging during introduction of the catheter, but will be able to breathe and speak normally when the catheter is in place. Occasionally, a vagal reaction or collapse occurs (particularly during introduction of the catheter), and staff must be prepared for this possibility. Damage to the nose, pharynx or esophagus is a rare possibility. Verbal consent should always be obtained and written informed consent may be required in some countries.

Introduction of the catheter

High-resolution manometry catheters are generally placed through the nares, although placement through the mouth is also possible. Placement through the nares is preferred as it is less uncomfortable and reduces the risk of damage to the catheter by biting. In addition, transnasal manometry allows direct measurement of the position of the LES with respect to the nares, which is required if subsequent pH-impedance monitoring is to be performed. The catheter is introduced with subject in sitting position with water available, and nasal/pharyngeal topical anesthesia if this is to be used. The catheter is lubricated and slowly introduced through the nares (it is often helpful to ask the subject whether one side of the nose is blocked so that it can be avoided), and over the floor of the nasal cavity. As the floor of the nasal cavity runs directly posteriorly, the tip of the catheter should be aimed in the direction of the ears and not upwards in the direction of the bridge of the nose. Occasionally, the tip of the catheter impacts in the posterior pharyngeal wall, which can be uncomfortable for the subject. This can be remedied by gentle manipulation/rotation or reshaping of the catheter, occasionally the other nare must be used. After 10–15 cm, the catheter will be in the hypopharynx and just above the upper esophageal sphincter. Further introduction will cause a gag reflex or coughing, which can be reduced by the subject being asked to swallow during passage of the catheter through the lower pharynx and UES. The subject is given a cup of water with a straw and is asked to take sips and swallow continuously with his/her chin down while the catheter is introduced through the sensitive area. Subjects often need to pause at this point to catch their breath, but once the catheter is through the UES, it will generally then pass easily to the stomach with minimal resistance. If the subject coughs severely during the pharyngeal phase of the insertion, passage into the larynx should be suspected and the catheter withdrawn. If significant resistance is encountered, the catheter should not be forced as this may cause damage, particularly if the tip is impacted in a diverticulum. If difficulty is encountered in the esophagus (e.g., in achalasia), it is often effective to pull the catheter back to the proximal esophagus, change the subject’s position (e.g., try lying on one side or another) and then reintroduce the catheter. Occasionally, fluoroscopy is required to pass the catheter, and rarely the catheter needs to be positioned under endoscopic visualization. Following passage across the LES, the catheter is introduced well into the stomach and pulled back to the recording position to remove any bends in the catheter caused during the introduction, thereby ensuring that distances recorded from the nares are accurate. The catheter is positioned while viewing the pressure data on the computer screen and adjusting the position of the catheter.

The catheter is positioned correctly when both the UES and LES can be recognized and when at least two pressure sensors are located in the stomach (or below the diaphragm in the case of hiatus hernia). The LES is recognized by following the pressure wave associated with swallowing, as the LES is always continuous with the termination of the swallow. In case of a very weak LES pressure, this may be recognizable only during the LES after-contraction that usually follows a swallow. In the case of very weak or absent peristalsis and a weak LES, it may not be possible to locate the LES based on pressure data. The position of the diaphragm can be determined by examining the data for the pressure inversion point (PIP). During inspiration, pressure in the thorax decreases while pressure in the abdomen increases. The point where the pressure changes with respiration meet is called the pressure inversion point; this is generally located at the level of the diaphragm.4 The PIP becomes more obvious when the subject is asked to inspire deeply, and descent of the diaphragm is also seen.

Following placement of the catheter, the subject is asked to lie down. Although the upright position is more physiological in terms of swallowing, there are differences in peristalsis when upright data are compared with supine data,5–7 and normal values for HRM and the Chicago Classification have been developed based on data recorded in the supine position. Moreover, independent of whether a solid- state or water-perfused catheter is used, when a column of water forms in the esophagus in the upright position, hydrostatic effects become relevant to esophageal emptying. This may be seen due to a relative obstruction at the gastro-esophageal junction, for example, in patients with achalasia. Nevertheless, some subjects find it difficult or impossible to tolerate lying down or to swallow in the supine position, and occasionally artifacts are seen (presumably due to compression by surrounding structures e.g., left lobe of the liver), such that it may be preferable to perform the study with the subject sitting and analyze the data in that context. Normal values have also been described for measurements in upright position.6

After the subject is placed in supine position and the catheter is correctly positioned, the subject should be allowed several minutes to accommodate to the catheter, and allow the sensors in a solid-state catheter to warm. Once the subject is comfortable, basal recordings of the LES are obtained for several minutes if possible. During the basal recording, subjects should be instructed to swallow as infrequently as possible and to breathe quietly and regularly.

Standard evaluation of esophageal motility is performed using 10 swallows of 5 cc of water in the supine position, and this should be considered to be the minimum. The value of extra swallows and changes in position has not been extensively evaluated, but may provide more information. Tap water can be used but when pressure measurement is combined with impedance monitoring, saline is used to enhance contrast on the impedance measurement. Swallows should be recorded at approximately 20–30 s intervals so that the peristaltic wave has terminated and the LES pressure has returned to baseline. If the subject swallows again before the next swallow is due, an extra period is added to avoid swallow-induced suppression of esophageal contractility.8 After the 10 swallows have been recorded, the measurement can be terminated and the catheter removed. Note that pull-through techniques are not required with HRM, as multiple sensors allow simultaneous monitoring of the entire esophagus and both sphincters. After the procedure, for solid-state systems, temperature compensation is performed, and for water-perfused systems, a short period of recording is made to ensure that channels have not drifted during the study.

Even if all preparations have been performed correctly and the protocol has been followed, measurements occasionally fail. An analysis of 2000 routine solid-state HRM studies showed that of 414 measurements (20.7%) were considered technically imperfect. Most frequently, this was because of insufficient numbers of interpretable swallows (249 measurements, 12.5% of total), the LES was not traversed (110 measurements, 5.5% of total) or there were problems with sensor or thermal compensation afterwards (28 measurements, 1.4% of total).9

Contra-indications for esophageal manometry

Although manometry is in general a very safe procedure, there are some small risks and contra-indications. Issues related to passage of the catheter are described in the previous section. In case of suspected complete or near complete obstruction, manometry is contraindicated (and not likely to be of value in any case) and a barium swallow and/or endoscopy should certainly be performed before attempting manometry. Severe coagulopathy is a relative contra-indication and may cause epistaxis, but serious bleeding is very rare. Cardiac conditions in which vagal stimulation is poorly tolerated or can cause arrhythmias are also a relative contra-indication. No data are available on the risk of bleeding in subjects with esophageal varices, but a cautious approach would be prudent (particularly in the setting of recent bleeding).

Acknowledgments

A.J. Bredenoord is supported by The Netherlands Organisation for Scientific Research (NWO).

Author Contributions

AB and GH performed the research, analyzed the data and wrote the paper.

Conflict of Interests

AJ Bredenoord received speaking fees from MMS International and AstraZeneca and received research support and educational grants from Movetis Shire, Endostim and AstraZeneca. GS Hebbard has received research support and educational grants from AstraZeneca, Janssen-Cilag and Nycomed.

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