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Keywords:

  • common cavity;
  • impedance;
  • manometry;
  • pH monitoring;
  • reflux

Abstract

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. References

Abstract  The manometric common cavity phenomenon has been used as indicator of gastro-oesophageal reflux of liquid or gaseous substances. Using combined pH and impedance recording as reference standard the value of a common cavity as indicator of gastro-oesophageal reflux was tested. Ten healthy male subjects underwent combined stationary pressure, pH and impedance recording for 4.5 h. After 1.15 h of recording, a reflux-eliciting meal was consumed. The chi-squared and Kolmogorov–Smirnov tests were used for the statistical analysis. A common cavity was found in 95 (43%) of the 223 reflux events detected by impedance, while seven common cavities were unrelated to a reflux episode. In 54% of the reflux events detected by impedance without a common cavity, a possible common cavity was obscured by either contractile activity or artefacts of various origin. The types of reflux associated with a common cavity (liquid 60%, mixed 31%, gas 9%) and without a common cavity (liquid 59%, mixed 29%, gas 12%) did not differ, or did the acidity of the reflux episodes (with common cavity: acid 67%; without common cavity: acid 58%). The common cavity is a specific but not a sensitive marker of gastro-oesophageal reflux. Furthermore, common cavities are not specific for a particular type of reflux.


Introduction

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. References

During relaxation of the lower oesophageal sphincter (LOS) a connection is formed between the oesophagus in the thoracic cavity and the stomach in the abdominal cavity.1 This phenomenon can be observed manometrically as a simultaneous intra-oesophageal pressure rise to gastric pressure level and this is referred to as the common cavity phenomenon.1–3 The first description of this phenomenon was reported by McNally et al. in 1964.3 They observed that when air escaped from an inflated stomach, equalization of gastric and oesophageal pressures occurred. In many subsequent studies the common cavity phenomenon has been used to detect gaseous reflux or belching.3–11 However, others observed that reflux of liquid material was also able to create a common cavity, as most acidic reflux episodes were found to be associated with this phenomenon.1,2,12–15 As a consequence, common cavities associated with a fall in oesophageal pH were interpreted as acidic liquid reflux and common cavities without pH change as gaseous reflux.11,12,15 Recently, the use of intraluminal impedance monitoring has made clear that a low pH does not always imply the presence of liquid reflux while non-acid reflux can also contain liquids. As impedance monitoring can detect both gas and fluid transport in oral and aboral direction it is, in combination with pH recording, the most optimal method for assessing the type and acidity of reflux events.15 Therefore, the aim of this study was to test the value of reflux detection by means of common cavity analysis, using combined impedance and pH recording as reference.

Methods

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. References

Patients

In this study, 10 healthy male volunteers [age 28 ± 3 years and body mass index (BMI) mean 22 ± 0.7 kg m−2] underwent combined stationary manometry, pH and impedance recording for 4.5 h. All volunteers were free of gastrointestinal symptoms and did not take any medication. Two days before recording all volunteers refrained from smoking and alcohol use. Informed written consent was obtained before the start of the study and the protocol was approved by the Medical Ethics Committee of the University Medical Center, Utrecht.

Study protocol

After an overnight fast, a manometry catheter (described below) was inserted through the nose. After positioning of the manometry catheter, the impedance and the pH catheter were transnasally introduced and positioned according to the manometric pressure profile (see below). All subjects were in an upright position during the recording period and were asked to minimize movements. After 1 h and 15 min of continuous recording, a reflux-eliciting meal was consumed consisting of a hamburger (McDonald's Quarter Pounder), 20 g of fresh onions, 44 g of chips and 475 mL of orange juice (in total 967 kcal). The meal had to be finished within 15 min. A postprandial recording period of 3 h completed the protocol.

Manometry and pH monitoring

For manometry a water-perfused 10-channel silicone rubber assembly with inner diameter of 0.4 mm and outer diameter of 4 mm with a 6 cm long reversed-perfused sleeve sensor (DentSleeve International Ltd, Mississauga, ON, Canada) was used. The manometric catheter was positioned such that the sleeve sensor straddled the LOS. Four pharyngeal side-holes (at 24, 26, 28 and 30 cm proximal to the upper border of the sleeve), three oesophageal body side-holes (at 4, 9 and 14 cm proximal to the upper border of the sleeve) and a gastric side-hole (2 cm distal from the sleeve) were used to record pressures. The sleeve sensor, gastric and oesophageal side-holes were perfused at a rate of 0.2 mL min−1 with degassed water, using hydraulic flow restrictors (DentSleeve International Ltd). The pharyngeal side-holes were perfused with air at a rate of 0.8 mL min−1. The side-hole that registered the pharyngeal contraction best was selected while the other pharyngeal side-holes were not perfused in order to prevent mechanically stimulated transient LOS relaxations (TLOSRs).16 Pressures were recorded with external pressure transducers (Abbott, Sligo, Ireland). Intraluminal pH monitoring was performed with a glass pH catheter (Ingold AG, Urdorf, Switzerland) that was positioned 5 cm above the manometrically defined upper border of the LOS. The pH data were stored together with the manometric data in digital format in two 12-channel data loggers (MMS, Enschede, The Netherlands), using a sample frequency of 8 Hz. At the end of the study all data were transferred to the hard disc of the computer.

Impedance monitoring

For impedance monitoring a 7-channel impedance catheter (outer diameter 2.3 mm) was used (Aachen University of Technology, FEMU, Aachen, Germany). The seven recording segments formed by pairs of ring electrodes at 2-cm intervals were located at 0–2, 2–4, 4–6, 8–10, 10–12, 14–16 and 17–19 cm above the upper border of the manometrically located LOS. Impedance signals were stored in a digital system (Aachen University of Technology) using a sampling frequency of 50 Hz.17

Data analysis

The period of meal consumption was excluded from the analysis. Comparisons were made between impedance- and pH-detected reflux episodes coinciding with a manometric common cavity and those without a manometric common cavity. In the impedance signals, reflux episodes were identified and classified as either liquid, mixed or gaseous reflux based on previously described criteria.15 Furthermore, using the pH tracings, the reflux events were classified as either acidic (pH <4) or weakly acidic (pH 4–7), weakly alkaline (pH >7) or superimposed reflux.15

A common cavity was defined as a rise in oesophageal body pressure to gastric pressure that occurred within 1 s and that was maintained for at least 0.5 s in at least two of the three oesophageal body pressure tracings (see Fig. 1).11,13 To determine why some common cavities are seen only in distal and others only in proximal pressure tracings, the proximal and distal visible common cavities were compared. A proximal common cavity was defined as a pressure rise that was seen in all oesophageal pressure channels or in the two most proximal oesophageal channels. A distal common cavity was defined as one in which the pressure rise was visible in the distal two pressure channels.

image

Figure 1.  An example of a common cavity phenomenon characterized by a sudden and sustained rise in oesophageal pressure to gastric pressure in all three oesophageal pressure channels. In this example the common cavity phenomenon is associated with a transient lower oesophageal sphincter relaxation and gas reflux, as indicated by a sudden rise in impedance that propagates to the most proximal impedance channel.

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Artefacts caused by body movement, coughing or straining were defined as a simultaneous pressure increase or decrease in all tracings.

The liquid volume clearance time was defined as the time interval between a drop of ≥50% of baseline impedance and the return to a value above this point. Acidic clearance time was defined as the time when the pH was below 4 during a reflux episode.

The duration of a common cavity was measured from maximum distal oesophageal pressure rise until drop of pressure or until a secondary peristaltic wave.

Statistics

The chi-squared and Kolmogorov–Smirnov tests were used to determine statistical differences between variables. Differences were considered statistically significant when P < 0.05. The data are presented as median (interquartile range).

Results

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. References

All 10 healthy volunteers completed the protocol and a total of 223 reflux episodes were detected with combined impedance-pH monitoring. In the manometry recordings 102 common cavity events were found. Ninety-five of the 223 reflux episodes identified on impedance-pH monitoring (43%) were accompanied by a common cavity. In 54% of the 128 reflux events without a common cavity the events were obscured by the co-occurrence of swallow-induced peristalsis, non-swallow-induced peristalsis or artefacts. The 46% remaining reflux events without a common cavity the pressure signal was well interpretable but these events did not meet the criteria for a common cavity. The seven common cavity events that were not detected by combined impedance-pH monitoring were not analysed further.

Sixty-four percentage (61 of 95) of all reflux episodes with a common cavity was associated with a pH drop below 4. Three of the nine gas reflux episodes identified by a common cavity coincided with a pH drop below 4 and 17 of the 57 liquid reflux events were weakly acidic. The type and acidity of the reflux episodes detected by a common cavity did not differ from those detected by impedance monitoring (see Fig. 2A). Most common cavity reflux episodes coincided with acidic liquid reflux (P < 0.01, see Fig. 2B). Weakly alkaline and superimposed reflux events were rare [both 1.8% (four of 223)] and occurred during both reflux with and without a common cavity phenomenon.

image

Figure 2.  Distribution of subtypes of reflux episodes, classified according to physical [(A) liquid, gas and mixed; (B) liquid containing] and chemical [acid (A), weakly acidic (WA)] characteristics of the refluxate, with and without associated common cavity.

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The proximal extent of gaseous and liquid reflux events with and without a common cavity was similar as were the nadir pH, acid and volume clearance times (see Table 1).

Table 1.   Characteristics of reflux events with and without a manometric common cavity
 Without common cavityWith common cavity
nMedian (25–75th)nMedian (25–75th)
  1. The number (n) for gas and liquid events listed in this table include the separated gas and liquid components of mixed reflux events.

Gas extent (cm)5218 (18–18)3818 (18–15)
Liquid extent (cm)1139 (5–15)8613 (9–15)
Volume clearance (s)11315 (11–22)8616 (13–22.3)
pH begin1136.0 (5.4–6.7)866.2 (5.8–6.6)
pH nadir682.7 (1.9–3.2)692.7 (2.0–3.7)
Acid clearance (s)6513 (6–124)5916 (6–56)

Most (85% = 81 of 95) common cavities were visible in the proximal oesophageal pressure tracing. The proximal extent of liquid and gaseous reflux events was not significantly different for proximal or distal common cavities (see Fig. 3). Comparable acid [proximal 16 (7–49), distal 29 (6–76)] and volume clearance time [proximal 16.0 (12.0–22.0), distal 18.5 (14.5–24.8)] were found for proximal and distal common cavities. The median duration of a common cavity was 6 s (4–8). The duration of proximal [6.0 (4.0–8.0)] and distal common cavities [6.0 (4.0–9.5)] were similar.

image

Figure 3.  The proximal extent of gas (grey dots) and liquid (black dots) reflux events did not differ between proximal and distal common cavities. The horizontal lines represent the group median.

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Discussion

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. References

Since the 1960s, the manometric common cavity phenomenon has been regarded as indicative of the presence of gastro-oesophageal reflux, but its true value as a reflux indicator could not be assessed, due to the absence of a gold standard. Nowadays combined intraluminal impedance and pH recording is considered the most optimal way to study reflux and this technique was therefore used as reference standard to determine the value of the manometric common cavity phenomenon as a gastro-oesophageal reflux indicator.15

We found that common cavities represented 43% of all reflux episodes detected with the combination impedance and pH, indicating a low sensitivity. Nevertheless, a high specificity was found as most common cavity phenomena (93%) coincided with reflux events observed by combined impedance-pH recordings. Half of the reflux episodes without a common cavity phenomenon did not meet the criteria. Interpretation of the manometric tracings of the other half of the reflux events without a common cavity was complicated by pressure increasing events (swallow-induced peristalsis, secondary peristalsis, spontaneous contractions or artefacts). This finding underlines the advantage of reflux detection by impedance monitoring. Impedance tracings are less affected by events that increase intra-oesophageal pressure.

Previous studies have confirmed the fact that manometry performs less well than impedance and pH monitoring.18,19 However, in these studies only 23–31% of the reflux events detected with pH and impedance were missed with the common cavity phenomenon compared with the 57% found in this study. The discordance with our study could be due to the fact that in both studies the volunteers were in recumbent position during the recording. In a recumbent position, gravity prolongs the presence of refluxate in the oesophagus. Manometrically, this results in a higher proportion of reflux episodes coinciding with a common cavity pressure pattern.20 Furthermore, the study by Shay and Richter18 included gastro-oesophageal reflux disease (GORD) patients who presumably could have greater refluxate volumes than healthy volunteers, facilitating the occurrence of a common cavity.18,20,21

As it is not possible to detect gaseous reflux with pH monitoring, common cavities have been used as indicator for this type of reflux.3–11 We, however, found in our study that common cavities can be caused by pure liquid, pure gaseous and mixed gas–liquid reflux, and thus do not exclusively result from gaseous reflux. Most common cavities were associated with acidic liquid reflux, which is the most common reflux type in healthy volunteers.22 It seems that the reflux episodes visible as a common cavity reflect all reflux types that can be found with impedance monitoring. Furthermore, our findings disprove the assumption that a common cavity associated with a pH drop represents liquid reflux. Thirty-three percentage of the gaseous reflux events presenting as a common cavity had a pH below 4 while 30% of the liquid reflux episodes with a common cavity phenomenon was weakly acidic. Gaseous reflux without identifiable liquid component but with a pH drop below 4 has been described before as ‘acid vapour’.21

For the detection of reflux both impedance monitoring and manometry are depended on the volume of the refluxate, in contrast to pH recording. It has been shown that impedance can detect volumes as small as 1 mL, while probably more volume is required to raise the intra-oesophageal pressure to intra-gastric level.23 The exact quantity needed is unknown and whether or not this reflux volume leads to a distension of the oesophagus remains to be investigated.19,24,25 We, however, did not find any difference between the volume clearance time for the episodes with and without a common cavity, or did the volume clearance time differ between reflux episodes with proximal or distal common cavities, indirectly suggesting that the volume of reflux episodes with and without common cavities may have been similar.

Furthermore, no differences were found between the proximal extent of liquid or gaseous reflux between reflux events with and without a common cavity which suggest that these reflux characteristics are of no influence on the presence of a common cavity phenomenon. In addition, the visibility of a common cavity phenomenon was not depended on the proximal extent of the refluxate or on the duration of a common cavity.

In this study, a manometric common cavity phenomenon was considered to represent equalization of gastric and oesophageal pressure during opening of the LOS and to be associated with flux of gas, liquid or both from the stomach to the oesophagus.2 However, in a recent pH impedance and ultrasound combined study it was suggested that a common cavity wave was not due to movement of gastric contents into oesophagus but the effect of oesophageal longitudinal muscle contractions.19 These conclusions were based on the observation that the time of onset of reflux as detected by impedance was not consistently associated with a common cavity pressure wave. We believe, however, that the authors may have used a too short time interval (0.1 s) to be able to link a common cavity pressure rise with reflux entry in the oesophagus. The potential error that results from the use of three separate catheters for recording three different physical entities (pH, pressure and impedance) with their different velocities, presumably sampled at different frequencies (unmentioned for both pH and manometry) may have been bigger than the selected time interval. The authors’ conclusion that a simultaneous manometric common cavity pressure rise is unlikely to be due to retrograde travelling gastro-oesophageal reflux as seen with impedance may therefore be incorrect.

In conclusion, the manometric common cavity phenomenon represents a specific but insensitive indicator of gastro-oesophageal reflux. Common cavities frequently coincide with acid liquid reflux events and they are thus not exclusively representative for gaseous reflux.

References

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. References
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