Barry McMahon, Department of Gastroenterology, Centre for Visceral Biomechanics and Pain, Aalborg Hospital, Hobrovej 18-22, 9000 Aalborg, Denmark. Tel: +45 99322483; fax: +45 99322503 e-mail: email@example.com
Knowledge of the competence of the oesophago-gastric junction (OGJ) is fundamental to the understanding of gastro-oesophageal reflux disease (GORD), a disorder with a high incidence among the general population. A catheter with a bag 9.5 cms long mounted towards the distal end was swallowed by three volunteers. Using manometry readings and the point of respiratory inversion as a guide the probe was placed in the OGJ. The bag was distended with saline at a fixed rate volume before and after the administration of butylscopolamine to block cholinergic-mediated contractile smooth muscle activity. Using impedance planimetry three cross-sectional areas (CSA) measurements were made between three pairs of electrodes with 4 mm between each electrode on the catheter placed inside the ballon. Using the law of Laplace, CSA and pressure data could be calculated to give wall tension. Tension rose in all volunteers as the radius increased and it was higher towards the proximal end of the OGJ indicating that this measurement can be used to show the distensibility of the OGJ at different degrees of opening. This technique could be useful in identifying changes in the competence of the lower oesophageal sphincter in some patients with GORD.
The mechanism at the distal end of the oesophagus, referred to as the oesophago-gastric junction (OGJ), is the principal barrier protecting the oesophagus from gastric juice. There is a high incidence of gastro-oesophageal reflux disease (GORD) among the general population, and knowledge of the competence of the OGJ is fundamental for the understanding of GORD.1
In biomechanical terms the overall ability of the OGJ to distend is related to a myriad of factors including muscle tone, passive viscoelasticity, mechanoreceptor-mediated reflexes, perception and bolus transport.2 However, to identify individual effects of these factors would be unwieldy and therefore not easily assimilated into current clinical practice.
If pressure and radius can be measured simultaneously in the lower oesophageal sphincter (LOS), the circumferential tension in the wall can be estimated. This idea was investigated by Biancani et al. almost 30 years ago,3 but only recently have biomechanical measurements in the OGJ been revisited.4 The objective of the current work was to measure pressure and cross-sectional area (CSA) at three levels in the LOS using a new multi-electrode impedance planimetry (IP) bag distension technique. It is then possible with some geometric assumptions to calculate the circumferential wall tension in the OGJ at multiple levels. This technical note presents such a technique that can be further modified for obtaining a fine-resolution 3D-profile of the OGJ in a subject with GORD.
For this study a new multi-lumen probe design with a polyvinyl catheter tube 1.5 m in length and 4.5 mm in diameter was used. A polyurethane IP bag mounted towards the distal end was used to distend the OGJ. The 9.5 cm long bag was inflated to 2.5 cm in diameter without contributing to the resistance to inflation. Figure 1A shows the probe in situ. The IP bag was filled with a 0.009% saline solution from a channel through six infusion holes spread across the length of the catheter where the bag was placed. Three pressure measurements were made with a low compliance perfused system connected to external transducers. Inside the bag a constant electric current across the excitation electrodes (E) causes the impedance to change at the sensing electrode pairs P, M and D, in proportion to the CSA of the bag at these points.2
The probe and pressure transducers were connected to a physiological measurement system (GMC Aps, Hornslet, Denmark) capable of plotting CSAs and pressures in real time, and all data were stored on a computer for off-line tension analysis based on LaPlace's law. The system was set up and calibrated as per established procedures for CSA and pressure measurement.2
Three volunteer pilot studies were carried out using this probe to a protocol approved by the Local Ethics Committee. The volunteers fasted for 12 h prior to the study. They were included on the basis that they were healthy, had no history of reflux disease, or treatment for any associated conditions.
The subjects were supine to minimize the effect of gravity with their head tilted by 30°. The deflated bag was swallowed by the volunteers and pushed all the way into the stomach. Then it was slowly retracted until the point of respiratory inversion was identified by the proximal pressure hole indicating the position of the OGJ. The probe was then further retracted to place the sensing electrodes exactly in the centre of the OGJ. This position was confirmed by the proximal pressure hole detecting peristaltic action in the oesophagus during swallowing, while the distal pressure hole only experienced slow fluctuations confirming its position inside the stomach. This technique was validated by separate pilot studies where, after probe placement, real-time magnetic resonance images of the probe in situ and during distensions were acquired. This confirmed that the probe remained in the OGJ. Bench tests were also performed with PVC tubes to confirm accuracy of measuring multiple CSAs at small and large sizes, especially when different CSAs are being measured concurrently.
The bag was distended using a saline solution at a fixed flow rate of 40 mL min−1 using a 60-mL syringe driver pump (Harvard Apparatus, Holliston, Ma., USA). Once started the criteria for stopping the saline infusion was when the bag was almost fully filled at 40 mL, or before if the volunteer experienced pain. The long bag ensured that it would not dislodge easily from the high-pressure zone.
After two preconditioning distensions two further distensions of 40 mL min−1 were recorded.2 Swallowing was prohibited and if any occurred then the distension was repeated. A further two 40 mL min−1 distensions were performed 2 min after the administration of 20 mg of butylscopolamine to block cholinergic-mediated contractile smooth muscle activity.5
Figure 1B shows the change in the bag pressure during a volume infused distension before (N) and during (B) the administration of butylscopolamine for one of the volunteers. In Fig. 1C it can be seen that the distal CSA distends first followed by the middle CSA and then the proximal CSA. Figure 1D shows second-order polynomial curve fits for calculated scatter data of radius vs tension collected from two distensions for proximal, middle and distal CSAs for one of the volunteers. This pattern was observed for all three volunteers.
Discussion and perspectives
This multi-electrode technique can use CSA and pressure data to calculate the distensibility of the OGJ at different degrees of opening. In part, it confirms the work of Pandolfino et al.6 who also used CSA and pressure but with a different technique and to make a different biomechanical measure, i.e. flow. The technique described in this work has never been demonstrated before and shows that biomechanical data on the OGJ function can be gathered by a direct method. It confirms the work of Biancani et al.3 demonstrating that at different amounts of OGJ opening the pressure will change. This method is superior to oesophageal manometry where the dynamic relationship between sphincter opening and pressure is not considered in the characterization of LOS function.
The results suggest that it is possible to distinguish between a toned and a relaxed OGJ by placing a fixed rate volume infused bag in the junction and monitoring the pressure and CSA in the bag. This confirms that the effect of the OGJ on a distending bag is to cause a change in the bag pressure with increased wall tension towards the proximal end of the OGJ.
The filling pattern of the bag observed from the three CSA plots suggests that it fills from the distal end as the infusion holes at this end appear to offer the path of least radial resistance suggesting that the junction is less compliant distally. This is probably due to a conical shape in the OGJ narrowing towards the proximal end. Gravity is likely not a confounding factor because of the supine position. There was an increase in wall tension in the OGJ with increase in radius during the distensions. The proximal wall tension rose higher at a lower radius, suggesting that the OGJ becomes less distensible towards the upper end. These findings are consistent with Cray et al.7 who confirmed that the OGJ constitutes an overlapping of the LOS and the crural diaphragm towards the proximal end, but only the crural diaphragm appears towards the distal end. More studies and data are needed to confirm this.
Changes in the pressure profile of volunteers after the administration of butylscopolamine suggest that with this technique it may be possible to identify changes in the competence of the LOS in some patients with GORD. It should however be noted that butylscopolamine will eliminate the cholinergic component of LOS tone but not the myogenic component. This technique is no more difficult to perform than manometry. However, use of a probe with a smaller diameter would provide valuable data on tension during the more critical part of the intonation of the sphincter where greater differences between competent and incompetent sphincters are found. An increased number of detection electrodes will also give better axial resolution and help with probe movements during the test. This should be considered in future experiments.