Do motorized pull-through techniques give further information? What are the normal values for these techniques?
M. Costantini (Padova), R.M. Bremner, S.F. Hoeft,
P.F. Crookes, T.R. DeMeester (Los Angeles)
The lower esophageal sphincter (LES) represents the most important factor in gastroesophageal junction competence [1, 2]. It has been demonstrated that about 60% of patients affected by gastroesophageal reflux disease (GERD), as detected by 24-hour pH monitoring of the distal esophagus, have a defective LES [3]. Such patients frequently have symptom relapses after medical treatment; they become drug-dependent and are only cured by surgery [4]. Careful evaluation of the LES is therefore mandatory in patients with suspected GERD. It is usually performed, at manometry, using the station pull-through (SPT) [5] or the rapid pull-through (RPT) technique [6, 7]. Both techniques have certain drawbacks, however: RPT has proved less reliable than SPT [8, 9] and does not allow for the identification of the respiratory inversion point (RIP) and the abdominal segment of the LES. On the other hand, SPT is time-consuming and requires the patient's valid cooperation. A new method for assessing the manometric characteristics of the LES, called the "slow motorized pull-through" (sMPT), has recently been introduced [10]. It combines the advantages of both SPT and RPT and, since the technique is operator-independent, it is ideal for computer analysis.
Methods
The test is performed with a low-compliance infused system, consisting of a standard multilumen catheter, with 4 side holes located at the same level and arranged at 90° angles. Additional side holes, spaced 5 cm apart, are used for the study of esophageal peristalsis. Pressure signals are detected by external transducers located at the mid-axillary level, recorded on paper at a 2.5 mm/sec paper speed, and recorded on computer at a rate of
60 Hz for further analysis.
After overnight fasting, the catheter is passed through an anesthetized nostril until all the side holes are located in the stomach, and the gastric pressure pattern is confirmed. A belt pneumograph around the chest records the respiratory excursions. The catheter is then withdrawn through the cardia at a constant low speed (1 mm/sec), using a motorized puller device. The subject is encouraged to breathe normally, but to refrain from swallowing. In case of the patient inadvertently swallowing, the sMPT is easily repeated until a "clean" trace is obtained (Figure 1).
The manometric test is then completed in the usual way, evaluating the LES relaxation and esophageal body motility response to dry and/or wet swallows, as well as the characteristics and function of the upper esophageal sphincter.
Manometric measurements are performed as described previously for the traditional SPT technique [3]: the beginning of the sphincter is considered as the point at which the pressure line rises constantly 2 mmHg above the gastric baseline. The RIP is identified as the first point at which pressure excursions, which are initially in phase with respiratory excursions, change sign. The end of the sphincter is considered as where the pressure trace reaches the esophageal end-expiratory baseline. The resting pressure of the LES is measured at the RIP, in mid-expiration, in relation to gastric baseline. The overall length of the LES is measured in cm from the beginning to the end of the sphincter, and the abdominal length is measured from the beginning to the RIP. The mean of the
4 measurements obtained with the sMPT are considered.
Figure 1. Manometric traces of the LES obtained with the sMPT in a healthy volunteer, using four side holes located at the same level and oriented at 90° angles. The RIP is easily identified and the abdominal length of the sphincter can be evaluated. The asymmetry of the sphincter is clearly evident: the sphincter is longer in the lower trace and the pressure is higher in the upper trace. (From [18].)
Results
In order to validate the technique, we compared the sMPT with the traditional SPT in
20 healthy volunteers (11 males and 9 females; median age 32 years, range 23-40) and in 100 consecutive patients with a variety of foregut diseases and undergoing esophageal function tests (46 males and 54 females; median age 47 years, range 19-83) [10].
A good correlation was found between the values obtained with the sMPT and the SPT for the LES pressure, overall length and abdominal length in the 120 subjects (r = 0.91,
r = 0.77 and r = 0.71, respectively, Spearman's rank correlation test). The results were also comparable when the healthy volunteers and patients were considered separately. However, though the mean values of the LES resting pressure obtained with the two methods were comparable, the sMPT gave significantly higher values for overall length and abdominal length than the SPT. This meant that new "normal" ranges were needed, and we calculated these as the 5th and 95th percentiles of the values obtained in the 20 healthy volunteers (Table I).
In order to assess the reproducibility of the sMPT, the technique was performed three times, at twenty-minute intervals, in 24 subjects (8 volunteers and 16 patients). The pressure, overall and abdominal length values obtained with the 3 repeated pull-throughs showed no differences (Friedman test).
Finally, 29 of the patients evaluated were shown, on esophageal pH monitoring, to have gastroesophageal reflux disease (GERD). At our institution, we define a manometrically defective sphincter as one revealing values for resting pressure, overall length or abdominal length below the normal range [3]. Using these criteria, the sMPT identified a defective sphincter in a slightly higher proportion of cases than traditional SPT (59% vs 48%).
Comment
First identified by Fike et al. in 1959 [11], the LES is widely considered the most important factor in determining the competence of the esophagogastric junction and preventing gastroesophageal reflux [1, 2]. Two methods are currently used for the manometric evaluation of the LES. The station pull-through (SPT) method [5], which consists in withdrawing the catheter across the cardia in steps of 1.0 cm, while the subject is breathing normally. At each step, pressures are recorded for at least two respiratory cycles, or until a stable trace is obtained. In order to overcome the drawbacks of the method, which is time-consuming and requires the patient's valid cooperation, a rapid pull-through (RPT) method was developed [6, 7], which consists in the high-speed (motorized or hand-controlled) withdrawal of the catheter across the cardia (at 0.5-1 cm/sec), while subjects hold their breath. A critical assessment of this method has shown its poor reproducibility and scarce correlation with SPT, however [8, 9]. In addition, and most important, this method does not allow for the identification of the respiratory inversion point (RIP), consequently making it impossible to separately evaluate the intra-abdominal segment of the LES, which has proved important in the overall competence of the sphincter [3]. Therefore, although some laboratories still prefer the RPT for its simplicity and the easy interpretation of its traces, the majority of authors prefer to evaluate the LES by means of the SPT.
The slow motorized pull-through described here is something in between the SPT and the RPT. It combines the advantages of both techniques, without their drawbacks. It is quick, and therefore well tolerated by the patient, and easy, since it is performed by the machine. This means that the measurement can be repeated in the event of the patient swallowing, or to obtain a larger number of measurements for averaging, or to evaluate variations in LES characteristics over time (e.g. following drug administration) as an alternative to using a sleeve device. It gives good-quality tracings (Figure 1), that are easy to analyze. Identification of the RIP inside the curve is also easy, facilitating the evaluation of the length of the segment of sphincter below this point, i.e. the segment of sphincter exposed to positive intra-abdominal pressure. It also demonstrates a low intra-individual variability over time.
Moreover, sphincter length measurements can be made with the sMPT to the nearest millimeter, whereas the SPT measurements only have a resolution of 0.5-1 cm, i.e. the distance between two steps. The sMPT consequently provides a more precise result, which may explain the difference we found in the lengths measured by the two methods in the same subject, making it necessary to calculate new normal ranges (Table I).
Another important advantage of the sMPT technique is that it is operator-independent, allowing for a far better standardization of the procedure. With currently-available computer systems for pressure data acquisition and analysis, new parameters can be calculated for manometric LES competence, such as the mean pressure along the curve and the area under the curve [12]. In addition, because of its well-known radial asymmetry [13], the LES is usually evaluated with radially-arranged side holes, and the pressure values obtained are averaged to compensate for this asymmetry. Computer-aided three-dimensional representations of the sphincter, with the calculation of its vector volume using the pressure values as radii of this solid, have recently been introduced [14-16]. However, due to difficulties in designing reliable algorithms for evaluating the SPT traces, the RPT had to be used for the sake of simplicity [14, 15], though this meant giving the figure the drawbacks typical of the RPT technique (variability and the inability to locate the RIP). When the SPT was used, a semi-manual analysis was required [16]. The sMPT can overcome these problems: the absolute standardization of the method ensures that all the data can be stored and analyzed with no intervention from the operator, and the vector volume can easily be calculated by computer using all the acquired data. Though extensive studies are needed to evaluate the clinical usefulness of these new parameters (mean pressure, area under curve and vector volume), they seem very promising [12, 17].
In conclusion, the sMPT is a reliable method for evaluating the LES: it couples the advantages of the well-established SPT with a rapid execution and high-quality traces. The full standardization of the procedure ensures easy computer acquisition and analysis, for a modern, objective manometric evaluation of LES characteristics.
References