The experimental effect of myectomy of the ventral obliquae sling fibres on the lower esophageal sphincter pressure
J. Schneider, H. D. Becker (Tubingen), G. Lepsien (Göttingen)
The working method and significance of the obliquae muscle sling fibres on the fundus of the stomach for opening and closure mechanism of the lower esophageal sphincter (LES), and the consequences following after surgical treatment on esophageal motility disorders for example achalasia are still matters of controversy.
Anatomical characteristics of the terminal esophagus and fundus of the stomach
The tunica muscularis of the gastroesophageal junction shows an outer longitudinal and inner ring muscle layer. In the cardia, the inner muscle layer is divided in two parts. At the incisura cardiaca, the fibrae obliquae sling fibres start, running in dorso ventral direction from the ventral and dorsal stomach wall to the antrum. The minor curvature is free of sling fibres and shows muscle clasps. Running transversally, they represent the cardia and connect with the fibrae obliquae in an angle of 90 degrees in the submucosa layer [1].
Opening and closure mechanism of the LES
The postprandial intragastric pressure increase on the LES sphincter tonus has been recommended by Castell et al. since 1974 [2]. Works from Pettersson [3] and Marchand [4] stand, however, in opposite to this. In relation to the intra- and extraluminal changes of the stomach pressure Pettersson, Bombeck and Nyhus [3] postulated an opening and closure pressure. The increase of the intragastric pressure causes the opening of the LES and leads to a physiological reflux. The LES is closed and works as a reflux barrier when the intragastric pressure exceeds its closure strength. Particularly, the significance of the obliquae muscle fibres on opening and closure mechanism is still not investigated. The myectomy of the obliquae sling shows a normal rest pressure and a significant lower opening pressure.
Our aim was to investigate the influence of pressure and volume increase of the stomach on LES tonus before and after myectomy.
Table 1. LES resting pressure in dogs
|
Procedure |
Pressure in mmHg |
|||
|
Intact LES |
21.2 |
4.3 |
||
|
Circular myectomy |
3.7 |
1.5 |
||
|
Sling myectomy |
22.0 |
4.7 |
||
|
Total myectomy |
2.3 |
0.5 |
||
Table 2. LES opening pressure
|
Procedure |
Pressure in mmHg |
|||
|
Intact LES |
26.5 |
6.9 |
||
|
Circular myectomy |
15.2 |
4.9 |
||
|
Sling myectomy |
9.0 |
3.2 |
||
|
Total myectomy |
2.3 |
1.0 |
||
according to Samelson SL, Bombeck CT, and Nyhus LM [5]
The effects of myectomy of the ventral obliquae sling fibres on the lower esophageal sphincter pressure in dogs (own results)
Material and methods
Eight mongrel dogs of different ages, weighting between 18 and 24 kg, were inflated with air between 0.21/min and 31/min over a Kamarov throat fistula in the stomach. This was done in eleven different steps. Before operating, the flow (1 /min) the sphincter pressure (p LES), the stomach pressure (p stomach) and the maximum of volume (ml) over the time (t in sec.) till belching was measured in each animal. Afterwards a ventral myectomy (figure 1) of the fibrae obliquae sling fibres was performed, and the examination was repeated in the same way as before the operation.
Results
The eight dogs show significant increase from p LES basal x = 18.6 ± 9.86 mmHg to p LES max. x = 36.6 ± 5.77 mmHg (p < 0.001) in relation to the increase of the intragastric volume 0 to 800 ml.
The same relationship to the increase was also present from p LES, with the increase of the intragastric pressure from 7.3 ± 5 mmHg to double p max. of the stomach 14 + 5 mmHg. The duration of the inflation from the beginning until belching lasted t, x = 1.29 ± 42.8 s to t max. x = 17 ± 4.58 s.
After myectomy, the pressure increase of p LES basal 23.2 ± 4.7 mmHg to p LES max. 28 ± 1.5 mmHg was insignificant in relation to the four times as high increase of volume from 161 ± 163 ml to 110.2 ± 202 ml.
The intragastric pressure doubled from 5.7 ± 1.7 mmHg to 12.0 ± 2.8 mmHg and was not significant.
Figure 1. The fibrae obliquae sling fibers of n = 8 mongel dogs were myectomised by a 5cm long ventral incision of the stomach wall.
Synopsis
The correlation between intragastric volume increase and the LES tonus increase in humans, e.g. postprandial, was investigated earlier by McCallum [6]. Works from Pettersson and Marchand [3, 4] stand, however, in opposite to this on the basis of the LaPlace's law which states that the pressure determined increase of the stomach wall tension leads to a reduction of the LES pressure with reflux.
Our animal experiments confirmed the dependance of LES pressure of not only the intragastric volume, but also the pressure increase (figures 2, 3 and 4). In agreement with other investigators [5], we saw a decrease of LES pressure after myectomy ventral fibrae obliquae sling fibres. The weakening of the LES tonus after myectomy suggests the importance of the fibrae obliquae fibres as an important factor of the competence of the LES.
Although the transfer of this experimental data to human conditions is critical,
Figure 2. In eleven different steps, from 0.1 to 3.0 1/min, air was insufflated in the stomach until the dogs ruminated the air. We saw a good correlation between flow and pressure increase in the stomach. After myectomy, the dogs belching was noticed significantly earlier than before operation.
these results may be a model of explanation to gain a greater agreement in the question whether myotomy should be combined with an antireflux procedure. The cases of postoperative reflux esophagitis vary from 2-50% [7-12] in literature. According to that, the distal extension of the myotomy to the stomach is unclear. Ellis and co-workers [12] recommend only the short myotomy without fundoplication with an incision in the stomach of 0.5 cm. Belsey, Jara, Skinner et al. [13-17] make an incision of one cm in the wall of the stomach and combine myotomy with an antireflux procedure.
If the function of the sling fibres is to resist the increase tension of the gastric wall which overcomes in gastroesophageal reflux periods, then the lesion of the fibrae obliquae may disturb the second component of the reflux barrier by prolonged myectomy the gastric wall. This fact may explain the high rate of reflux esophagitis patients after prolonged distal myectomy, and the lower rate after the short incision in the gastric wall.
A second aspect is the prolonged transit time of the stomach in achalasia patients. Valenzuela[16], as well as our own unpublished data, have shown the lengthening of the passage time in the stomach as a possible result of a generalized motility disorder of the intrinsic vagus nerve, not only in the esophagus but also in the stomach.
Consequently, in our hospital, we have decided to continue the myectomy of Heller with the antireflux procedure of Belsey.
Figure 3. The volume increase in the stomach before and after myectomy of the fibrae obliquae till the dogs ruminate the air spontaneously. After operation the volume decreased significantly.
Figure 4. The LES pressure correlates linear with the insufflated air. After myectomy, the lower esophagus sphincter pressure decreases significantly.
References
9. Ellis FH (1988) Treatment of achalasia : a continuing controversy. Am Thorac Surg 45 : 473-475.
13. Belsey RH (1966) Functional disease of the esophagus. J. Thorac Cardiovasc Surg 52 : 164.