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Chapter 19 (page 87)
Gastric Tone and the Pyloric Sphincteric Cylinder
Schulze-Delrieu (l986) pointed out that there was much uncertainty about the concept
"gastric tone". It was a term that had been widely used at the beginning of this century
and it was thought that tone determined the mechanical responsiveness of the stomach.
Radiologists elaborated on this concept by assuming that a long, angulated "fish-hook"
stomach reflected a low gastric tone; such a hypotonic stomach was associated with
delayed gastric emptying and gastric stasis. On the other hand a short, globular,
"steerhorn" stomach indicated a high gastric tone, i.e. it was hypertonic, and was
associated with rapid gastric emptying.
In order to determine gastric tone, Stadaas and Aune (l970) recorded intragastric
pressure-volume relationships in 27 patients with dyspepsia, the tension generated by the
gastric walls being measured over a range of balloon volumes. A thin-walled intragastric
plastic balloon was filled stepwise with known volumes of water; after each step the
intragastric pressure was recorded. If balloon pressures for all volumes were low,
muscular tension of the gastric wall was low, i.e. the stomach was considered to be
hypotonic. If balloon pressures were high, muscular tension of the wall was high and the
stomach was hypertonic.
In a study of gastric tone Schulze-Delrieu (l983) examined the changes in gastric
dimensions that accompanied the accommodation of volume by the stomach. He pointed
out that while distension of the stomach was seen during routine radiographic studies, it
had not been determined whether all the walls distended to the same degree, whether
distension occurred mostly in the transverse axis or in the longitudinal axis, and which
muscular structures were primarily concerned with volume accommodation. Excised
stomachs of herbivores (rabbits) and carnivores (cats) were immersed in carboxygenated
physiological solution and the shape and dimensions of the stomach, the response to
filling, the intragastric pressures and the effects of drugs were determined. It was found
that in both herbivores and carnivores the length and angulation of the lesser curvature
were little affected by filling of the stomach. During volume accommodation gastric
distension occurred mostly in the proximal stomach and along the greater curvature.
Filling the stomach increased the length of the gastric circumference. These features
could be explained on the muscular build of the stomach as a whole as determined by
Pernkopf (l929) and Torgersen (l945). Another reason for the sizeable expansion of the
greater curvature was that this curvature was concave while the lesser curvature was
convex with respect to the lumen.
Normally, according to Schulze-Delrieu (l983), intraluminal pressures rose sharply on
filling the stomach and declined thereafter. Carbachol, a known stimulant of gastric
smooth muscle, caused contraction with a shortening of the longitudinal axis, as well as
tubular contraction of the "antrum" and an increase in intragastric pressure.
Isoproterenol, a known inhibitor of gastric smooth muscle, caused a more elongated
shape, a flaccid appearance and a decrease in intragastric pressure. The findings
provided experimental proof that the degree of gastric muscle tension was reflected in the
overall configuration of the stomach. The existence of correlations between the
configuration and the state of activity or tone of the musculature was demonstrated,
thereby confirming the assumptions of early radiologists, according to Schulze-Delrieu
(l983). Consequently measurements of gastric size and configuration provide one
method of assessing gastric tone.
Another method is to measure tone by its effects on gastric volume rather than on gastric
pressure. This was done by Azpiroz and Malagelada (l985, G229) who had developed an
electronic barostat allowing the measurement of tone by recording changes in the
intragastric volume of air. The barostat consisted of an intragastric air-filled bag, the
pressure in the bag being kept constant electronically. When the stomach relaxed, air was
injected into the bag; when it contracted, air was withdrawn. Gastric tone could be
monitored from the barostat as variations in intrabag volume. Simultaneously
intraluminal pressure activity was recorded by implanted manometric catheters. Tonic
changes undetected by manometry were clearly registered by the barostat. In dogs it was
found that marked changes in gastric tone were induced by meals. Receptive relaxation
during feeding was followed by a low-tone accommodation period; this in turn was
followed by a period of sustained high tonicity.
Azpiroz and Malagelada (l985, G501) demonstrated that nutrients in the small bowel
could affect gastric tone. Fat infused into the proximal small bowel induced gastric
relaxation in canines, whereas protein had only a modest effect and carbohydrate had no
effect. In contrast, protein and carbohydrate infused into the distal small bowel markedly
reduced gastric tone, whereas fat had no effect. These authors defined gastric tone as
sustained muscular contraction of the gastric wall; variations in gastric tone probably
mediated important physiological functions such as accommodation to a meal and
emptying of liquids.
Schulze-Delrieu (l986) stated that physiologists working with isolated strips of gastric
musculature abhorred the term gastric tone, as it was imprecise and reflected a judgment
on gastric muscle tension as gained from purely visual or radiographic inspection.
However, more precise measurements of gastric tone had been made with the use of
gastric balloons. In his view gastric tone referred to the tension generated by the gastric
walls. It affected the ability of the stomach to accommodate volume and to generate the
driving force for gastric emptying. Experimental studies (Schulze-Delrieu l983) provided
proof that the degree of gastric muscle tension development was reflected in the overall
configuration of the stomach. If it was stimulated, the stomach was short and globular; if
it was inhibited, the stomach was long and flaccid. The longitudinal musculature of the
proximal greater curvature had a pivotal role in the overall control of gastric tone.
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