These esophageal contractions parallel with the gastric hunger contractions are apparently not identical with the esophageal contractions reported by Cannon and Washburn. These observers noted that the esophageal contractions were more prolonged than the gastric contractions of the same man during other hunger periods. The contractions noted by us are usually briefer than the parallel stomach contractions. Washburn was able to associate the esophageal contractions with the sensation of hunger pangs. None of us are able to do that. In the first place the esophageal contractions that occur spontaneously during quiescence of the empty stomach contractions that may be identical in rate and strength with those parallel with the gastric hunger contractions are either not felt at all, or else felt as a disagreeable fulness in the throat, something stuck in the esophagus, and not as the uncomfortable emptiness that characterizes the genuine pangs of hunger. To be sure, when the gastric hunger contractions are sufficiently intense to be definitely accompanied by esophageal contractions all of us feel the pangs of hunger strongly, but these are of gastric origin and are referred to the stomach and not to the esophagus or throat.
That there is an increase of the tonic contraction of the cardia during the gastric hunger contractions is rendered probable by the fact that the air and other gases always present in the stomach are not forced into the esophagus during these contractions even when they are very strong. Cannon and Washburn state that this fact argues for contractions of the esophagus parallel with the contractions of the empty stomach. Did they not overlook the fact that the cardia is capable of doing this even in the absence of esophageal contractions ? There is no escape of air from the stomach during the periods of incomplete gastric tetanus at the end of a hunger period, although these contractions are practically never accompanied by any esophageal contractions. In the dog esophageal contractions are known to be permanently abolished by section of both vagi, yet this does not lead to belching of air even during the greatest increase in intragastric pressure that the contractions of the empty stomach are capable of producing.
It is therefore evident, not only that the cardia itself is able to prevent the escape of air into the esophagus during increased intragastric pressure, but also that the cardia in all probability contracts more powerfully during the gastric hunger contractions, thus increasing its efficiency as a guard. Direct graphic evidence of the latter is, however, difficult to secure.
When the empty stomach is quiescent the cardia offers only slight resistance to the withdrawal of a distended balloon of the size of a rubber finger cot from the stomach into the esophagus. A larger balloon, such as the condum used for the stomach, encounters somewhat greater resistance at the cardia, as well as in the esophagus itself. If one attempts to withdraw the balloon from the stomach at the height of a gastric hunger contraction, the resistance offered by the cardia is distinctly increased. This can mean only one thing, viz., an increase in the contraction of the cardia. If the contraction of the cardia did not increase, the withdrawal of the balloon would be actually facilitated by the pressure exerted by the stomach contractions. For example, increasing the intragastric pressure by forcible contraction of the abdominal muscles may force the stomach balloon into the esophagus in case the stomach is quiescent.
It is difficult to keep an inflated balloon actually in the cardia for any considerable time, especially during the strongest gastric hunger contractions. Strong esophageal peristaltic movements keep pushing it toward the stomach, and at times the gastric contractions actually push it back into the esophagus. At the best the balloon will stay in the cardia during two or three successive gastric contractions of the weaker type, that is, at the beginning of the hunger period. The type of balloon used for these tests was the rubber finger cot 3 cm. in length. A balloon of greater length could, of course, be lodged in the cardia with greater ease, but a balloon of greater length than 3 cm. would be influenced not only by the cardia, but also by the cardiac ends of the stomach and the esophagus. In fact this probably occurs, but to a less extent, even when a short balloon is used, as the physiological cardia is probably less than 1 cm. in width. Anatomically the cardia is not sharply differentiated in man. We judged the position of the balloon in the cardia by the distance of the balloon from the incisor teeth and by the influence of the respiratory movements, moderate inspiration, mainly costal, causing lowered tension, and moderate diaphragmatic inspiration causing increased tension. When the balloon is in this position the cardia exhibits the 20-seconds rhythm previously reported for the fundus of the empty stomach. This rhythm of the cardia is in evidence even when the empty stomach is quiescent. When the empty stomach shows hunger contractions the cardia shows parallel contractions or periods of increased tonus. The contractions of the fundus and of the cardia are strictly synchronous, but those of the cardia appear to be more persistent or tetanic. The tracings secured by us from the balloon in the cardia resemble those published by Cannon and Washburn as esophageal contractions more than do the actual esophageal contractions obtained by us.
In a few experiments the esophageal balloon was placed in the esophagus 7 to 10 inches from the incisor teeth, that is, in the lower part of the neck and upper part of the chest. The spontaneous local contractions are in evidence also in this part of the esophagus. There is usually a slight increase of tonus when very strong gastric hunger contractions are present, but nothing like the strength of contractions during the peristalsis of deglutition or those caused by the local mechanical stimulation. The tonus increase of the upper half of the esophagus parallel with the gastric contractions is insignificant compared with the corresponding contractions of the lower third of the esophagus. This is probably correlated with the gradual disappearance of non-striated musculature and myenteric plexus in the oral half of the esophagus in man.