The genesis of bowel sounds: influence of viscus and gastrointestinal content.

This study was undertaken to try to solve the controversy about the influence of gastrointestinal contents on the genesis of bowel sounds, and to probe the respective importance of the various abdominal viscera. Eleven healthy volunteers were intubated by mouth with a multiple-lumen tube. Bowel sounds were recorded for 10 min when the tube was in the stomach, the upper jejunum, and the cecum, while it was left intact in situ, or perfused with isotonic saline (15 ml per min), or with an equal (7.5 ml per min of each) mixture of isotonic saline and air. Using a previously developed method, a computer analysis was made of the recording without any human intervention during the treatment of data. An analysis of variance demonstrated that the effect of perfusion varied according to site, with 46% of counted sounds while the tube was in the stomach, 32% in the jejunum, and 22% in the colon (P less than 0.05). There were two types of sounds: some exceeded in amplitude a preset threshold, and thus were picked up by the computer, but their average absolute value for 20 msec remained inferior to another preset threshold. Their number was kept in memory (NS--sounds having an amplitude exceeding a threshold S1, expressed in number per 10 min). A second type of sounds also exceeded the present threshold but their average absolute value for 20 msec also exceeded another preset threshold. Their number (NE--sounds having an amplitude exceeding the thershold S1 but having also a 20-msec average amplitude above another threshold S2, expressed in number per 10 min) was also memorized. The latter group was composed of two types of sounds: some had a limited spectrum of low frequency (100 Hz) and were of high amplitude and short (congruent to 5 msec) duration (NE1); some others had a higher and more dispersed frequency centered around 300 Hz (NE2). Fifty per cent of high energy (NE) sounds appeared while the tube was in the stomach, 30% in the colon, and 20% in the jejunum (P less than 0.005). Short and high amplitude sounds (NE1) were counted more often (43%) when it was in the colon than in the stomach (38%) and the jejunum (19%) (P less than 0.025), and this was confirmed (P less than 0.005) by a study of the ratio of NE1/NE. On the contrary, higher frequency sounds (NE2) were present more often when the tube was in the stomach (59%) than in the jejunum (24%) and in the colon (17%) (P less than 0.005). There was no influence of the presence of the unperfused tube on the genesis of bowel sounds in different sites (P greater than 0.05). In the stomach and the colon perfusion of the air/saline mixture increased the number of sounds (P less than 0.025) and all types of sounds in the stomach (P less than 0.025), whereas in the jejunum it was the perfusion of saline which increased them (P less than 0.025). It is concluded that the stomach is the most active site of production of bowel sounds, followed by the colon and then the small bowel, that sounds differ in different sites, and that all this is influenced by viscus content.