Limitations of implantable, miniature ultrasonic transducers to measure wall movement in the canine jejunum

Background. We used implantable miniature ultrasonic transducers to measure longitudinal distance, circumference, and wall thickness dynamically in vivo in canine jejunum. We hoped to differentiate circular from longitudinal smooth muscle contractions and to correlate physical measurements of change in distance within the jejunal wall with intraluminal manometry. Materials and methods. In acute experiments at the time of celiotomy, longitudinal distances, circumferences, and wall thickness were measured directly and by ultrasonic transducers sewn to serosa and mucosa. Measurements were obtained with the intestine empty and after distention with air, water, or semisolid slurry. In chronic in vivo experiments in conscious dogs with indwelling ultrasonic transducers and intraluminal manometers, sonometric dimensions were correlated with manometric recordings. In acute experiments, sonometric measurements were similar to direct measurements. In chronic experiments in vivo, smallest ultrasonometric measurements of circumferences of the jejunum correlated in a phase-locked temporal manner with both highest intraluminal pressures and greatest wall thickness. Results. Longitudinal distances increased during decreases in circumference. Distances orad to the site maximal intraluminal pressure peaked at 0.58 ± 0.04 s (x̄ ± SEM) before, and those aborad to this point 0.42 ± 0.04 s after attaining minimum circumferences. Conclusions Ultrasonic crystals can monitor geometric changes in the bowel wall with certain limitations, especially when obtained in vivo. Contraction of circular and longitudinal muscles, although phase-locked, do not appear to occur exactly synchronously in canine jejunum.