Propagation speed of sound assessment in the layers of the guinea-pig esophagus in vitro by means of acoustic microscopy

The study's purpose was to evaluate the propagation speed of sound in the tissue layers of the esophagus at various mechanical loadings. Scanning laser acoustics microscopy was applied for the estimation of the propagation speed in the mucosa-submucosa and muscle layers of guinea-pig esophagus in vitro (n = 26). The propagation speed in the esophagus was determined in the no-load state with all external forces removed, and in the distended and zero-stress states. The zero-stress state was obtained by cutting the esophageal rings radially. The propagation speed in the no-load state differed significantly (p < 0.001) between the muscle layer (median 1740, quartiles 1735-1746 m/s) and the mucosa (1607, 1605-1609 m/s). In the distended state the propagation speed in the muscle layer decreased significantly (p < 0.001) to 1673 (1666-1681) m/s while it did not change significantly in mucosa (1602, 1600-1607 m/s). When compared to the no-load state, the propagation speed in the zero-stress state in the muscle layers decreased to 1624 (1615-1636) m/s (p < 0.001) and in mucosa to 1584 (1566-1603) m/s (p < 0.001). In conclusion, the esophagus is a composite structure with heterogeneous propagation speed characteristics. Furthermore, the mechanical loading state must be considered in esophageal ultrasound studies.