Esophageal function testing: beyond manometry and impedance

Ex-vivo mechano-structural characterization of fresh diseased human esophagus

The esophagus, the tube-like organ responsible for transporting food from the pharynx to the stomach, operates as a highly mechanical structure, exhibiting complex contraction and distension patterns triggered by neurological impulses. Despite the critical role of mechanics in its function and the need for high-fidelity models of esophageal transport, mechanical characterization studies of human esophagus remain relatively scarce. In addition to the paucity of studies in human specimens, the available results are often scattered in terms of methodology and scope, making it difficult to compare findings across studies and thereby limiting their use in computational models. In this work, we present a detailed passive-mechanical and structural characterization of the esophageal muscular layers, excised from short esophageal segments obtained from live patients with varied clinical presentations. Specifically, we conducted uniaxial and planar biaxial extension tests on the smooth muscle layers, complemented by pre- and post-testing structural characterization via histological imaging. Unlike existing studies, our experimental results on passive behavior are discussed in the context of physiological relevance (e.g., physiological stretches, and activity-inhibiting pathologies), providing valuable insights that guide the subsequent modeling of the esophagus' mechanical response. As such, this work provides new insights into the passive properties of the fresh human esophagus, expands the existing database of mechanical parameters for computational modeling, and lays the foundation for future studies on active mechanical properties. STATEMENT OF SIGNIFICANCE: Understanding the mechanical properties of the esophagus is crucial for developing accurate models of its function and suitable replacements. This study provides insights into the passive mechanical behavior of fresh human esophageal tissue, enhancing our understanding of how it responds to stretching under physiological conditions. By characterizing the properties of different esophageal layers, obtained from esophagectomy specimens with various presentations, and considering their relevance to both normal and abnormal functioning, this work addresses the gap in ex-vivo human esophagus studies. The findings emphasize the importance of contextually analyzing experimental results within physiological parameters and suggest avenues for future research to further refine our understanding of esophageal mechanics, paving the way for improved diagnostic and therapeutic approaches in managing esophageal disorders.

Microscopic Anatomy of the Upper Aerodigestive Tract in Harbour Seals (Phoca vitulina): Functional Adaptations to Swallowing

Abandoned harbour seal pups (Phoca vitulina) are frequently recovered by rehabilitation centres and often require intensive nursing, gavage feeding and swallowing rehabilitation prior to anticipated release. Seal upper aerodigestive tract (UAT) histology descriptions relevant to deglutition are limited, impacting advances in rehabilitation practice. Therefore, we examined the histological characteristics of the harbour seal UAT to understand species-specific functional anatomy and characterize adaptations. To this end, we conducted gross dissections, compiled measurements and reviewed histologic features of the UAT structures of 14 pre-weaned harbour seal pups that died due to natural causes or were humanely euthanized. Representative samples for histologic evaluation included the tongue, salivary glands, epiglottis, and varying levels of the trachea and esophagus. Histologically, there was a prominent muscularis in the tongue with fewer lingual papillae types compared to humans. Abundant submucosal glands were observed in lateral and pharyngeal parts of the tongue and rostral parts of the esophagus. When compared to other mammalian species, there was a disproportionate increase in the amount of striated muscle throughout the length of the esophageal muscularis externa. This may indicate a lesser degree of autonomic control over the esophageal phase of swallowing in harbour seals. Our study represents the first detailed UAT histological descriptions for neonatal harbour seals. Collectively, these findings support specific anatomic and biomechanic adaptations relevant to suckling, prehension and deglutition. This work will inform rehabilitation practices and guide future studies on swallowing physiology in harbour seals with potential applications to other pinniped and otariid species in rehabilitation settings. This article is protected by copyright. All rights reserved.