Clarifying changes in gastrointestinal tissue compressed by surgical stapler is a crucial prerequisite for stapler design optimization. For this study, a stapler was modified, and multifrequency bioimpedance of a porcine small intestine tissue compressed by the stapler was measured. The Cole Y model was fitted to the bioimpedance, and changes in tissue were analyzed using model parameters: G 0, extracellular fluid conductance; ΔG, intracellular fluid conductance; C cpeF, equivalent capacitance of cell membrane. The changes could be divided into two stages: first, all parameters decreased sharply with slopes more than 15.70 ± 2.67, 4.25 ± 1.23 μS/s and 72.68 ± 6.99 pF/s respectively; and subsequently, with an increase in compression strength, G 0 decreased with slopes less than 2.54 ± 0.40 μS/s, ΔG decreased slightly with slope of 0.26 ± 0.04 μS/s after fluctuating mildly, and C cpeF remained nearly invariant after initially increasing with slope of -2.94 ± 0.64 pF/s. In conclusion, when the stapler is closed, a portion of tissue is squeezed out of the measurement space, causing all parameters' sharp decrease. Subsequently, the stapler continues compressing the tissue, leading to extracellular fluid expulsion. The changes in intracellular fluid are related to the compression strength and may be explained by cell restoration. This study could provide a basis for stapler design optimization.
Keywords: Cole Y model; Extracellular fluid; Intracellular fluid; Multifrequency bioimpedance; Stapler; Tissue compression.