In this paper compression-dependent bioimpedance measurements of porcine spleen tissue are presented. Using a Cole-Cole model, nonlinear compositional changes in extracellular and intracellular makeup; related to a loss of fluid from the tissue, are identified during compression. Bioimpedance measurements were made using a custom tetrapolar probe and bioimpedance circuitry. As the tissue is increasingly compressed up to 50%, both intracellular and extracellular resistances increase while bulk membrane capacitance decreases. Increasing compression to 80% results in an increase in intracellular resistance and bulk membrane capacitance while extracellular resistance decreases. Tissues compressed incrementally to 80% show a decreased extracellular resistance of 32%, an increased intracellular resistance of 107%, and an increased bulk membrane capacitance of 64% compared to their uncompressed values. Intracellular resistance exhibits double asymptotic curves when plotted against the peak tissue pressure during compression, possibly indicating two distinct phases of mechanical change in the tissue during compression. Based on these findings, differing theories as to what is happening at a cellular level during high tissue compression are discussed, including the possibility of cell rupture and mass exudation of cellular material.

In this study, a novel thermal management system (TMS) is developed for the minimization of thermal spread created by a monopolar electrosurgical device, the most commonly used surgical instrument. The phenomenon of resistive heating of tissue is modeled using the finite-element method (FEM) to analyze the electrical potential and temperature distributions in biological tissue subjected to heat generation during monopolar electrosurgery. Ex vivo experiments are used to validate the FEM by comparing the model predicted and experimentally measured temperatures. The predicted FEM maximum temperature 1.0 m adjacent to the electrode is within 1% of the experimentally measured maximum temperature using a standard monopolar pencil electrode. A TMS consisting of adjacent cooling channels produces coagulation volumes 80% that of standard monopolar procedures while maintaining comparable temperatures in the targeted tissue below the electrode. In vivo temperatures using a device incorporating a TMS at distances of 2 and 3 m adjacent to the electrode edge are maintained below temperatures known to damage tissue.

This study measures the vascular wall shear rate at the vessel edge using decorrelation based ultrasound speckle tracking. Results for nine healthy and eight renal disease subjects are presented. Additionally, the vascular wall shear rate and circumferential strain during physiologic pressure, pressure equalization and hyperemia are compared for five healthy and three renal disease subjects. The mean and maximum wall shear rates were measured during the cardiac cycle at the top and bottom wall edges. The healthy subjects had significantly higher mean and maximum vascular wall shear rate than the renal disease subjects. The key findings of this research were that the mean vascular wall shear rates and circumferential strain changes between physiologic pressure and hyperemia that was significantly different between healthy and renal disease subjects.

The temporal and spatial tissue temperature profile in electrosurgical vessel sealing was experimentally measured and modeled using finite element modeling (FEM). Vessel sealing procedures are often performed near the neurovascular bundle and may cause collateral neural thermal damage. Therefore, the heat generated during electrosurgical vessel sealing is of concern among surgeons. Tissue temperature in an in vivo porcine femoral artery sealed using a bipolar electrosurgical device was studied. Three FEM techniques were incorporated to model the tissue evaporation, water loss, and fusion by manipulating the specific heat, electrical conductivity, and electrical contact resistance, respectively. These three techniques enable the FEM to accurately predict the vessel sealing tissue temperature profile. The averaged discrepancy between the experimentally measured temperature and the FEM predicted temperature at three thermistor locations is less than 7%. The maximum error is 23.9%. Effects of the three FEM techniques are also quantified.

The bioimpedance of tissues under compression is a field in need of study. While biological tissues can become compressed in a myriad of ways, very few experiments have been conducted to describe the relationship between the passive electrical properties of a material (impedance/admittance) and its underlying mechanical properties (stress and strain) during deformation. Of the investigations that have been conducted, the exodus of fluid from samples under compression has been thought to be the cause of changes in impedance, though until now was not measured directly. Using a soft tissue-mimicking phantom material (tofu) whose passive electrical properties are a function of the conducting fluid held within its porous structure, we have shown that the mechanical behavior of a sample under compression can be measured through bioimpedance techniques.