Endometrial Thermal Balloon Ablation Using a High Temperature, Pulsed System: A Mathematical Model

[+] Author and Article Information
Daniel M. Reinders, Susan A. Baldwin, Joel L. Bert

Department of Chemical and Biological Engineering, University of British Columbia, 2216 Main Mall, Vancouver, B.C. V6T 1Z4, Canada

J Biomech Eng 125(6), 841-851 (Jan 09, 2004) (11 pages) doi:10.1115/1.1634279 History: Received September 16, 2002; Revised June 23, 2003; Online January 09, 2004
Copyright © 2003 by ASME
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Illustration of the high temperature, pulsed thermal balloon ablation method. During each pulse cycle fluid is transferred between the reservoir and the balloon. 1. During the deflation period a small, residual volume of fluid remains in the balloon. 2. When fluid is pumped into the balloon, the uterus expands to its natural volume. 3. When the balloon pressure reaches 180 mmHg, the uterus is further distended and occlusion of blood vessels adjacent to the balloon occurs. The increase in inner cavity radius, ri, from ri, the inner cavity radius of the un-stressed uterus at its natural volume is small (<1 mm).
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Photograph of a sectioned uterus following treatment with the Thermablate™ EAS™. The tissue was stained with NBT, where the absence of stain indicates thermal damage. Note the presence of the red zone.
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Temperature history recorded during an in vitro experiment using a 16 mL cavity. Points are temperatures measured by thermocouples placed in middle of the balloon, at the surface of the uterus cavity, 2 and 5 mm into the tissue. The lines represent the model predictions that best fit the balloon and uterus cavity surface temperatures using the parameter values given in Table 2.
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(a) and (b) Sample in vitro experiment data used for model validation. A 26 mL cavity volume was used for Fig. 4a and a 5 mL volume was used for Fig. 4b. Points are temperatures measured by thermocouples placed in middle of the balloon, at the surface of the uterus cavity, 2 and 5 mm into the tissue. The cavity surface temperature was measured in two locations (TC1 and TC2). The lines represent the model predictions using the parameter values given in Table 2. These figures illustrate accuracy of the model when applied to different cavity volumes.
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Measured (data points) and model predicted (line) maximum cavity surface temperatures (°C) for the in vitro experiments as a function of cavity volume (mL).
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Measured (clinical trials) and calculated alpha and beta burn depths as a function of distended uterine cavity volume. The solid line represents the calculated alpha burn (immediate tissue necrosis) depth. The dashed line represents the calculated beta burn (eventual tissue necrosis) depth. The points are burn depths measured during clinical trials using the high temperature, pulsed treatment. These were measured using NBT stain (open squares) and H&E stain (open circles). In one case, the depth of the red zone was measured (solid square).
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Comparison of calculated burn depth dependence on uterine cavity volume between the low temperature (75°C for 15 min) (dashed lines) and high temperature, pulsed (173°C for 2 min) (solid lines) treatments. Heavy lines are the alpha burn and light lines the beta burn.
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Values of the blood perfusion multiplication factor, f(r,t), versus distance from the uterine cavity surface (mm) during (1 and 2 min) and after (3 min) treatment. The balloon pressure eliminates blood perfusion to 6 mm (point A) and reduces perfusion below normal through the rest of the tissue. Blood perfusion increases with time due to hyperemia, but only marginally. After treatment, blood perfusion increases markedly except in the first 4 mm where blood perfusion stasis has occurred due to thermal damage.
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Contour diagrams of treatment uterine cavity surface temperature and times that yield the same alpha (a) and beta (b) burn depths. Treatment temperatures were held constant for the duration of treatment. Contours represent accumulated burn depths calculated by the model.




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