A heat transfer model of thermal balloon endometrial ablation.

A heat transfer model was developed for thermal balloon endometrial ablation treatment for menorrhagia. The model includes heat conduction through the uterus wall, cooling due to blood perfusion through the uterine tissue and the contribution of metabolic heat generation. A parameter sensitivity study indicated that metabolic heat generation had a minimal effect, but model predictions were sensitive to blood perfusion rate. However, within the range of expected perfusion rates, the model calculates damage depths (3-6 mm) close to the range for effective treatment. Using a blood perfusion rate of 0.0028 m(3)t m(-3)b s(-1), the predicted burn depth (4 mm) correlated well with experimental measurements (4.2 +/- 0.6 mm) reported elsewhere for a treatment temperature of 92 degrees C and time of 6 mins (Neuwirth, R. S. et al. The endometrial ablator: A new instrument. Obstet. Gynecol. 83:792-796, 1994). If no vaporization of water in the tissue occurs, the model predicts that the same burn depth of 4 mm can be obtained with increased treatment temperature (130 degrees C) and shorter treatment time (1.4 min). Steeper temperature profiles through the uterine wall suggest that, in the absence of other changes due to higher temperatures, the deeper layers of the myometrium and the serosa would be protected from thermal damage when using higher treatment temperatures for a shorter duration. However, if vaporization occurs at 105 degrees C, the model predicts little benefit in using treatment temperatures above 120 degrees C up to 160 degrees C. For further validation of the model, in vivo studies using the high temperature treatments are needed to measure temperature profiles through the uterine wall, blood perfusion rates, and the other effects of temperature on uterine tissue.