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Research Papers: Conduction

Thermal Processing of Biological Tissue at High Temperatures: Impact of Protein Denaturation and Water Loss on the Thermal Properties of Human and Porcine Liver in the Range 25–80 °C

[+] Author and Article Information
John C. Bischof

e-mail: bischof@umn.edu
Department of Mechanical Engineering,
University of Minnesota,
Minneapolis, MN 55455

1Corresponding author.

Manuscript received October 15, 2012; final manuscript received January 26, 2013; published online May 16, 2013. Assoc. Editor: Leslie Phinney.

J. Heat Transfer 135(6), 061302 (May 16, 2013) (7 pages) Paper No: HT-12-1566; doi: 10.1115/1.4023570 History: Received October 15, 2012; Revised January 26, 2013

Biothermal engineering applications impose thermal excursions on tissues with an ensuing biological outcome (i.e., life or death) that is tied to the molecular state of water and protein in the system. The accuracy of heat transfer models used to predict these important processes in turn depends on the kinetics and energy absorption of molecular transitions for both water and protein and the underlying temperature dependence of the tissue thermal properties. Unfortunately, a lack of tissue thermal property data in the literature results in an overreliance on property estimates. This work addresses these thermal property limitations in liver, a platform tissue upon which hyperthermic engineering applications are routinely performed and a test bed that will allow extension to further tissue property measurement in the future. Specifically, we report on the thermal properties of cadaveric human and porcine liver in the suprazero range between 25 °C to 80 °C for thermal conductivity and 25 °C to 85 °C for apparent specific heat. Denaturation and water vaporization are shown to reduce thermal conductivity and apparent specific heat within the samples by up to 20% during heating. These changes in thermal properties significantly altered thermal histories during heating compared to conditions when properties were assumed to remain constant. These differences are expected to alter the biological outcome from heating as well.

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Figures

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Fig. 1

Representative thermal conductivity values of (a) human and (b) animal tissues available in the literature in the suprazero temperature range

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Fig. 2

Electrical response of thermistor probe during thermal conductivity measurements. Measured results are shown for two time intervals (black: 2–10 s, gray: 10–50 s) with their respective linear fits.

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Fig. 3

Thermal conductivity of (a) porcine and (b) human liver (n = 7, both). Values are mean +/− standard error (*, p < 0.05).

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Fig. 4

Apparent specific heat of (a) porcine and (b) human liver (n > 3). Values are mean +/− standard error.

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Fig. 5

Change in mass fraction of water for porcine liver

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Fig. 6

Predicted thermal conductivity of (a) porcine and (b) human liver for different heating conditions

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Fig. 7

Predicted thermal histories of heating porcine liver under different heating conditions, (a) temporal and (b) axial, where α25 is the thermal diffusivity of the sample at 25  °C

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