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Research Papers

50 Years of Computer Simulation of the Human Thermoregulatory System

[+] Author and Article Information
George M. Netscher

Department of Biomedical Engineering,
The University of Texas at Austin,
Austin, TX 78712

Eugene H. Wissler

Department of Chemical Engineering,
The University of Texas at Austin,
Austin, TX 78712

Kenneth R. Diller

Department of Biomedical Engineering,
The University of Texas at Austin,
Austin, TX 78712
e-mail: kdiller@mail.utexas.edu

1Corresponding author.

Contributed by the Bioengineering Division of ASME for publication in the JOURNAL OF BIOMECHANICAL ENGINEERING. Manuscript received November 10, 2012; final manuscript received December 25, 2012; accepted manuscript posted January 18, 2013; published online February 7, 2013. Editor: Victor H. Barocas.

J Biomech Eng 135(2), 021006 (Feb 07, 2013) (9 pages) Paper No: BIO-12-1548; doi: 10.1115/1.4023383 History: Received November 10, 2012; Revised December 25, 2012; Accepted January 18, 2013

This paper presents an updated and augmented version of the Wissler human thermoregulation model that has been developed continuously over the past 50 years. The existing Fortran code is translated into C with extensive embedded commentary. A graphical user interface (GUI) has been developed in Python to facilitate convenient user designation of input and output variables and formatting of data presentation. Use of the code with the GUI is described and demonstrated. New physiological elements were added to the model to represent the hands and feet, including the unique vascular structures adapted for heat transfer associated with glabrous skin. The heat transfer function and efficacy of glabrous skin is unique within the entire body based on the capacity for a very high rate of blood perfusion and the novel capability for dynamic regulation of blood flow. The model was applied to quantify the absolute and relative contributions of glabrous skin flow to thermoregulation for varying levels of blood perfusion. The model also was used to demonstrate how the unique features of glabrous skin blood flow may be recruited to implement thermal therapeutic procedures. We have developed proprietary methods to manipulate the control of glabrous skin blood flow in conjunction with therapeutic devices and simulated the effect of these methods with the model.

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Figures

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Fig. 1

Graphical representation of the classic Wissler model that terminates at the wrists and ankles. Each of the 25 elements consists of 21 radial layers and 12 angular segments. The new model has four additional elements for two hands and two feet that are highlighted in red.

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Fig. 2

Graphical representation of the control algorithm for normalized glabrous vasodilation (GVD) of Eqs. (1) and (2) that regulates glabrous skin blood flow (GBF). There is a region of intermediate level perfusion associated with thermoneutral control inputs. Increasing core temperature above this region causes a sigmoidal elevation in glabrous perfusion, and decreasing core and mean skin temperatures likewise depresses the perfusion. A minimum level of 5% nutritive blood flow is assumed to be always maintained.

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Fig. 3

GUI screens for specifying input parameters for a thermoregulation process simulation. (a) Physical and physiological data for the subject. (b) AVA blood perfusion levels and control temperatures. (c) Physical activity sequence, types, and durations.

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Fig. 4

Example GUI screen to input clothing type and thermal properties and boundary temperature for each of the 25 model elements

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Fig. 6

Effect on modulation of core temperature as a function of the magnitude of glabrous skin blood flow as a percent of cardiac output (CO) to both hands and both feet with surface cooling at 22  °C. The metabolic protocol consisted of during continuous exposure to air at 23  °C.

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Fig. 5

Simulations by the Wissler and BME models for a male walking for 30 min following equilibration at rest in a thermoneutral environment. (a) Mean skin temperature; (b) skin temperature on thigh; (c) skin temperature on hand (BME model) and end of arm (Wissler model); (d) esophageal temperature.

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