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Research Papers

A High-Resolution Voxel Model for Predicting Local Tissue Temperatures in Humans Subjected to Warm and Hot Environments

[+] Author and Article Information
D. A. Nelson1

 Michigan Technological University, Houghton, MI 49931danelson@usouthal.edu

S. Charbonnel

 Michigan Technological University, Houghton, MI 49931

A. R. Curran, E. A. Marttila

 ThermoAnalytics, Inc., Calumet, MI 49913

D. Fiala

Fachgebiet Bauphysik und Technischer Ausbau, Universität Karlsruhe (TH), 76131 Karlsruhe, Germany

P. A. Mason

Directed Energy Bioeffects Division, Human Effectiveness Directorate, Air Force Research Laboratory, Brooks City-Base, TX 78235

J. M. Ziriax

 Naval Health Research Center Detachment, Brooks City-Base, TX 78235

1

Also at Department of Mechanical Engineering, University of South Alabama, Mobile, AL 36688-0002.

J Biomech Eng 131(4), 041003 (Jan 30, 2009) (12 pages) doi:10.1115/1.3002765 History: Received March 23, 2007; Revised May 09, 2008; Published January 30, 2009

This work describes and presents results from a new three-dimensional whole-body model of human thermoregulation. The model has been implemented using a version of the “Brooks Man” anatomical data set, consisting of 1.3×108 cubic volume elements (voxels) measuring 0.2 cm/side. The model simulates thermoregulation through passive mechanisms (metabolism, blood flow, respiration, and transpiration) and active mechanisms (vasodilatation, vasoconstriction, sweating, and shivering). Compared with lumped or compartment models, a voxel model is capable of high spatial resolution and can capture a level of anatomical detail not achievable otherwise. A high spatial resolution model can predict detailed heating patterns from localized or nonuniform heating patterns, such as from some radio frequency sources. Exposures to warm and hot environments (ambient temperatures of 3348°C) were simulated with the current voxel model and with a recent compartment model. Results from the two models (core temperature, skin temperature, metabolic rate, and evaporative cooling rate) were compared with published experimental results obtained under similar conditions. Under the most severe environmental conditions considered (47.8°C, 27% RH for 2 h), the voxel model predicted a rectal temperature increase of 0.56°C, compared with a core temperature increase of 0.45°C from the compartment model and an experimental mean rectal temperature increase of 0.6°C. Similar, good agreement was noted for other thermal variables and under other environmental conditions. Results suggest that the voxel model is capable of predicting temperature response (core temperature and skin temperature) to certain warm or hot environments, with accuracy comparable to that of a compartment model. In addition, the voxel model is able to predict internal tissue temperatures and surface temperatures, over time, with a level of specificity and spatial resolution not achievable with compartment models. The development of voxel models and related computational tools may be useful for thermal dosimetry applications involving mild temperature hyperthermia and for the assessment of safe exposure to certain nonionizing radiation sources.

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Copyright © 2009 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Core temperatures are shown for each of the four exposure scenarios, as calculated from the voxel model: (a) warm (W), (b) hot (H), (c) very hot (VH), and (d) extremely hot (EH).

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Figure 2

Core temperatures are shown for each of the four exposure scenarios: (a) warm (W), (b) hot (H), (c) very hot (VH), and (d) extremely hot (EH). Voxel model initial temperatures were determined from a simulated 5 h exposure to a thermoneutral environment (30°C, 40% RH, v=0.1 m s−1).

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Figure 3

Color-coded images of tissue temperatures, as predicted for time t=60 min of EH exposure protocol (i.e., after 1 h of thermal equilibration at 27.8°C, 37% RH) using the voxel model: (a) anterior surface view, (b) lateral surface view, (c) midplane coronal section, and (d) midplane sagittal section.

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Figure 4

Color-coded images of tissue temperatures, as predicted for time t=180 min of EH exposure protocol (i.e., after 2 h at 47.8°C, 27% RH) using the voxel model: (a) anterior surface view, (b) lateral surface view, (c) midplane coronal section, and (d) midplane sagittal section

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Figure 5

Skin temperatures for each of the four exposures are shown: (a) warm (W), (b) hot (H), (c) very hot (VH), and (d) extremely hot (EH). Voxel model initial temperatures were determined from a simulated 5 h exposure to a thermoneutral environment (30°C, 40% RH, v=0.1 m s−1).

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Figure 6

Evaporative skin surface heat transfer rates are shown for each of the four exposure scenarios: (a) warm (W), (b) hot (H), (c) very hot (VH), and (d) extremely hot (EH). All values are expressed per unit skin surface area.

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Figure 7

Whole-body metabolic rates are shown for each of the four exposure scenarios: (a) warm (W), (b) hot (H), (c) very hot (VH), and (d) extremely hot (EH). All values are expressed per unit skin surface area.

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