A high-resolution voxel model for predicting local tissue temperatures in humans subjected to warm and hot environments.

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 1.3x10(8) 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 33-48 degrees 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 degrees C, 27% RH for 2 h), the voxel model predicted a rectal temperature increase of 0.56 degrees C, compared with a core temperature increase of 0.45 degrees C from the compartment model and an experimental mean rectal temperature increase of 0.6 degrees 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.

Human projected area factors for detailed direct and diffuse solar radiation analysis.

Projected area factors for individual segments of the standing and sedentary human body were modelled for both direct and diffuse solar radiation using detailed 3D geometry and radiation models. The local projected area factors with respect to direct short-wave radiation are a function of the solar azimuth angle (alpha) between 0 degrees < alpha<360 degrees and the solar altitude (beta) angles between -90 degrees < beta<+90 degrees . In case of diffuse solar radiation from the isotropic sky the local human projected area factors were modelled as a function of the ground albedo (rho) ranging between 0< rho<1. The model was validated against available experimental data and showed good general agreement with projected area factors measured for both the human body as a whole and for local quantities. Scientists can use the equations to predict the inhomogeneous irradiation and absorption of direct and diffuse solar radiation and UV-radiation at surfaces of the human body. In conjunction with detailed multi-node models of human thermoregulation the equations can be used to predict the physiological implications of solar radiation and outdoor weather conditions on humans.

Modelling fire-fighter responses to exercise and asymmetric infrared radiation using a dynamic multi-mode model of human physiology and results from the sweating agile thermal manikin.

In this study, predicted dynamic physiological responses are compared with wear trials results for firefighter suits: impermeable (A), semi-permeable (B) and permeable (C), and underwear. Wear trials consisted of three rest phases and two moderate work phases, with a frontal infrared (IR) radiation exposure of 500 W/m2 for the last 15 min of each work phase. Simulations were performed by detailed modelling of the experimental boundary conditions, including the inhomogeneous IR radiation combined with clothing properties for still and walking conditions measured using the Sweating Agile thermal Manikin. Accounting for the effect of sweat gland activity suppression with increased skin wettedness, the predicted total moisture loss was insignificantly different (P<0.05) from the wear trial value for suits B and C but was 37% too high for suit A. Predicted evolution of core, mean skin and local skin temperatures agreed well with the wear trial results for all clothing. Root mean square deviations ranged from 0.11 degrees C to 0.26 degrees C for core temperatures and from 0.28 degrees C to 0.38 degrees C for mean skin temperatures, which where typically lower than the experimental error. Transient thermodynamic processes occurring within suit A may account for the delayed/reduced fall in core temperature following exercise.

Computer prediction of human thermoregulatory and temperature responses to a wide range of environmental conditions.

A mathematical model for predicting human thermal and regulatory responses in cold, cool, neutral, warm, and hot environments has been developed and validated. The multi-segmental passive system, which models the dynamic heat transport within the body and the heat exchange between body parts and the environment, is discussed elsewhere. This paper is concerned with the development of the active system, which simulates the regulatory responses of shivering, sweating, and peripheral vasomotion of unacclimatised subjects. Following a comprehensive literature review, 26 independent experiments were selected that were designed to provoke each of these responses in different circumstances. Regression analysis revealed that skin and head core temperature affect regulatory responses in a nonlinear fashion. A further signal, i.e. the rate of change of the mean skin temperature weighted by the skin temperature error signal, was identified as governing the dynamics of thermoregulatory processes in the cold. Verification and validation work was carried out using experimental data obtained from 90 exposures covering a range of steady and transient ambient temperatures between 5 degrees C and 50 degrees C and exercise intensities between 46 W/m2 and 600 W/m2. Good general agreement with measured data was obtained for regulatory responses, internal temperatures, and the mean and local skin temperatures of unacclimatised humans for the whole spectrum of climatic conditions and for different activity levels.

A computer model of human thermoregulation for a wide range of environmental conditions: the passive system.

A dynamic model predicting human thermal responses in cold, cool, neutral, warm, and hot environments is presented in a two-part study. This, the first paper, is concerned with aspects of the passive system: 1) modeling the human body, 2) modeling heat-transport mechanisms within the body and at its periphery, and 3) the numerical procedure. A paper in preparation will describe the active system and compare the model predictions with experimental data and the predictions by other models. Here, emphasis is given to a detailed modeling of the heat exchange with the environment: local variations of surface convection, directional radiation exchange, evaporation and moisture collection at the skin, and the nonuniformity of clothing ensembles. Other thermal effects are also modeled: the impact of activity level on work efficacy and the change of the effective radiant body area with posture. A stable and accurate hybrid numerical scheme was used to solve the set of differential equations. Predictions of the passive system model are compared with available analytic solutions for cylinders and spheres and show good agreement and stable numerical behavior even for large time steps.

Continued cost justification of an operating room satellite pharmacy.

Cost justification for the establishment and continued operation of an operating room satellite pharmacy is described. Establishment of an operating room satellite pharmacy can be justified based on the need to recover lost revenue, regulate controlled substances, monitor inventory, and enhance communication between operating room personnel and the department of pharmacy. At a 510-bed community hospital, an internal audit performed before the satellite pharmacy was opened revealed an average loss of $14.53 in drug charges per surgical procedure; 16 months after the pharmacy opened, changes in the way drugs are distributed to the departments of surgery and anesthesia has resulted in a decrease in this loss to $9.61, or a 34% improvement. To regulate controlled substances, the pharmacy attaches a drug-use log to each dispensing kit, which has resulted in 98% agreement between recorded administration of controlled substances and actual amounts signed out and ultimately returned. Recommendations made by the department of pharmacy regarding the use of high-cost drugs during surgery has resulted in an annual savings of more than $100,000, and improvements in drug packaging reduced, and in some cases eliminated, wastage. Direct contact between operating room personnel and pharmacists has fostered discussions regarding cost-effective application of pharmacotherapy, and the potential for cost savings is substantial. Although the remaining loss of $9.61 per case must still be addressed, considerable progress has been made in a relatively short period of time. The satellite pharmacy in the operating room has led to increased revenue recovery, improved regulation of controlled substances and monitoring of drug inventory, and better communication among the involved personnel.