Metabolic Heat Generation Research Articles

Three-dimensional finite element model to study temperature distribution in peripheral layers of human limbs immediately after physical exercise

The physical exercise imposes challenges on the human thermoregulatory system, as heat exchange between the body and environment is substantially impaired, which can lead to decrease in performance and increased risk of heat illness. In view of above a three-dimensional finite element model is proposed to study the effect of different intensities of physical exercise on temperature distribution in peripheral regions of human limbs under moderate climatic conditions. Human limb is assumed to have a cylindrical cross-section. The peripheral region of the human limb is divided into three natural components, namely epidermis, dermis and subdermal tissues. The model incorporates the effect of important physiological parameters like blood mass flow rate, metabolic heat generation, and thermal conductivity of the tissues. Appropriate boundary conditions have been framed based on the physical conditions of the problem. The model is transformed into the discretized variational form and finite element method (FEM) has been employed to obtain the solution. The numerical results have been used to obtain the temperature profiles in the region immediately after exercise for an unsteady state case. The thermal information generated from the model can be useful for developing protocols for improving performance of sportsmen, military persons and labor-intensive workers.

A 3D thermal model to analyze the temperature changes of digits during cold stress and predict the danger of frostbite in human fingers

The existing computational models of frostbite injury are limited to one and two dimensional schemes. In this study, a coupled thermo-fluid model is applied to simulate a finger exposed to cold weather. The spatial variability of finger-tip temperature is compared to experimental ones to validate the model. A semi-realistic 3D model for tissue and blood vessels is used to analyze the transient heat transfer through the finger. The effect of heat conduction, metabolic heat generation, heat transport by blood perfusion, heat exchange between tissues and large vessels are considered in energy balance equations. The current model was then tested in different temperatures and air speeds to predict the danger of frostbite in humans for different gloves. Two prevalent gloves which are commonly used in cold climate are considered for investigation. The endurance time and the fraction of necrotic tissues are two main factors suggested for obtaining the response of digit tissues to different environmental conditions.

A simple method for the measurement of metabolic heat production rates during solid-state fermentations using β-carotene production with Blakeslea trispora as a model system.

Solid-state fermentation (SSF) technology has been rapidly developed for the past 10 years as a production platform for secondary metabolites, biofuels, food, and pharmaceuticals. Yet, the main drawback of SSF is the local temperature rise of up to 20 K, which potentially reduces the strain activity and inactivates heat sensible products. Due to the low heat capacity and thermal conductivity of mixtures of air with plant material, in comparison to aqueous suspensions in submerged fermentations, heat from metabolic processes is less efficiently dissipated. The exact knowledge of the metabolic heat generation during SSF processes is crucial to guide strategies against overheating. In this work, a simple method using a cost-efficient multichannel instrument is proposed, which allows the determination of heat generation during SSF processes. This method was successfully tested and validated with Blakeslea trispora producing β-carotene during growth on barley. Additionally, the consequences of the generated metabolic heat during SSF on temperature rise and water evaporation were discussed. Finally, changes in growth and product concentration could also be detected by the heat signal, implying the potential as a timesaving screening method.

One Dimensional Transient State Finite Element Model to Study Thermal Variations due to Transient Vasoconstriction followed by Persistent Vasodilation during Inflammation in Surgical Wound of Peripheral Tissues of Human Limb

Objectives: This paper compares theoretically the thermal variations in normal tissues, clean surgical wound and contaminated surgical wound in peripheral tissues of human arm and leg during inflammatory phase of healing. Methods/Statistical Analysis: One dimensional finite element model is developed using Bio-heat equation.Values of arterial blood temperature, core body temperature and heat transfer coefficient have been revised. During inflammation blood perfusion rate and metabolic heat generation rate are considered linearly dependent on temperature and spatial coordinate, and exponentially dependent on time.The effect of vasodilation and effect of rate at which vascular changes occur, on temperature profiles,is investigated by varying value of linear coefficient of temperature dependence and coefficient of time variable respectively. Findings: A computer programme in MATLAB is developed to simulate the results. Skin surface temperature in normal tissue are simulated and validated from published experimental data. Maximum blood perfusion rate at maximum vasodilation calculated theoretically is validated with the published experimental data. Temperature difference in contaminated wound and normal tissue are simulated and validated with the published experimental data. Improvements/Applications: Normal skin temperature and thermal variations during vasodilation are modelled well by revising the values of parameters mentioned above and considering temperature dependent parameters.This information may be useful to biomedical scientists in development of treatment regimen for surgical wounds.

One Dimensional Transient State Finite Element Model to Study Thermal Variations due to Transient Vasoconstriction followed by Persistent Vasodilation during Inflammation in Surgical Wound of Peripheral Tissues of Human Limb

Objectives: This paper compares theoretically the thermal variations in normal tissues, clean surgical wound and contaminated surgical wound in peripheral tissues of human arm and leg during inflammatory phase of healing. Methods/ Statistical Analysis: One dimensional finite element model is developed using Bio-heat equation.Values of arterial blood temperature, core body temperature and heat transfer coefficient have been revised. During inflammation blood perfusion rate and metabolic heat generation rate are considered linearly dependent on temperature and spatial coordinate, and exponentially dependent on time.The effect of vasodilation and effect of rate at which vascular changes occur, on temperature profiles,is investigated by varying value of linear coefficient of temperature dependence and coefficient of time variable respectively. Findings: A computer programme in MATLAB is developed to simulate the results. Skin surface temperature in normal tissue are simulated and validated from published experimental data. Maximum blood perfusion rate at maximum vasodilation calculated theoretically is validated with the published experimental data. Temperature difference in contaminated wound and normal tissue are simulated and validated with the published experimental data. Improvements/Applications: Normal skin temperature and thermal variations during vasodilation are modelled well by revising the values of parameters mentioned above and considering temperature dependent parameters.This information may be useful to biomedical scientists in development of treatment regimen for surgical wounds. Keywords: Finite Element Technique ,Non-linear Partial Differential Equation,, Temperature Dependent Blood Perfusion Rate, Temperature Dependent Metabolic Heat Generation Rate, Thermal Variations in Peripheral Tissues of Human Limb, Vasodilation

Multi-parametric study of temperature and thermal damage of tumor exposed to high-frequency nanosecond-pulsed electric fields based on finite element simulation

High-frequency nanosecond-pulsed electric fields were recently introduced for tumor or abnormal tissue ablation to solve some problems of conventional electroporation. However, it is necessary to study the thermal effects of high-field-intensity nanosecond pulses inside tissues. The multi-parametric analysis performed here is based on a finite element model of liver tissue with a tumor that has been punctured by a pair of needle electrodes. The pulse voltage used in this study ranges from 1 to 4 kV, the pulse width ranges from 50 to 500 ns, and the repetition frequency is between 100 kHz and 1 MHz. The total pulse length is 100 μs, and the pulse burst repetition frequency is 1 Hz. Blood flow and metabolic heat generation have also been considered. Results indicate that the maximum instantaneous temperature at 100 µs can reach 49 °C, with a maximum instantaneous temperature at 1 s of 40 °C, and will not cause thermal damage during single pulse bursts. By parameter fitting, we can obtain maximum instantaneous temperature at 100 µs and 1 s for any parameter values. However, higher temperatures will be achieved and may cause thermal damage when multiple pulse bursts are applied. These results provide theoretical basis of pulse parameter selection for future experimental researches.

Numerical simulation of dual-phase-lag bioheat transfer model during thermal therapy

This paper theoretically investigates the thermal behavior in a living biological tissue under various coordinate systems and different non-Fourier boundary conditions with the dual-phase-lag bioheat transfer model during thermal therapy. The properties of Legendre wavelets together with the finite difference scheme are used to find an approximate analytical solution of the present problem. It has been observed that surrounding healthy tissues are less affected in second and third kind of boundary condition when applied along with spherical symmetric coordinate system. Also greater temperature rise and fast achievement of peak hyperthermia temperature is achieved when second and third kind of boundary conditions are used in combination with Cartesian coordinate system. It is observed that due to the presence of blood perfusion and temperature dependent metabolic heat generation term, the dual-phase-lag bioheat transfer model reduces to Pennes bioheat transfer model only when τq=τT=0s, not for arbitrary τq=τT. Further, in case of dual-phase-lag bioheat transfer model wave-like or diffusion-like behavior will dominate depends whether the ratio τq/τT > 1 or τq/τT < 1. Effect of temperature dependent metabolic heat generation rate, thermal conductivity and blood perfusion rate on dimensionless temperature are discussed in details. The whole analysis is presented in dimensionless form.

Symposium: Animal welfare challenges for today and tomorrow

The increasing separation of the public from production agriculture means there is often a lack of knowledge among consumers about current production practices and a perception that increased productivity and economic efficiency are necessarily associated with a decline in animal welfare. A symposium was organized to present information about animal welfare issues and the challenges they pose for both scientists and the poultry and allied industries. Companion papers provide information about understanding public attitudes and physiological/immunological approaches to welfare assessment, while this paper outlines current and future challenges to egg and meat production and industry responses to those challenges. For broiler chickens, increases in growth rate result in corollary increases in metabolic heat generation and water consumption, leading to the need for continuing improvements in housing, ventilation, and litter management. Stocking densities, lighting programs, muscle myopathies, and use of antibiotics are also areas that require research attention. In the layer industry, the key challenge is housing, with the industry undergoing a shift from conventional cage housing to alternatives like enriched colonies or cage-free. While these alternative systems have hen welfare advantages, there are also welfare disadvantages that require the development of mitigation strategies, and it is also essential to address associated issues including economic, environmental, egg safety, and worker health impacts. Concerns on the horizon include euthanasia of surplus male chicks and spent hens as well as beak-trimming. The humaneness of slaughter methods is an important welfare and consumer confidence issue, and the current regulations for poultry slaughter in the USA are discussed and compared to those for livestock. The poultry and allied industries, including retailers, are responding to these concerns by consulting with experts, developing science-based animal care standards and auditing programs, strengthening training and oversight programs, promoting research, and improving communication channels. In future, intensifying multi-disciplinary research efforts and developing mechanisms to improve communication between scientists and stakeholders, including the public, will be critical to addressing these issues.

TEMPERATURE DISTRIBUTION AND THERMAL DAMAGE OF PERIPHERAL TISSUE IN HUMAN LIMBS DURING HEAT STRESS: A MATHEMATICAL MODEL

The physiological processes taking place in human body are disturbed by the abnormal changes in climate. The changes in environmental temperature are not effective only to compete with thermal stability of the system but also in the development of thermal injuries at the skin surfaces. Therefore, it is of great importance to estimate the temperature distribution and thermal damage in human peripherals at extreme temperatures. In this paper, the epidermis, dermis and subcutaneous tissue were modeled as uniform elements with distinct thermal properties. The bioheat equation with appropriate boundary conditions has been used to estimate the temperature profiles at the nodal points of the skin and subcutaneous tissue with variable ambient heat and metabolic activities. The model has been solved by variational finite element method and the results of the changes in temperature distribution of the body and the damage to the exposed living tissues has been interpreted graphically in relation with various atmospheric temperatures and rate of metabolic heat generation. By involving the metabolic heat generation term in bioheat equation and using the finite element approach the results obtained in this paper are more reasonable and appropriate than the results developed by Moritz and Henriques, Diller and Hayes, and Jiang et al.

Finite element model to study temperature distribution in skin and deep tissues of human limbs

The temperature of body tissues is viewed as an indicator of tissue response in clinical applications since ancient times. The tissue temperature depends on various physical and physiological parameters like blood flow, metabolic heat generation, thermal conductivity of tissues, shape and size of organs etc. In this paper a finite element model has been proposed to study temperature distribution in skin and deep tissues of human limbs. The geometry of human limb is taken as elliptical tapered shape. It is assumed that outer surface of the limb is exposed to the environment. The appropriate boundary conditions have been framed based on physical conditions of the problem. The model has been developed for a three dimensional steady state case. Hexahedral circular sectoral elements are used to discretize the region. The results have been computed to obtain temperature profiles and study the relation of tissue temperature with the parameters like atmospheric temperature, rate of evaporation, thickness of tissues layers and shape of the limb.

Non-linear dual-phase-lag model for analyzing heat transfer phenomena in living tissues during thermal ablation

In this article, a non-linear dual-phase-lag (DPL) bio-heat transfer model based on temperature dependent metabolic heat generation rate is derived to analyze the heat transfer phenomena in living tissues during thermal ablation treatment. The numerical solution of the present non-linear problem has been done by finite element Runge-Kutta (4,5) method which combines the essence of Runge-Kutta (4,5) method together with finite difference scheme. Our study demonstrates that at the thermal ablation position temperature predicted by non-linear and linear DPL models show significant differences. A comparison has been made among non-linear DPL, thermal wave and Pennes model and it has been found that non-linear DPL and thermal wave bio-heat model show almost same nature whereas non-linear Pennes model shows significantly different temperature profile at the initial stage of thermal ablation treatment. The effect of Fourier number and Vernotte number (relaxation Fourier number) on temperature profile in presence and absence of externally applied heat source has been studied in detail and it has been observed that the presence of externally applied heat source term highly affects the efficiency of thermal treatment method.

Thermal stability of biological tissues and their behavior in cold conditions — A mathematical model

This paper presents an application of finite element method to study the thermoregulatory behavior of three layers of human dermal parts with varying properties. The investigation of temperature distributions in epidermis, dermis and subcutaneous tissue together with Crank–Nicholson scheme at various atmospheric conditions was carried out. The finite element method has been applied to obtain the numerical solution of governing differential equation for one-dimensional unsteady state bioheat equation using suitable values of parameters that affect the heat transfer in human body. The outer skin is assumed to be exposed to cold atmospheric temperatures and the loss of heat due to convection, radiation and evaporation has been taken into consideration. The important parameters like blood mass flow rate, metabolic heat generation rate and thermal conductivity are taken heterogeneous in each layer according to their distinct physiological and biochemical activities. The temperature profiles at various nodal points of the skin and in vivo tissues have been calculated with respect to the severe cold ambient temperatures. The conditions under which hypothermia, non-freezing and freezing injuries develop were illustrated in the graphs.

Parameter estimation of breast tumour using dynamic neural network from thermal pattern

This article presents a new approach for estimating the depth, size, and metabolic heat generation rate of a tumour. For this purpose, the surface temperature distribution of a breast thermal image and the dynamic neural network was used. The research consisted of two steps: forward and inverse. For the forward section, a finite element model was created. The Pennes bio-heat equation was solved to find surface and depth temperature distributions. Data from the analysis, then, were used to train the dynamic neural network model (DNN). Results from the DNN training/testing confirmed those of the finite element model. For the inverse section, the trained neural network was applied to estimate the depth temperature distribution (tumour position) from the surface temperature profile, extracted from the thermal image. Finally, tumour parameters were obtained from the depth temperature distribution. Experimental findings (20 patients) were promising in terms of the model’s potential for retrieving tumour parameters.

Thermal stress, human performance, and physical employment standards.

Many physically demanding occupations in both developed and developing economies involve exposure to extreme thermal environments that can affect work capacity and ultimately health. Thermal extremes may be present in either an outdoor or an indoor work environment, and can be due to a combination of the natural or artificial ambient environment, the rate of metabolic heat generation from physical work, processes specific to the workplace (e.g., steel manufacturing), or through the requirement for protective clothing impairing heat dissipation. Together, thermal exposure can elicit acute impairment of work capacity and also chronic effects on health, greatly contributing to worker health risk and reduced productivity. Surprisingly, in most occupations even in developed economies, there are rarely any standards regarding enforced heat or cold safety for workers. Furthermore, specific physical employment standards or accommodations for thermal stressors are rare, with workers commonly tested under near-perfect conditions. This review surveys the major occupational impact of thermal extremes and existing employment standards, proposing guidelines for improvement and areas for future research.

Estimation of growth features and thermophysical properties of melanoma within 3-D human skin using genetic algorithm and simulated annealing

A study has been performed on human skin model with the motivation to device an effective non-invasive modality to characterize the subsurface skin cancer features such as tumor diameter, penetration depth, blood perfusion and metabolic heat generation based on the thermal response of the skin surface obtained from the thermal images. The work presents the role of data mining algorithms to find the tumor features underneath the skin based on the surface temperature variations obtained from a 3-D model of human skin. The human skin is assumed to be subjected to combined radiative, convective, and evaporative heat flux boundary conditions. The study revealed that, the major variation in the thermal response of tumor is attributed to increase in the volume, blood perfusion and thermogenic capacity. The variations due to inter- and intra-patient variability of tumor properties and size are obvious, which could be explained by the retrieved multiple combinations of variables. Furthermore, the reconstructed surface thermal distributions associated with estimated variables are found to be in a good match with the actual maps. The error <10% in the measured thermal distribution tends to give accurate reconstruction. Present strategy or algorithm along with a thermal camera may prove to be a useful diagnostic tool for the characterization of subsurface skin cancer and reduce the unnecessary biopsy trials.

An efficient technique for estimating the two-dimensional temperature distributions around multiple cryo-surgical probes based on combining contributions of unit circles

This study presents an efficient, fast and accurate method for estimating the two-dimensional temperature distributions around multiple cryo-surgical probes. The identical probes are inserted into the same depth and are operated simultaneously and uniformly. The first step in this method involves numerical derivation of the temporal performance data of a single probe, embedded in a semi-infinite, tissue-like medium. The results of this derivation are approximated by algebraic expressions that form the basis for computing the temperature distributions of multiple embedded probes by combining the data of a single probe. Comparison of isothermal contours derived by this method to those computed numerically for a variety of geometrical cases, up to 15 inserted probes and 2–10 min times of operation, yielded excellent results. Since this technique obviates the solution of the differential equations of multiple probes, the computational time required for a particular case is several orders of magnitude shorter than that needed for obtaining the full numerical solution. Blood perfusion and metabolic heat generation rates are demonstrated to inhibit the advancement of isothermal fronts. Application of this method will significantly shorten computational times without compromising the accuracy of the results. It may also facilitate expeditious consideration of the advantages of different modes of operation and the number of inserted probes at the early design stage.

Computational modelling of neonate’s brain cooling

Purpose – The purpose of this paper is to present the computational model of the neonate’s brain cooling process. The main aim of the analysis is to tune the developed computational model, make it convergent and representing the hypothermia therapy reasonably. To find the appropriate model parameters the trial of an inverse analysis, based on the standard least-square method, is performed. Having partially validated model the number of numerical simulations are carried out to compare their results with measurements made during real therapy. Design Methodology Approach – The geometrical model of the newborn’s body is built using MRI and CT scans utilizing Mimics software and the Design Modeler while Ansys Fluent with its User Defined Function capability was used to implement the whole model and to carry out simulations. To model the bioheat transfer the Pennes bioheat equation is applied. In the mathematical model blood perfusion rate, metabolic heat generation rate as well as the arterial blood temperatur...

Studying the effects of the heat stress on the various layers of human skin using damage function

This paper develops a model to identify the effects of thermal stress on temperature distribution and damage in human dermal regions. The design and selection of the model takes into account many factors effecting the temperature distribution of skin, e.g., thermal conductance, perfusion, metabolic heat generation and thermal protective capabilities of the skin. The transient temperature distribution within the region is simulated using a two-dimensional finite element model of the Pennes’ bioheat equation. The relationship between temperature and time is integrated to view the damage caused to human skin by using Henriques’ model Henriques, F. C., Arch. Pathol. 43 (1947) 489–502]. The Henriques’ damage model is found to be more desirable for use in predicting the threshold of thermal damage. This work can be helpful in both emergency medicines as well as to plastic surgeon in deciding upon a course of action for the treatment of different burn injuries.

Experimental and numerical investigation of heat confinement during nanoparticle-assisted thermal therapy

Nanoparticle-assisted thermal ablation therapy has recently evolved as a promising future therapy for cancer treatment. This therapy is advantageous because it is potentially much more selective than traditional methods (surgery or chemotherapy) in terms of destroying cancerous cells while leaving healthy tissue intact. In this study, heat confinement and thus the healthy tissue sparing characteristics, were experimentally investigated. Two Agarose gel samples of cylindrical shape were synthesized for evaluating the heat confinement in the axial and radial directions. A specified region of the gel was embedded with gold nanoparticles which were synthesized in this study (mimicking an injection of nanoparticles to the tumor region), while the rest of the plain gel mimics the surrounding healthy tissue. These Agarose gel samples were irradiated through fiber optic and the spatiotemporal temperature response was measured. A numerical model was also developed and validated against these experiments. The measurements were then extended to real tumor-tissue by taking into account blood perfusion and metabolic heat generation. It is observed that with the proposed approach, heat can be well confined to the nanoparticle embedded region. This study shows that with a well-designed system it is possible to obtain thermal ablation of the tumor region while sparing healthy tissue 3mm beyond the tumor boundary.

Finite element model to study the thermal effect of tumors in dermal regions of irregular tapered shaped human limbs

The present study deals with the temperature variation in dermal layers of irregular tapered shaped human limb involving metastasis of tumors. Two uniformly perfused tumors are assumed to be present at different axial and angular positions of the dermal regions of the human limb. The model incorporates the effect of blood mass flow rate, metabolic activity and thermal conductivity in different tissue layers. The self controlled and uncontrolled rates of metabolic heat generation are incorporated respectively for the normal and malignant tissues. Appropriate boundary conditions have been incorporated based on the physical conditions of the problem. The appropriate variations in biophysical parameters are also incorporated in the model. The finite element method has been employed for the solution. The numerical results have been used to analyze the thermal effect of metastasis of tumors on temperature distribution in dermal regions of human limbs. The thermal information generated from the numerical results can be useful for clinical applications.