Thermal Modeling of the Human Eye as a Porous Structure

2009 ◽  
Author(s):  
Maryam Shafahi ◽  
Kambiz Vafai
Keyword(s):  
Blood Flow ◽  
Thermal Equilibrium ◽  
Radiation Effects ◽  
Energy Transport ◽  
Thermal Modeling ◽  
The Body ◽  
Local Thermal Equilibrium ◽  
Posterior Chamber ◽  
Convection Coefficient ◽  
Human Eye

Human eye is one of the most sensitive parts of the body when exposed to radiation effects. Since there is no barrier (such as skin) to protect the eye against the absorption of the external thermal waves, radiation can readily interact with cornea. On the other hand, lack of blood flow in the interior part of the eye makes it more vulnerable compared to other organs even in the case of weak heat interaction. Further, blood flow circulation alone cannot establish thermal equilibrium between the eye and body organs effectively. There are limitations in measuring human eye temperature profile experimentally due to the required invasive procedures in monitoring the inner layers. Therefore, there is a need to develop an accurate model to represent the eye structure and energy transport through it. Thermal modeling of the eye is important to investigate the effect of external heat sources as well as in predicting the abnormalities within the eye. Modeling of heat transport through the human eye has been the subject of interest for years, but the application of porous media models in this field is new and will be one of the themes of this study. In this work, iris/sclear is considered as a porous medium and energy transport is modeled using the tissue local thermal equilibrium equations. The eye is assumed to include six different parts: cornea, anterior chamber, posterior chamber, iris/sclera, lens and vitreous. A two-dimensional finite element simulation will be performed. Results are shown in terms of transient corneal surface temperature, isothermal lines in different regions and local temperature of pupillary axis. Effects of external radiation sources, convection coefficient of the surrounding air, blood temperature, blood convection coefficient and ambient temperature on different regions of the eye are also investigated.

Human Eye Response to Thermal Disturbances

2010 ◽  
Vol 133 (1) ◽  
Author(s):  
Maryam Shafahi ◽  
Kambiz Vafai
Keyword(s):  
Thermal Response ◽  
The Body ◽  
Posterior Chamber ◽  
Ambient Conditions ◽  
Human Eye ◽  
Blood Temperature ◽  
Element Simulation ◽  
Porous Media Model ◽  
Dimensional Finite Element

Human eye is one of the most sensitive parts of the body when exposed to a thermal heat flux. Since there is no barrier (such as skin) to protect the eye against the absorption of an external thermal wave, the external flux can readily interact with cornea. The modeling of heat transport through the human eye has been the subject of interest for years, but the application of a porous media model in this field is new. In this study, a comprehensive thermal analysis has been performed on the eye. The iris/sclera section of the eye is modeled as a porous medium. The primary sections of the eye, i.e., cornea, anterior chamber, posterior chamber, iris/sclera, lens, and vitreous are considered in our analysis utilizing a two-dimensional finite element simulation. Four different models are utilized to evaluate the eye thermal response to external and internal disturbances. Results are shown in terms of temperature profiles along the pupillary axis. Effects of extreme ambient conditions, blood temperature, blood convection coefficient, ambient temperature, sclera porosity, and perfusion rate on different regions of the eye are investigated. Furthermore, the role of primary thermal transport mechanisms on the eye subject to different conditions is analyzed.

COMPARISON OF ANTIHYPERTENSIVE EFFECT OF MOXONIDINE VERSUS CLONIDINE IN RENAL FAILURE PATIENTS.

2018 ◽  
Vol 6 (9) ◽  
Author(s):  
DR.MATHEW GEORGE ◽  
DR.LINCY JOSEPH ◽  
MRS.DEEPTHI MATHEW ◽  
ALISHA MARIA SHAJI ◽  
BIJI JOSEPH ◽  
...  
Keyword(s):  
Blood Pressure ◽  
Renal Failure ◽  
Blood Flow ◽  
Blood Vessel ◽  
Blood Vessels ◽  
High Blood Pressure ◽  
Antihypertensive Effect ◽  
The Body ◽  
Ability To Work ◽  
Blood Flows

Blood pressure is the force of blood pushing against blood vessel walls as the heart pumps out blood, and high blood pressure, also called hypertension, is an increase in the amount of force that blood places on blood vessels as it moves through the body. Factors that can increase this force include higher blood volume due to extra fluid in the blood and blood vessels that are narrow, stiff, or clogged(1). High blood pressure can damage blood vessels in the kidneys, reducing their ability to work properly. When the force of blood flow is high, blood vessels stretch so blood flows more easily. Eventually, this stretching scars and weakens blood vessels throughout the body, including those in the kidneys.

scholarly journals Calculating the optimal hematocrit under the constraint of constant cardiac power

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Michal Sitina ◽  
Heiko Stark ◽  
Stefan Schuster
Keyword(s):  
Blood Flow ◽  
High Performance ◽  
Animal Species ◽  
Normal Values ◽  
Mechanical Load ◽  
The Body ◽  
Trade Off ◽  
Cardiac Power ◽  
Optimal Value ◽  
Good Agreement

AbstractIn humans and higher animals, a trade-off between sufficiently high erythrocyte concentrations to bind oxygen and sufficiently low blood viscosity to allow rapid blood flow has been achieved during evolution. Optimal hematocrit theory has been successful in predicting hematocrit (HCT) values of about 0.3–0.5, in very good agreement with the normal values observed for humans and many animal species. However, according to those calculations, the optimal value should be independent of the mechanical load of the body. This is in contradiction to the exertional increase in HCT observed in some animals called natural blood dopers and to the illegal practice of blood boosting in high-performance sports. Here, we present a novel calculation to predict the optimal HCT value under the constraint of constant cardiac power and compare it to the optimal value obtained for constant driving pressure. We show that the optimal HCT under constant power ranges from 0.5 to 0.7, in agreement with observed values in natural blood dopers at exertion. We use this result to explain the tendency to better exertional performance at an increased HCT.

scholarly journals Acupuncture Affects Regional Blood Flow in Various Organs

2008 ◽  
Vol 5 (2) ◽  
pp. 145-151 ◽  
Author(s):  
Sae Uchida ◽  
Harumi Hotta
Keyword(s):  
Blood Flow ◽  
Cerebral Blood Flow ◽  
The Body ◽  
Neural Mechanisms ◽  
Uterine Blood Flow ◽  
Afferent Pathway ◽  
Antidromic Activation ◽  
Efferent Nerve ◽  
Afferent Nerves ◽  
Cortical Cerebral Blood Flow

In this review, our recent studies using anesthetized animals concerning the neural mechanisms of vasodilative effect of acupuncture-like stimulation in various organs are briefly summarized. Responses of cortical cerebral blood flow and uterine blood flow are characterized as non-segmental and segmental reflexes. Among acupuncture-like stimuli delivered to five different segmental areas of the body; afferent inputs to the brain stem (face) and to the spinal cord at the cervical (forepaw), thoracic (chest or abdomen), lumbar (hindpaw) and sacral (perineum) levels, cortical cerebral blood flow was increased by stimuli to face, forepaw and hindpaw. The afferent pathway of the responses is composed of somatic groups III and IV afferent nerves and whose efferent nerve pathway includes intrinsic cholinergic vasodilators originating in the basal forebrain. Uterine blood flow was increased by cutaneous stimulation of the hindpaw and perineal area, with perineal predominance. The afferent pathway of the response is composed of somatic group II, III and IV afferent nerves and the efferent nerve pathway includes the pelvic parasympathetic cholinergic vasodilator nerves. Furthermore, we briefly summarize vasodilative regulation of skeletal muscle blood flow via a calcitonin gene-related peptide (CGRP) induced by antidromic activation of group IV somatic afferent nerves. These findings in healthy but anesthetized animals may be applicable to understanding the neural mechanisms improving blood flow in various organs following clinical acupuncture.

scholarly journals Chinese Herbal Medicine Alleviates Thyroidectomy-Induced Cardiopulmonary Exercise Dysfunction in Rats

2020 ◽  
Vol 2020 ◽  
pp. 1-8 ◽  
Author(s):  
Tai-Yuan Chuang ◽  
Chia-Ying Lien ◽  
Chih-Hsiang Hsu ◽  
Chen-Wen Lu ◽  
Chung-Hsin Wu
Keyword(s):  
Blood Flow ◽  
Body Weight ◽  
Negative Control ◽  
The Body ◽  
Male Rats ◽  
Free Triiodothyronine ◽  
Cardiopulmonary Exercise ◽  
Chinese Herbal ◽  
Subcutaneous Blood Flow ◽  
Tsh Levels

Hypothyroidism frequently causes cardiopulmonary dysfunction, such as heart failure and respiratory and metabolic deficiencies. This study investigated the effects of Chinese herbal formula B307 on thyroidectomy-induced cardiopulmonary exercise dysfunction in rats. Twenty male rats were equally divided into four groups: negative control with sham treatment, positive control with oral B307 treatment only, thyroidectomy treatment only, and thyroidectomy with B307 posttreatment groups. The feeding dose of B307 was 50 mg/kg per day for 14 days. We examined and then compared the thyroid-stimulating hormone (TSH), free triiodothyronine (T3), free thyroxine (T4), and reactive oxygen species (ROS) from the blood of these four groups. Also, we compared the body weight, neck subcutaneous blood flow, cardiac ejection function, cardiopulmonary exercise function of oxygen consumption (VO2), carbon dioxide production (VCO2), and respiratory quotient (RQ = VCO2/VO2) among the four groups. Our results indicated that thyroidectomized rats had significantly decreased body weight, neck subcutaneous blood flow, cardiac ejection function, serum T3 and T4, and VO2 and VCO2, but had significantly increased ROS and TSH levels and RQ values compared with sham rats (P<0.01–0.05). In addition, thyroidectomized rats receiving oral B307 treatment had significantly increased body weight, neck subcutaneous blood flow, cardiac ejection function, and VO2, but significantly decreased ROS and TSH levels and VCO2 and RQ values compared with thyroidectomized rats (P<0.01–0.05). We suggest that the B307 could be a protective and beneficial alternative treatment for thyroidectomy-induced cardiopulmonary exercise dysfunction.

Regional blood flow measurement in vivo for a definable geometry

1964 ◽  
Vol 206 (5) ◽  
pp. 962-966 ◽  
Author(s):  
Marvin B. Bacaner ◽  
James S. Beck
Keyword(s):  
Blood Flow ◽  
Flow Measurement ◽  
Necessary Conditions ◽  
Regional Blood Flow ◽  
The Body ◽  
Continuous Measure ◽  
Radioisotope Method ◽  
Arterial Concentration ◽  
Regional Concentration

A radioisotope method for measuring regional blood flow in the intestine of the dog in vivo has been favorably compared with measurement by timed collection of total venous outflow. The necessary conditions are a continuous measure of arterial concentration and cumulative regional concentration of radioisotope, an experimentally definable region, and temporary complete retention of tracer. The derivation of the relations used suggests additional applications of the method to other regions of the body.

A NUMERICAL STUDY ON THE HEMODYNAMIC AND SHEAR STRESS OF DOUBLE ANEURYSM THROUGH S-SHAPED VESSEL

2015 ◽  
Vol 27 (04) ◽  
pp. 1550033 ◽  
Author(s):  
Mahdi Halabian ◽  
Alireza Karimi ◽  
Borhan Beigzadeh ◽  
Mahdi Navidbakhsh
Keyword(s):  
Blood Flow ◽  
Mechanical Behavior ◽  
Numerical Study ◽  
Flow Characteristics ◽  
Flow Simulation ◽  
The Body ◽  
Sweep Angle ◽  
Abdominal Aortic ◽  
Hemodynamic Characteristics ◽  
Refined Meshes

Abdominal aortic aneurysm (AAA) is a degenerative disease defined as the abnormal ballooning of the abdominal aorta (AA) wall which is usually caused by atherosclerosis. The aneurysm grows larger and eventually ruptures if it is not diagnosed and treated. Aneurysms occur mostly in the aorta, the main artery of the chest and abdomen. The aorta carries blood flow from the heart to all parts of the body, including the vital organs, the legs, and feet. The objective of the present study is to investigate the combined effects of aneurysm and curvature on flow characteristics in S-shaped bends with sweep angle of 90° at Reynolds number of 900. The fluid mechanics of blood flow in a curved artery with abnormal aortic is studied through a mathematical analysis and employing Cosmos flow simulation. Blood is modeled as an incompressible non-Newtonian fluid and the flow is assumed to be steady and laminar. Hemodynamic characteristics are analyzed. Grid independence is tested on three successively refined meshes. It is observed that the abrupt expansion induced by AAA results in an immensely disturbed regime. The results may have implications not only for understanding the mechanical behavior of the blood flow inside an aneurysm artery but also for investigating the mechanical behavior of the blood flow in different arterial diseases, such as atherosclerosis.

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