Thermodynamic effect of RNA virus infection on the human cardiovascular system.

In this work, analysis of cardiovascular system under the influence of RNA virus infection has been performed from a thermodynamic perspective. An exergetic efficiency of the system has been defined for this purpose. Results show that except for asymptomatic case, the exergetic efficiency reduces as the viral load goes up. Dynamics of viral growth along with change in efficiency is examined under different parameters such as virus production rate, infectivity rate and cell death rate. Results show that the drop in the exergetic efficiency of cardiovascular system under viral infection can be up to about 20%. Under infection, the exergy requirement of the lungs increases significantly as the work rate required by lungs increase by up to 240%.

A Brief on Biological Thermodynamics for Human Physiology.

Thermodynamics, the science of energy interactions, governs the direction of processes found in nature. While the subject finds wide applications in science and technology, its connection to biological sciences and in particular to bio-engineering is becoming increasingly important. In this work, after a brief introduction to the fundamental concepts in thermodynamics, we focus on its application in human physiology. A review of application of thermodynamics to the interaction between human body and environment is presented. Research works on biological systems such as the nervous system and the cardiovascular systems are summarized. The thermodynamics of metabolism is reviewed, and finally, the role of the subject in understanding and combating diseases is highlighted.

Performance analysis of human respiratory system based on the second law of thermodynamics.

The purpose of this study is to develop a comprehensive thermodynamic model of the human respiratory system and quantify the effects of inspiratory air temperature, relative humidity (RH), lung capacity and O2 fluctuation in metabolic reaction on the human respiratory system under three different physiological conditions, i.e. rest, moderate level of physical activity and extreme level of physical activity. Therefore, a second law-based analysis has carried out for the human respiratory system. It is observed that exergetic efficiency decreases by 21% and 16.5% during moderate and extreme level of activity respectively as compared to the physical condition of rest. The respiratory efficiency also increases with the increase in inspiratory air temperature and RH. For a given inspiratory air temperature, an increase in lung volume leads to a reduction in the efficiency. Increase in TV with a high airflow rate gives a higher magnitude of efficiency, such a situation appearing when a person's lung compliance harmed due to diseases. The respiratory efficiency decreases up to 2% with the increase in O2 percentage. The efficiency of the respiratory system is in maximum during rest followed by an extreme and moderate level of activity. However, with the controlled supply of O2, the efficiency of the human respiratory performance increases with the decrease in O2 percentage. Due to partial oxidation of glucose at a reduced O2 level, exergy input from the metabolic reaction is less leading to increased exergetic efficiency.

Three dimensional numerical analysis of hemodynamic of stenosed artery considering realistic outlet boundary conditions.

BACKGROUND AND OBJECTIVE: Mortality rate increases globally among which one third is due to diseased blood vessels. Due to late diagnoses of the disease in vessels (severe stenoses), qualitative and rapid assessment becomes difficult. Earlier assessment of stenoses can lead to formulation of effective treatment protocol. It is often found that proliferation of secondary stenoses at downstream of a stenosed vessel depends on the degree of severity of primary stenoses. Numerical investigation of flow dynamics of blood in such condition helps in prediction of distributed field of secondarystenoses. This investigation also requires consideration of rigorous boundary conditions at inlet and outlet of defined flow domain. METHODS: Patient-specific geometry of aortic arch with stenoses in descending aorta was considered for numerical estimation of biofluid dynamics. Boundary conditionsat inlet and outlet were extracted from time-resolved pulsed Doppler Ultrasound imaging at appropriate sections of the vessel. Womersley inlet flux was considered. Flow parameters like wall shear stress, oscillatory shear index, etc. were evaluated at upper and lower aortic arch of the vessel at different combinations of boundary conditions at inlet and four outlets respectively. RESULTS: Effect of outlet boundary conditions were acknowledged for the progression of secondary stenoses. Severity of primary stenoses was found influencing the progression of secondary stenoses. It was found that the outlets Left Subclavian Artery and Left Common Carotid Artery greatly influence the flow dynamic structure within the stenosed aortic arch. Simultaneously, lower wall of aortic-arch had shown more affinity for secondary stenoses progression. CONCLUSION: Aortic arch is a vital anatomical region of circulatory system which is vulnerable to progression of secondary stenoses in presence of primary stenoses in ascending or descending aorta. It also drives the author to speculate the influence of anurysm in descending aorta on this landmark of aortic arch.

Entropy generation in the human lung due to effect of psychrometric condition and friction in the respiratory tract.

BACKGROUND AND OBJECTIVE: Entropy generation is associated with the irreversibility of any thermodynamic system. It provides an indication of lost energy and hence the efficiency of a system. In this paper, an attempt has been made to study the effects of specific humidity, relative humidity, ambient temperature change, breathing air friction with the respiratory tract on the entropy generation during the respiration process at different physiological conditions. METHODS: To address the above issues, a human respiratory tract model with realistic length to diameter ratio at different branches has been considered. The analysis examines air flow rates of 6 lpm and 60 lpm during rest and exercise condition respectively; corresponding to breathing rates of 30 and 60 per minute, respectively. The body temperature has been considered at 36°C, and ambient condition of air has been taken at 25°C DBT and 50% RH. The respiratory tract geometry has been modelled on the basis of Weibel's experimental results. RESULTS: It has been noticed that, at a particular Lewis number entropy generation per day decreases with the increase in specific humidity, again at a particular specific humidity entropy generation increases with the decrease in Lewis number. For a particular physical condition and Lewis number entropy generation decreases with the increase in relative humidity. In this work, it has been observed that negentropy increases with the increase in ambient temperature for a constant relative humidity, however the net entropy generation is always positive. This study reports that, maximum resistance of flow occurs where duct aspect ratio (i.e. tract diameter to length) is minimal. For a typical geometry of air passage, velocity of flow increases up to 3rd generation then it is decreases gradually till 23rd generation. Amount of entropy generation goes on reducing as the duct goes on bifurcating except for the third generation where a local peak in entropy generation is observed. This is a consequence of typical geometry of human respiratory duct. This work reveals that, at rest entropy generation due to conditioning of breathing air is higher than its frictional component and during heavy physical activity, entropy generation due to breathing air friction with the respiratory tract is higher than its air conditioning component. CONCLUSIONS: Entropy generation is significantly higher due to conditioning of breathing air than that of frictional effect with the tract. This is a preliminary attempt in quantifying this aspect and the authors believe that, these two components of entropy generation have a probable connection with the bronchial thermoplasty, which helps to treat the asthma.

Assessment of Influences of Stenoses in Right Carotid Artery on Left Carotid Artery Using Wall Stress Marker.

Purpose. Atherosclerosis is a diseased condition of blood vessel. It causes partial blockage in lumen of vessel and affects hemodynamic of localized flowing blood. Complex geometries like region of bifurcation also affects hemodynamic to a larger extent. Complexity further increases in presence of stenoses at region of bifurcation. Such morphological change in vessel largely affects parent as well as corresponding sister and daughter vessels. In this paper, complexity in hemodynamic of blood in pair of carotid arteries (left and right carotid arteries) is evaluated in presence of stenoses at basilar segment of right artery in three-dimensional domain using reconstructed tomographic images of patient. Methods. Transient information of blood flow is obtained using four-dimensional phase-contrast MRI technique. Haematocrit component of blood at diseased condition is considered using Power Law and Quemada model. Numerical techniques are used to solve pressure-coupled governing equations of flowing blood. Results. Dysfunctions of endothelial cells near the wall are characterised by evaluating shear stress markers. Wall shear stress and its gradient based and harmonic based descriptors are calculated over complete geometry during one cardiac cycle. Conclusion. Internal branch of left carotid artery and external branch of right carotid artery are found prone to secondary stenoses in presence of primary stenoses at basilar segment of right carotid artery.

Numerical investigations of pulsatile flow in stenosed artery.

PURPOSE: Abnormalities in blood vessels by virtue of complex blood flow dynamics is being supported by non-Newtonian behavior of blood. Thus it becomes a focus of research to most of the researchers. Additionally, consideration of real life patient specific model of vessel as well as patient specific inlet flow boundary condition implementation was limited in literature. Thus a thorough implementation of these considerations was done here. METHOD: In this work, a numerical investigation of hemodynamic flow in stenosed artery has been carried out with realistic pulsating profile at the inlet. Flow has been considered to be laminar due to arresting condition of cardiovascular state of the subject. Two non- Newtonian rheological models namely, Power Law viscosity model and Quemada viscosity model have been used. Two different patient- specific pulsatile profiles are considered at the inlet of a long stenosed artery with varying degree of stenoses from 25% to 80%. RESULTS: Transient form of Navier-Stokes equation is solved in an axi-symmetric domain to calculate the detailed flow structure of the flow field. From the simulation data, temporal and time averaged wall shear stress, oscillatory shear index and pressure drop are calculated. CONCLUSIONS: The results demonstrate that oscillatory shear index and wall shear stresses are extensively governed by the degree of stenoses. The position and movement of recirculation bubbles are found to vary with flow Reynolds number.