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The effect of altitude and intensity of physical activity on the exergy efficiency of respiratory system
(2013-07-16) HENRIQUES, I. B.; Carlos Mady; Cyro Albuquerque; YANAGIHARA, J. I.; OLIVEIRA JUNIOR, S.
The effect of altitude on exercise performance of lowlanders has long been discussed, but it is still unclear whether the performance reduction is related to inefficiency of the respiratory system, tissues or both. In the present work, exergy analysis was applied to the human body in order to compare its exergy efficiency under basal conditions and during physical activity at sea level and high altitudes for different periods of acclimatization. Two control volumes were analyzed: the respiratory system, which comprises the lungs and the airways, and the human body as a whole. In the first control volume, the exergy rates and flow rates are associated with the venous blood and the inspired air in the inlet and the arterial blood and expired air in the outlet. An internal exergy variation due to the exergy metabolism of the lung, an exergy transfer rate associated with the metabolism of the lung and the power performed by the respiratory muscles were also taken into account. Analyzing the second control volume, the exergy transferred rate to the environment due to the heat losses by convection and radiation were considered, as well as the exergy flow rate associated with respiration and transpiration. The temperatures of different parts of the body and the heat losses to the environment were obtained from a heat transfer model of the human body. The data concerning gas and blood flows were obtained from a model of the respiratory system. The last one was modified based on medical literature to simulate the response to physical activity at high altitude for different periods of acclimatization, from the first moment that the body is exposed to a high altitude environment to three months of acclimatization. The results obtained indicated that the respiratory system exergy efficiency is reduced at high altitudes and under physical activity, while the exergy efficiency of the body increases for both parameters. Concerning the acclimatization period, its influence was more pronounced in the respiratory system. It was possible to observe a decrease in the exergy efficiency of the respiratory system in the first two days. From this moment on, the efficiency increased continuously until the twentieth day, when it is stabilized and remains constant.
The effect of carbon monoxide in the exergy behavior of lungs
(2017-07-02) CENZI, J. R.; HENRIQUES, I. B.; Cyro Albuquerque; YANAGIHARA, J. I.; OLIVEIRA, S.; Carlos Mady
© 2017 IMEKOThe present work evaluates the impact of carbon monoxide inhalation in the human lungs exergy behaviour for different levels of intoxications and altitude. It is significant because this substance is one of the most common air pollutants in cities and an increasing in the destroyed exergy can be associated with a reduction in lifespan. Moreover, an evaluation of the severity as a function of the city height may intensify the hazard associated with carbon monoxide. In order to evaluate these consequences, a carbon monoxide transportation model obtained in literature was used to calculate the concentrations of oxygen, carbon monoxide and carbon dioxide in the different respiratory system tissues. With the purpose to better evaluate the different levels of carbon monoxide intoxication and hemoglobin concentration (which is a function of acclimatization time) it was proposed an exergy efficiency for the lungs. From this model, it was possible to conclude that a higher level of intoxication is associated to lower exergy efficiency values. Higher hemoglobin levels when associated to carbon monoxide intoxication also results in lower efficiencies.
An integrated model of the thermoregulatory and respiratory systems of the human body
(2020-07-05) YANAGIHARA, J. I.
© 2020 Elsevier LtdThis work aims to develop a mathematical model for computing the distribution of temperature, O2, and CO2 in the human body, depending on the ambient conditions. The body is divided into segments, including layers of tissues and blood compartments, where mass and energy balances are applied. The inclusion of O2 and CO2 transfer mechanisms throughout all segments and tissues of the human body is one of the great novelties of this work. It also includes the exothermic metabolic reactions in the tissues, the transportation of O2 and CO2 by the blood, and the energy exchanged with the environment through the skin and by ventilation. The model also includes the regulation of metabolism, circulation, ventilation, and sweating, depending on the body temperature and the concentrations of O2 and CO2 in the blood. The lungs are represented by alveolar and blood compartments, with diffusion between them. Comparisons with experimental data from the existing literature show that the proposed model is suitable for representing transient exposure to cold and warm ambient temperatures, low concentration of O2, and high concentrations of CO2. In the end, some results demonstrate the effect of ambient temperature on the distribution of temperature, O2, and CO2 across segments, blood, and tissues. Shivering in a cold environment reduces the concentration of O2 and increases the concentration of CO2 in the muscles, which results in increased ventilation and blood circulation. The concentration of gases in the skin depends mainly on variations in the skin's circulation with the environment, which alters the availability of O2 and the elimination of CO2. Small variations were found in the concentrations of O2 and CO2 in the brain and lungs.

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