The exergy analysis of the human body is a tool that can provide indicators of health and life quality. To perform the exergy balance it is necessary to calculate the metabolism on an exergy basis, or metabolic exergy, although there is not yet consensus in its calculation procedure. Hence, the aim of this work is to provide a general method to evaluate this physical quantity for human body based on indirect calorimetry data. To calculate the metabolism on an exergy basis it is necessary to define the reference reactions and obtain their exergy variation. The reference reactions of the energy substrates are represented by the oxidation of the glucose, palmitic acid and a representative amino acid. Hence, from the exergy variation of these reactions and the consumption rate of the substrates, the metabolic exergy is determined. Results, for basal conditions and during physical activities, indicate that the difference between exergy and energy metabolisms is lower than 5%. Moreover, the body converts approximately 60% of the exergy of nutrients into available exergy to perform work.Keywords: Human Body; exergy analysis; metabolic exergy. IntroductionThe application of the exergy analysis to the human body may be used to assess the quality of the energy conversion processes that take place in its several systems, organs and even cells. Several authors applied the analysis for the human body and some of the methods were revised by Mady et al., (2012). To perform the exergy analysis it is necessary to calculate the metabolic exergy of the human body, but there is not yet a consensus in its calculation.Initially, the second law of thermodynamics was applied to living organisms as an attempt to confirm the principle of minimum entropy production or Prigogine & Wiame (1946) principle. In this principle it is stated that all living organisms tend to a minimum of entropy production. Therefore, Zotin & Zotina (1967), Balmer (1984, Aoki (1991), Silva & Annamalai (2008) and Mady et al. (2012 confirmed the principle of minimum entropy production for different types of species, ranging from fish to humans. Batato et al. (1990) were one of the first authors that applied the exergy analysis to the human body. In their analysis the energy and exergy metabolism were calculated from indirect calorimetry results, where representative reactions of oxidation of three types of substance (carbohydrates, lipids and proteins) were selected. A comparison between metabolisms in both basis indicates that the difference is not higher than 5%.Prek (2005, 2006), Prek and Butala (2010) and Simone et al. (2011) performed the exergy analysis for the human body to obtain relations between the destroyed exergy and thermal comfort and thermal sensation conditions. In their analyses the metabolic exergy was considered as a heat source, therefore the metabolism on energy and exergy basis have one order of magnitude of difference.

No abstract

No abstract

Cardiac interstitial fibrosis may contribute to ventricular dysfunction and the prognosis of patients with dilated cardiomyopathy. The objective of the present study was to determine if total myocardial collagen content and collagen type III/I (III/I ratio) mRNAs differ in hypertensive, alcoholic, and idiopathic dilated cardiomyopathy subjects. Echocardiography and exercise cardiopulmonary testing were performed in patients with idiopathic (N = 22), hypertensive (N = 12), and alcoholic (N = 11) dilated cardiomyopathy. Morphometric analysis of collagen was performed in fragments obtained by endomyocardial biopsy with picrosirius red staining. The collagen III/I ratio was determined by reverse transcription polymerase chain reaction. Samples of controls (N = 10) were obtained from autopsy. Echocardiographic variables and maximal oxygen uptake were not different among dilated cardiomyopathy groups. Collagen was higher in all dilated cardiomyopathy groups (idiopathic, hypertensive and alcoholic, , , , , 7.36 ± 1.09%) versus controls (1.12 ± 0.18%), P < 0.05. Collagen was lower in idiopathic dilated cardiomyopathy (4.97 ± 0.83%) than hypertensive (8.50 ± 1.11%) and alcoholic (10.77 ± 2.09%) samples (P < 0.005 for both). The collagen III/I ratio in all samples from dilated cardiomyopathy patients was higher compared to that in controls (0.29 ± 0.04, P < 0.05) but was the same in the samples from idiopathic (0.77 ± 0.07), hypertensive (0.75 ± 0.07), and alcoholic (0.81 ± 0.16) dilated cardiomyopathy groups. Because of the different physical properties of the types of collagen, the higher III/I ratio may contribute to progressive ventricular dilation and dysfunction in dilated cardiomyopathy patients.

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, body 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: respiratory system and human body as a whole. Data concerning mass and energy balances of the body and respiratory system were obtained from models available in the literature, which were modified based on medical literature to simulate the responses to physical activity at high altitude for different periods of acclimatization. The results indicated that the respiratory system exergy efficiency is reduced at high altitudes and under physical activity, while exergy efficiency of the body increases for both parameters, which may indicate that the discomfort reported at high altitudes is mostly related to the respiratory system than to the other ones. Concerning the acclimatization period, its influence was more pronounced on the respiratory system.

No abstract

Abstract:The first and second laws of thermodynamics were applied to the human body in order to evaluate the quality of the energy conversion during muscle activity. Such an implementation represents an important issue in the exergy analysis of the body, because there is a difficulty in the literature in evaluating the performed power in some activities. Hence, to have the performed work as an input in the exergy model, two types of exercises were evaluated: weight lifting and aerobic exercise on a stationary bicycle. To this aim, we performed a study of the aerobic and anaerobic reactions in the muscle cells, aiming at predicting the metabolic efficiency and muscle efficiency during exercises. Physiological data such as oxygen consumption, carbon dioxide production, skin and internal temperatures and performed power were measured. Results indicated that the exergy efficiency was around 4% in the weight lifting, whereas it could reach values as high as 30% for aerobic exercises. It has been shown that the stationary bicycle is a more adequate test for first correlations between exergy and performance indices.

The present work evaluates the impact of carbon monoxide (CO) inhalation on the human lung’s exergy behavior by considering different levels of intoxication and amounts of hemoglobin. Its impact is significant because CO is one of the most common air pollutants in cities and an increase in destroyed exergy may be correlated with lifespan reduction or the malfunctioning of certain human organs. An evaluation of the severity of intoxication as a function of city altitude may intensify the hazard associated with carbon monoxide. A computational model of human lungs obtained from the literature was used to calculate the concentrations of oxygen (O2), carbon monoxide (CO), and carbon dioxide (CO2) in the respiratory system. With the purpose of better evaluating the different levels of CO intoxication and hemoglobin concentration (which is a function of acclimatization time and some pathologies, such as anemia), a model calculating exergy efficiency for the lungs was proposed. From this model, it was possible to conclude that a higher level of intoxication is associated with lower exergy efficiency values. When associated with carbon monoxide intoxication, higher hemoglobin levels also result in lower efficiency. Eventually, a comparison between previous studies and the current study was carried out, regarding the method employed to calculate the exergy destroyed in the lungs, considering not only gas transport, but also hemoglobin concentration and its reaction with the gases from a second law perspective.