Exergy based indicators for cardiopulmonary exercise test evaluation

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Mady C.E.K.
Albuquerque-Neto C.
Fernandes T.L.
Hernandez A.J.
Saldiva P.H.N.
Yanagihara J.I.
Junior S.D.O.
Proceedings of the 25th International Conference on Efficiency, Cost, Optimization and Simulation of Energy Conversion Systems and Processes, ECOS 2012
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The cardiopulmonary exercise test is one of the most used tests to assess the functional capacity of individuals with varying degrees of physical training. One of the indices that are used for these analyses is the maximum oxygen consumption (maximum capacity of the body to transfer and transport oxygen to tissues). Lactate threshold is another metabolic parameter used to identify the state of the aerobic training. During the experimental procedure, the individuals are submitted to increasing levels of velocities, which is suitable for the obtainment of the blood lactate concentration. The aim of this work is the development of performance indicators for individuals under physical activity based on the concepts of exergy destroyed rate and exergy efficiency. To perform the exergy analysis, it was necessary to calculate heat and mass flow rates, associated with radiation, convection, vaporization and respiration, determined from the measurements and some relations found in the literature. The energy balance allowed the determination of the internal temperature over time. Those information were used to obtain the exergy variation of the body along the experiment. Eventually, it was possible to calculate the destroyed exergy and the exergy efficiency from the exergy analysis. During the tests the following measurements were made: the skin temperature of the trunk, legs and arms, the tympanic temperature, the respiratory gas exchanges, the blood lactate concentration, and some anthropometric parameters. The exergy rates and flow rates are dependent of the exercise level and the body metabolism. The results show that the relation between the destroyed exergy and the metabolism is almost constant during the test; furthermore its value has a great dependence of the subject age. Moreover, the exergy efficiency has a different behavior between the low trained subjects and the others.