Performance analysis of human cardiorespiratory system based on the second law of thermodynamics

This work presents a thermodynamic model of the human cardiorespiratory system under different physiological conditions based on the second law of thermodynamics. The analysis reports three different physiological conditions i.e., rest, moderate level of physical activity and extreme level of physical activity. Human cardiorespiratory performance is found to increase significantly with the increase in physical activity. However, the cardiorespiratory performance also notably increases with the increase in ambient temperature and RH. The cardiomegaly condition of the cardiorespiratory system decreases the efficiency of the system. Results show that O2 fluctuation for metabolic use has no significant effect on the human cardiorespiratory performance. A new dimensionless number, which is the ratio of breathing rate to the heart rate (BHR), is introduced in this work. The present work reveals that the thermodynamic performance of the cardiorespiratory system depends on the inhaled air property (temperature and RH), cardiomegaly condition and the variation of BHR.