Thermodynamic analysis of human respiratory (diaphragm) skeletal muscles

Introduction: From the thermodynamic perspective, the diaphragm is an open thermal system and can be regarded as a machine (piston) that converts part of the consumed power in external power during a breathing cycle. Aims and objectives: Aim of the study is to determine the exergy destruction and entropy generation by using thermodynamic analysis of the work done in the diaphragm muscle. Methods: In this study, a human respiratory system was modeled as the diaphragm skeletal muscle. Then, the first and second laws of thermodynamics were utilized to analyze these systems. Mass, energy, exergy and entropy balances are performed around the diaphragm muscles to calculate the glucose consumption, exergy destruction and entropy generation. Results: As a result of the thermodynamic analysis of the work for resting state respiration (diaphragm) performed by a healthy adult individual, the minimum and maximum values of the exergy destruction were calculated to change from 8.41x10^-3 kJ/min to 12x10^-3 kJ/min, respectively. Entropy generation was found to be between 2.82x10^-5 and 4.03x10^-5. The glucose used by the diaphragm muscle is calculated for minimum and maximum work values. Given the results of the energy balance analysis according to the first law of thermodynamics, the glucose consumed for this work was calculated as 0.22-0.31 mmol/min. Conclusions: When the muscle work done by the diaphragm is maximized, exergy destruction is also increasing. In individuals with Chronic Obstructive Pulmonary Disease, considering the increased muscle work to be done for respiration, entropy generation may be expected to increase further in these patients.