Exergy destruction and entropy generation in the skeletal and cardiac muscles, lifespan entropy generation by the masseter muscles during chewing and its use as an indicator of the life expectancy

The lifespan entropy concept suggests that the organisms may have a limited capacity of lifespan entropy generation when they reach to that limit they die. The masseter muscles of a subject who is consuming food along the guide lines of Institute of Medicine (USA) may generate almost 1 x 105 J/K of entropy while chewing his food during his 76 years of expected life time. The masseter muscles of an obese person, who uptakes 10 per cent more nutrients generates the same entropy about five years earlier. The cumulative entropy generation decreases as the second law efficiency of the muscle work rises. The results of this study imply that the concept of the lifespan entropy may be correct even at the individual muscle level, and may be employed to estimate the life expectancy of a person. Experimental data from the literature are employed to carry out thermodynamic analyses of the skeletal and cardiac muscle work performance to obtain additional information beyond what the classical medical studies may offer in description of the health problems. The muscle work efficiency decreases as a result of the reduction of the metabolic energy conversion in the mitochondria with metabolic or structural failure or aging. The reduction of the mitochondrial energy generation causes further deterioration of the muscle structure, which causes in turn further decline in the muscle work efficiency. Exergy loss and entropy generation in the muscles increase as a response to the attempts to higher work production. From the thermodynamic perspective, heart can be regarded as a machine that converts part of the consumed power in external power when it pumps blood. In the course of the contraction of the heart muscle, most of the utilized chemical energy transforms into heat and a much lesser portion turns out to be work. The ratio of the work and the chemical energy expenditure is called efficiency of the cardiac contraction, or basically heart efficiency.