Far-from-equilibrium thermodynamics of the human uterus: A self-organized dissipative structure.

The aim of this study was to know how the human uterine muscle behaves from a thermodynamic point of view in pregnant and non-pregnant states. According to far-from-equilibrium thermodynamics, an open system is far-from-equilibrium when its thermodynamic force varies non-linearly with its thermodynamic flow. These two quantities can be calculated on muscles and therefore on the uterine muscle, using the Huxley formalism. The thermodynamic flow was greater in non-pregnant compared to pregnant uterine muscle, while the thermodynamic force was equal in both cases. There was a linear relationship between these two quantities in pregnant uterine muscle, whereas a non-linear relationship characterized the non-pregnant state. Thus, the non-pregnant uterine muscle worked far-from-equilibrium. The product of thermodynamic force and thermodynamic flow was the energy production rate (EPR). EPR was much greater in pregnant uterine muscle. The derivative with respect to time of EPR was called excess entropy production (EEP). EEP was positive in the pregnant state and negative in the non-pregnant state. A first-order nonlinear differential equation with one parameter demonstrated a bifurcation. These results showed that the non-pregnant uterine muscle was a self-organized far-from-equilibrium dissipative structure.