SpecialityUniversity of North Texas, USA

Stress, Hemoglobin, and Criticality. A non-equilibrium thermodynamics perspective.All living organisms are complex adaptive systems and exchange energy and entropy with their environment as open thermodynamic systems. Chemical reactions on which living organisms depend may be complex but are not considered adaptive and are closed thermodynamic systems. Termed “dissipative structures” by the Nobel Laureate Ilya Prigogine, living organisms dissipate matter and energy to maintain organization and structure and are in a state of non-equilibrium, while chemical reactions often reach equilibrium. Exposed to stressors, such as increased environmental temperature or hypoxia, all living organisms undergo a back-and-forth pattern of self-regulation (allostasis – stability through change) and dysregulation (or metastasis - instability through change or the process underlying dysregulation). But if exchange rates of energy/entropy exceed dissipation rates, overload, and dysregulation can result in death or, in adaptive systems, may undergo a state change. These responses to stressors reflect different inherent patterns of complexity (e.g., non-crucial vs crucial events), but it is crucial events determining the efficiency of information transfer, especially during key state changes. Chemical molecules such as hemoglobin (Hb), an iron-containing oxygen transport protein in the blood, also undergo reversible and functional state changes when reacting with environmental stressors, such as hypoxia. But mutant HbS causing sickle cell disease in humans when exposed to hypoxia forms reversible, non-functional deoxy-paracrystalline arrays unable to carry oxygen around the body thus, fostering disease (dysregulation). Therefore, it is unclear if changes in complexity patterns, (non-crucial vs crucial events), also accompany state changes in chemical reactions or whether they are found only in living organisms.