A Stoichiometric Model of Human Metabolism

The present study deals with the “Human” component of the bioregenerative life support system. Here we develop a model that allows calculating metabolic mass flow rates of the “Human” component and monitoring the production of toxic substances – ammonia, hydrogen sulfide, and methanethiol. The model is designed as an Excel-VBA interactive program. The “Human” component is considered as an object with incoming and outgoing flows of matter. Food ingredients, water, and oxygen constitute the input flows, and the outgoing flows consist of metabolic products. The input flows are distributed along metabolic channels. To specify the characteristics of the “Human” component, a calorie counter and a space diet planner are connected to the model. The calorie counter is designed to determine a crewman’s daily energy requirements depending on age, weight, height, gender, and level of physical activity. In turn, the numerical energy value is transmitted to the diet planner, which determines the food set. To more accurately present the metabolism of phosphorus, nucleic acids and phospholipids are included in the food composition. Each substance in the model is assigned a stoichiometric formula. The core of the model consists of seven stoichiometric equations and the water exchange unit, which are the link between the incoming and outgoing flows of matter. The solution of stoichiometric equations and balancing the water exchange unit are carried out using the Solver Add-in for Excel, which is embedded in the metabolic circuit. To show the validity of the model, a calculation of the human metabolism depending on calorie counter and diet planner is presented.