AbstractIn this paper we report on the development of a dynamic MATLAB SIMULINK® model for the water and electrolyte balance inside the human body. This model is part of an environmentally sensitive dynamic human model for the optimization and verification of environmental control and life support systems (ECLSS) in space flight applications.An ECLSS provides all vital supplies for supporting human life on board a spacecraft. As human space flight today focuses on medium- to long-term missions, the strategy in ECLSS is shifting to closed loop systems. For these systems the dynamic stability and function over long duration are essential. However, the only evaluation and rating methods for ECLSS up to now are either expensive trial and error breadboarding strategies or static and semi-dynamic simulations. In order to overcome this mismatch the Exploration Group at Technische Universität München (TUM) is developing a dynamic environmental simulation, the “Virtual Habitat” (V-HAB). The central element of this simulation is the dynamic and environmentally sensitive human model. The water subsystem simulation of the human model discussed in this paper is of vital importance for the efficiency of possible ECLSS optimizations, as an over- or under-scaled water subsystem would have an adverse effect on the overall mass budget. On the other hand water has a pivotal role in the human organism.Water accounts for about 60% of the total body mass and is educt and product of numerous metabolic reactions. It is a transport medium for solutes and, due to its high evaporation enthalpy, provides the most potent medium for heat load dissipation.In a system engineering approach the human water balance was worked out by simulating the human body’s subsystems and their interactions. The body fluids were assumed to reside in three compartments: blood plasma, interstitial fluid and intracellular fluid. In addition, the active and passive transport of water and solutes between those compartments was modeled dynamically. A kidney model regulates the electrolyte concentration in body fluids (osmolality) in narrow confines and a thirst mechanism models the urge to ingest water. A controlled exchange of water and electrolytes with other human subsystems, as well as with the environment, is implemented. Finally, the changes in body composition due to muscle growth are accounted for. The outcome of this is a dynamic water and electrolyte balance, which is capable of representing body reactions like thirst and headaches, as well as heat stroke and collapse, as a response to its work load and environment.
A dynamic human water and electrolyte balance model for verification and optimization of life support systems in space flight applications
Acta Astronautica ; 67 , 9-10 ; 1003-1024
2010-06-01
22 pages
Article (Journal)
Electronic Resource
English
Life support systems , Dynamic simulation , Virtual habitat , Human modeling , Water balance simulation , Human physiology simulation , ADH , Antidiuretic hormone , ALD , Aldosteron , AngII , Angiotensin II , BP , Blood plasma , BWL , Body water loss , ECLSS , Environmental control live support system , ESM , Equivalent system mass , GTB , Glomerular-tubular balance , ICF , Intracellular fluid , INT , Interstitial fluid , MCL , Model confidence level , TRL , Technology readiness level , V-HAB , <italic>c</italic><inf>ADH</inf> , Concentration of ADH , <italic>Fl</italic><inf>sw</inf> , Actual sweat flow , <italic>Fl</italic><inf>sw,dem</inf> , Demanded sweat flow , <italic>p</italic><inf>env</inf> , Environmental pressure , <italic>R</italic><inf>per,act</inf> , Actual peripheral resistance , <italic>R</italic><inf>per,0</inf> , Basal peripheral resistance , <italic>T</italic><inf>env</inf> , Environmental temperature , <italic>φ</italic> , Relative air moisture
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