A quantitative estimation of regulation and transport limitations in the human cardiopulmonary system

The object of this dissertation is to quantitatively describe the regulation of some of the exchange processes within the human body. Conceptually this dissertation is divided into two sections. In the first section a macroscopic view was adopted to describe the overall regulation of the cardiovascular and respiratory systems. These overall system models were used as heuristic tools to gain an understanding of physiological behavior in micro-gravity. In the second section, a microscopic view was used to estimate the role played by the surfactant system of the lung in regulating the transfer of fluid across the pulmonary-capillary wall;The basis of the cardiovascular system model is the maintenance of arterial blood pressure homeostasis. Sub-models constituting the overall model are: the pressure-flow model, the heart action model, the controller model which describes short term-control, and the renal model which describes long term control and the regulation of total body water content. Model predictions show that incorporating the fluid shift from the lower to the upper part of the body in micro-gravity is sufficient to account for the cardiovascular changes occurring in micro-gravity;The respiratory model is concerned with the maintenance of a constant carbon dioxide level in the tissue and body fluids. The sub-models constituting the overall respiratory model are: the gas-exchange model, the mechanics model, and the controller model which determines the ventilation and cardiac output on the basis of arterial blood gas tensions. Simulation results show that pleural pressure homogeneity, increased lung diffusing capacity and decreased lung volume are sufficient to describe respiratory changes in micro-gravity;In the penultimate section the lung mechanics model is coupled with a model of fluid exchange across the pulmonary-capillary wall. The lung mechanics model estimates the influence of the surfactant system of the lung in controlling the interstitial space hydrostatic pressure while the fluid exchange model determines the influence of the interstitial space hydrostatic pressure in regulating fluid movement across the pulmonary-capillary wall. This model quantitatively estimates the influence of the surfactant alone in regulating fluid movement across the pulmonary-capillary wall

Systems analysis of a closed loop ECLSS using the ASPEN simulation tool. Thermodynamic efficiency analysis of ECLSS components

Our first goal in this project was to perform a systems analysis of a closed loop Environmental Control Life Support System (ECLSS). This pertains to the development of a model of an existing real system from which to assess the state or performance of the existing system. Systems analysis is applied to conceptual models obtained from a system design effort. For our modelling purposes we used a simulator tool called ASPEN (Advanced System for Process Engineering). Our second goal was to evaluate the thermodynamic efficiency of the different components comprising an ECLSS. Use is made of the second law of thermodynamics to determine the amount of irreversibility of energy loss of each component. This will aid design scientists in selecting the components generating the least entropy, as our penultimate goal is to keep the entropy generation of the whole system at a minimum

An estimate of the second law thermodynamic efficiency of the various units comprising an Environmental Control and Life Support System (ECLSS)

The objective of this paper is to present an estimate of the second law thermodynamic efficiency of the various units comprising an Environmental Control and Life Support System (ECLSS). The technique adopted here is based on an evaluation of the 'lost work' within each functional unit of the subsystem. Pertinent information for our analysis is obtained from a user interactive integrated model of an ECLSS. The model was developed using ASPEN. A potential benefit of this analysis is the identification of subsystems with high entropy generation as the most likely candidates for engineering improvements. This work has been motivated by the fact that the design objective for a long term mission should be the evaluation of existing ECLSS technologies not only the basis of the quantity of work needed for or obtained from each subsystem but also on the quality of work. In a previous study Brandhorst showed that the power consumption for partially closed and completely closed regenerable life support systems was estimated as 3.5 kw/individual and 10-12 kw/individual respectively. With the increasing cost and scarcity of energy resources, our attention is drawn to evaluate the existing ECLSS technologies on the basis of their energy efficiency. In general the first law efficiency of a system is usually greater than 50 percent. From literature, the second law efficiency is usually about 10 percent. The estimation of second law efficiency of the system indicates the percentage of energy degraded as irreversibilities within the process. This estimate offers more room for improvement in the design of equipment. From another perspective, our objective is to keep the total entropy production of a life support system as low as possible and still ensure a positive entropy gradient between the system and the surroundings. The reason for doing so is as the entropy production of the system increases, the entropy gradient between the system and the surroundings decreases, and the system will gradually approach equilibrium with the surroundings until it reaches the point where the entropy gradient is zero. At this point no work can be extracted from the system. This is called the 'dead state' of the system

A quantitative estimation of regulation and transport limitations in the human cardiopulmonary system

The object of this dissertation is to quantitatively describe the regulation of some of the exchange processes within the human body. Conceptually this dissertation is divided into two sections. In the first section a macroscopic view was adopted to describe the overall regulation of the cardiovascular and respiratory systems. These overall system models were used as heuristic tools to gain an understanding of physiological behavior in micro-gravity. In the second section, a microscopic view was used to estimate the role played by the surfactant system of the lung in regulating the transfer of fluid across the pulmonary-capillary wall;The basis of the cardiovascular system model is the maintenance of arterial blood pressure homeostasis. Sub-models constituting the overall model are: the pressure-flow model, the heart action model, the controller model which describes short term-control, and the renal model which describes long term control and the regulation of total body water content. Model predictions show that incorporating the fluid shift from the lower to the upper part of the body in micro-gravity is sufficient to account for the cardiovascular changes occurring in micro-gravity;The respiratory model is concerned with the maintenance of a constant carbon dioxide level in the tissue and body fluids. The sub-models constituting the overall respiratory model are: the gas-exchange model, the mechanics model, and the controller model which determines the ventilation and cardiac output on the basis of arterial blood gas tensions. Simulation results show that pleural pressure homogeneity, increased lung diffusing capacity and decreased lung volume are sufficient to describe respiratory changes in micro-gravity;In the penultimate section the lung mechanics model is coupled with a model of fluid exchange across the pulmonary-capillary wall. The lung mechanics model estimates the influence of the surfactant system of the lung in controlling the interstitial space hydrostatic pressure while the fluid exchange model determines the influence of the interstitial space hydrostatic pressure in regulating fluid movement across the pulmonary-capillary wall. This model quantitatively estimates the influence of the surfactant alone in regulating fluid movement across the pulmonary-capillary wall.</p