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Viscoelasticity and fractal structure in a model of human lungs

Ionescu C. M., Kosinski W., Keyser R. de

Archives of Mechanics

2010

Vol. 62, nr 1

21-48

This paper provides a model of the human respiratory system by taking into account the fractal structure of the airways and the viscoelastic properties of the tissue. The self-similarity of airway distribution is admitted up to the 24th generation. Due to periodic breathing which results in sinusoidal excitation of the respiratory system, an electrical equivalent model is developed. The periodic current in this electrical network, that preserves the geometry of the human respiratory tree, is equivalent to the oscillatory air-flow. The model is expressed by Navier-Stokes equations under cylindrical symmetry, linked with an equation responsible for the motion of viscoelastic tissue of airway walls. By use of both electro-mechanical analogies, the total impedance of the respiratory system is determined and compared to the measured data in the clinical range of 4-48 Hz, as well as in the low-frequency range of 0.1-5 Hz. We propose also a lumped model of fractional orders, which is able to capture frequency-dependent variations in both clinical as well as in the low-frequency ranges. The models proposed in this paper can be further used to determine the effects of disease on the lung morphology.

Some challenging feedback-control applications in biomedical systems

Ionescu C., Keyser R. de

Journal of Medical Informatics & Technologies

2005

Vol. 9

35--46

Natural biological control involves the normal functioning of the living organism (i.e. human body) to regulate its parameters such that the vital functions are kept within the normal operating range. When this natural control fails, the biological feedback (thus a closed loop system) is unstable and/or operates under non-optimal conditions of the vital capacity of the subject. In this context, ensuring surviving capacity of the subject implies to artificially control the vital functions presenting the functional failure. Nowadays technology enables development of artificial closed loop devices to correct and provide the normal functions of the organism, replacing thus the damaged/non-optimal parts or helping in recovering their natural properties (rehabilitation techniques). Two of the most en-vogue applications of artificial control will exemplify the importance and the posed challenges: - a neuroprothesis device to control paralyzed skeletal muscles; this enables rehabilitation of drop-foot or hand-grasp movements with paretic or paralyzed skeletal muscles by use of a self-adaptive (auto-tuning) control strategy; - and an artificial pancreas for diabetes type I patients; the blood glucose control in diabetic patients type I is made by use of an in-house developed model-based predictive control algorithm in which input (insulin rate) and output (glucose level) are constrained.