Measurement of Thoracic Impedance and Approximations: A Diagnosis Technique for Clinical Utilisation

The purpose of this paper is to facilitate the readers and the researchers about the implementations and applications of thoracic impedance measurements and approximations for diagnosis of several related diseases. In this study, two entirely non-invasive approaches and simple assumptions are taken into consideration to measure the transthoracic electrical impedance and lung volume. In the first method, the fluid volume is calculated by considering a pre-defined curve and anthropometric dimensions of the human thorax, whereas in the second method, the thorax is considered as a cylinder and the cylindrical mathematical standard formulae are utilised for approximation of the lung volume. The thoracic impedance is measured directly by placing the tetrapolar electrodes on the right side of the human thorax. The right side of the thorax is considered in order to avoid the incorporation of the geometrical aspects and the behaviour of the heart. The anthropometric dimensions are taken for six normal male subjects of sound health. With the help of these parameters, the thoracic fluid volume is predicted using two methods. In the first method, the thoracic volume is predicted by considering the thorax as a cylinder and by using basic relations of the periphery and volume of the cylinder. Human thorax dimensions are approximated as height and breadth of the cylinder and certain approximations have been adopted. The anthropometric dimensions are taken for the chest at normal resting conditions and at breath-hold positions. In both the approaches, the difference between the measured and the predicted impedances and volumes are clearly observable.