Patent No. 3789834 Processes and apparatus for the investigation of internal physiological phenomena based on measurements of the impedance variation of the surface of the body

 Patent No. 3789834 

Processes and apparatus for the investigation of internal physiological phenomena based on measurements of the impedance variation of the surface of the body (Duroux, Feb 5, 1974)

Abstract

A method of investigating physiological phenomena of a portion of a body based upon the variation of the impedance or resistivity of the body. An electromagnetic field is applied to a portion of the body and the field at the surface of the body is then measured. The components of the measured field are used to determine the impedance or resistivity of the the body.

Notes:

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention concerns an improvement in or relating to processes used in medicine for the study of internal physiological phenomena based on the measurements of the variation of an impedance measured on the surface of the body.

2. Description of the Prior Art

For several years, examination of pulmonary ventilation, respiratory frequency, cardiac output, the water content of the extravascular sector, lungs or peripheral interstitial tissue, for supervising transfusions and perfusions on operated patients and, again, examination of the circulation in the kidneys, the brain, a limb or other part of the body excluded from or during and following surgical intervention, have resulted in the measurement and study of the variations of the impedance Z = V.sub.M - V.sub.N /I, in which V.sub.M - V.sub.N is the voltage picked up between two electrodes M and N, and I the current injected between two other electrodes A and B. The electrodes used for this purpose may be applied to different parts of the body: head, neck, thorax, abdomen, limbs.

The measurement of the differential of the impedance with respect to time dZ/dt is also utilized, being applicable for example to the examination of the contraction of the cardiac muscle and to the recognition of the reciprocal actions of the P (auricle) waves and the QRS (ventricle) complexes.

However, these methods have a number of appreciable disadvantages which may be imputed first of all to the difficulty of obtaining good contacts between electrodes and skin. In addition because of the difficulties of positioning these electrodes, the contact resistance is variable and the effect of the variations of contact resistance therefore, may, being superimposed on the influence of the parameters of internal origin which it is desired to study, make the measurements suspect. Furthermore, the necessary use of large electrode devices involves the exploration of over-extensive areas, thus rendering the examination unselective. To sum up, despite the advantages of this process, in that it avoids the use of methods of investigation involving blood letting, thus eliminating the danger, the measurement of the impedance is lacking in precision, the ratio of signal to noise is often very poor and, in certain cases, such as the study of cardiac output, for example, the results are masked by the coupled effect of respiration.

SUMMARY OF THE INVENTION

The principle object of the present invention is an improvement to the process of investigating physiological phenomena based upon the impedance variations relative to the variations of the electrical resistivity of a predetermined volume of the body and to devices for carrying out the process. The invention is characterized in that the patient is subjected to an electro-magnetic field having a frequency between 10kHz and 100MHz or more, the source of which is localized relative to the part of the body to be examined and the frequency is regulated to define the precise volume of the part of the body to be examined. At least one component of the electro-magnetic field in the vicinity of the volume is picked up for calculating an impedance function, the values of which are registered in order to ascertain the rate of propagation.

This improvement to the conventional investigation process has, as its principal advantage, great precision in carrying out the investigation by virtue of the precision with which a narrow volume can be selected in a direction indicated by positions of the source and the field pick-ups, the depth of the zones affected by the radiation being determined by simple control of the radiation frequency. Furthermore, the four relatively large electrodes applied to the skin in the earlier processes are eliminated. A process is then obtained involving great precision in the measurements, a better signal to noise ratio permitting the use of simple and miniaturizable devices, very precise localization of the area to be studied and easier separation of the various combined effects: pulmonary or cardiac, for example. Since there is no danger to the patient, the process may be applied in the continuous supervision of any seriously affected patient.