Russian Academy of Sciences
Institute of Applied Physics

Division of
Radiophysical
methods in medicine

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LOW-FREQUENCY VIBROACOUSTICAL METHODS TO STUDY BIOLOGICAL SYSTEMS.

Historically the first appeared a direction connected with quantitative studies of vibroacoustical activity in cardiovascular system. The essential success of medium 70-th in this direction was a measurement, in laboratory conditions and in the space flight, of absolute values of spectral components of the force, acting on the human body from the working heart. Piezoaccelerometers PAMT and their construction elements, developed for measurement of human body fluctuations in the weightlessness, up to the present time are used not only for medical, as well as for technical vibrational diagnostics.

Since 1980 studies of human body vibrations, accompanying locomotion, were begun for clinical and cosmic medicine. It was shown here that on acceleration spectra, measured on the corresponding areas, it is possible to evaluate the condition of joint surfaces, the decay degree of bone-cartilage complex, the stability of vertical pose, the level of pain syndrome and others. The unknown earlier fluctuations of statically stressed muscles within the 3 kHz frequency range were registered, connected probably with the motion of protein molecules during the muscle contraction.

In connection with the arising problems of interfaces for man-machine systems and of electronic prosthetic devices of organs, the ideas were worded of making the additional sensor channels and new approaches were offered to study functions of analyzers, based on the measurement of casual errors in their work. So, for the biceps it was demonstrated in the experiment that dependency of its tension fluctuations from the value of this tension qualitatively coincides with the Weber-Fechner law, describing the main psychophysical low for the dependency of perception level from the value of stimulus.

Studies of rheological characteristics of biological soft tissues, based on the use of low-frequency (shear) acoustic oscillations and waves, were begun for solving the metrology problems when measuring the human body oscillations by contact transducers, firstly by accelerometers PAMT. It had became clear soon that such studies have an independent interest for checking the fine realignments of tissues internal structure in the course of natural physiological or pathological processes. That opens new possibilities for fundamental studies of neurophysiological mechanisms of checking and control of the condition of human organs and systems.
The main contents of work, which is performed in this direction in IAP, is the development of new facilities and methods to study the low-frequency acoustic waves in biological tissues, as well as the experiments on study the linear and nonlinear shear mechanoacoustical characteristics of tissues in different conditions. From the developed measurement facilities the most significant are: computer-based and portable original meters of stress-strain characteristics and of impedance characteristics of biological tissues, the contact and the remote facilities of checking the parameters of surface waves and of shear waves inside the tissue. They have been used for studies the preparations of rabbit lung, liver and kidney, the human brain tissue during operations, the burn scars, the surface muscles of human in situ on children and adults, on sportsmen, on sick persons with various pathologies, on healthy persons under the external electrical stimulation and in the course of vibrational reflex and of knee reflex.
For the interpretation of measurements and for the analysis of mechanoacoustical characteristics of biological tissues the models have been offered of forming in biological tissues the elastic fields of the vibratory source, as well as the continual and microstructure models of forming the acoustic characteristics of biological tissues.