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MECHANICAL IMPEDANCE |
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General information |
GENERAL INFORMATION Impedance characteristics
of biological soft tissues are determined in experiments on touching tissues
by a small, hard, vibrating indentor on the basis of measurements of indentor
kinematics parameters (displacement (U), velocity (V) or
acceleration (A)) and resistance force to tissue deforming (F).
For the complete description of tissues behavior in these experiments one can
use real and imaginary parts of any of three equal characteristics: complex
stiffness K = -F/U, complex mechanical impedance Z = -F/V
and complex inertia M = -F/A - or any pair of independent values, in
particular, real parts of stiffness and impedance (ReK and ReZ).
Studies of impedance characteristics of biologic soft tissues have been
performed for a long time, but only recently they were given a new impetus
owing to the development of modern computer measurement facilities and data
processing. Such studies began as far back as 40-th in connection with the
problem of different contact sensors matching with the human body surface. A
bit later studies of dependencies of impedance characteristic on tissue
conditions and development of ways of evaluation of these conditions on the
basis of impedance measurements began. New trends of work within the
framework of these studies are development of the method to reconstruct
mechanical parameters of multi-layered tissues on the basis of spectral
impedance measurements, that is to say on the basis of frequency dependencies
of impedance characteristics, and development of the method of continuous monitoring
of tissues viscoelastic parameters with high time resolving power on the
basis of single-frequency impedance measurements. These methods offer new
opportunities of tracking the changes of tissues viscoelastic
characteristics, in the first place muscles, in the course of various
physiological and pathological processes and in the course of the development
of response to different test influences. Thereby, new opportunities are
being offered for biomechanical and medical study of human neuromuscular
system, for example, when studying the mechanism of the motor control or when
studying an action of various drugs. A cycle of theoretical
and experimental work was performed during the several last years in IAP RAS
on the interaction of vibrating indentor with biological tissues. Besides, a
set of portable and computer-based devices was developed for measuring
mechanical impedance of tissues, as well as a series of studies was performed
of surface tissues of human body by the impedance measuring method. |
