Device and method for real-time measurement of parameters of mechanical stress state and biomechanical properties of soft biological tissue

Abstract

A device and a method for simultaneous recording, in real time, parameters characterising the mechanical tension, elasticity, dynamical stiffness, creepability and mechanical stress of soft biological tissue are provided. By means of the myometer, a constant external pre-pressure is created, independently of the device's position, between the tissue and the testing end of the device. Next, the tissue is subjected to a short-term external dynamic influence. A mechanical change in the shape of the tissue and its mechanical response are registered as a graph of the tissue's oscillations. For calculating the parameters, a time span on the graph is used which involves an oscillation period from the beginning to the end of the effect on the tissue plus its subsequent first 1.5 self-oscillation period. This enables recording and data-processing to be carried out simultaneously as well as statistically significant estimates to be made in real time.

Claims

1. A device for simultaneous measurement of the parameters characterising the mechanical stress, elasticity, dynamic stiffness, creep and mechanical stress relaxation time of soft biological tissue, comprising: a body, a processor and controller for managing the measuring process and calculating the parameters, a testing end having a movement axis and being movable along its movement axis, a drive of the testing end comprising a movable frame and a solenoid, one end of the testing end being fixed to the movable frame, position sensors for the movable frame, and an accelerometer arranged to sense movement of the testing end, wherein the drive of the testing end is operable in a translational motion having the same direction as the movement axis of the testing end, the movable frame being supported by elastic plate elements so the drive of the testing end is operable with negligible mechanical friction, and the device also comprises light or sound signals arranged to indicate, in response to data from the position sensors, when the elastic plate elements are stress free, when an impulse of current may be transmitted to the solenoid to exert an external impact on the biological tissue; and wherein the controller is arranged such that in use an impulse of current is transmitted to the solenoid to exert the external impact on the biological tissue, after which the biological tissue along with the testing end, the movable frame and the accelerometer undergoes a series of damped oscillations, from which the processor is arranged to calculate the parameters characterising the biological tissue.

2. A device as claimed in claim 1, wherein the moving frame contains a sleeve with permanent magnets placed in the centre of the solenoid, the magnets being oriented with south poles face to face or oriented with north poles face to face.

3. A device as claimed in claim 2, wherein the one end of the testing end that is fixed to the movable frame includes an electrical steel cone-shaped tip that is placed in the pull zone of the permanent magnet which is located closer to the testing end, so said cone-shaped tip is fixed selfrigidly vis-à-vis the movable frame.

4. A device as claimed in claim 3, wherein said device is equipped with a friction-free element for carrying signals from the movements sensor from the movable frame to the processor and controller, the friction-free element being a flexible flat cable.

5. A device as claimed in claim 1 wherein the light signals or sounds signals are placed around an aperture in the body through which the testing end may project.

6. A device as claimed in claim 5, also comprising an arrester system comprising a drive, an actuating screw, a slider moving relative to the body, wherein the slider is equipped with a shutter, and wherein the device comprises stoppers at the extreme positions of the movable frame, together with position sensors mounted on the body.

7. A device as claimed in claim 1 wherein the elastic plates have one ends inflexibly to the movable frame and the other ends are inflexibly fastened to the body.

8. A method for simultaneous measuring, in real time, of the parameters characterising soft biological tissue's mechanical stress, elasticity, dynamic stiffness, creep and mechanical stress relaxation time, by use of a device as claimed in claim 1, comprising the following stages: A. on the surface of soft biological tissue under investigation a means is attached for marking an area of the soft biological tissue to be examined and for joining the testing end of the device with the biological tissue with neither damaging the latter's integrity nor changing its functions, B. the soft biological tissue is externally impacted by a single constant impulse of electric power from the solenoid, which ends with a quick release, C. the mechanical deformation of the tissue and the tissue's subsequent mechanical response are recorded in the form of a graph, e.g. an acceleration graph, of the tissue's natural oscillation, D. on the basis of the acceleration graph, the parameters of the tissue's mechanical stress, elasticity and dynamic stiffness are calculated, wherein the following procedures are performed: in Stage A 1) either to the testing end of the device, or to the surface of the tissue the means is attached for marking the area to be investigated and for joining the testing end with the tissue without either damaging the integrity of the tissue or changing its function, and the testing end is placed on the surface of the soft biological tissue under investigation; 2) the device is brought near the surface being measured, in the course of which the device causes, irrespectively of its position, gravitational field and user, a constant external influence (pre-pressure) between the tissue under investigation and the testing end with force equalling the weight of the mechanism of the testing end, and the pre-pressure is maintained during the stages B-D throughout the whole series of measurements; 3) nearing the device to the tissue is stopped when a necessary pre-pressure has been achieved and the elastic elements are stress-free, i.e. the preconditions for starting a series of measurements have been met; in stage B the device exerts an external impact on soft biological tissue for a prescribed number of times by means of a single constant electric power impulse from the solenoid, wherein each impact ends with a quick release, and the device is held in the same position throughout the measuring series until the end of the measuring series; in stage C the mechanical deformation of the tissue and subsequent mechanical response are recorded in real time in the form of a graph of the tissue's natural oscillations in stage B after each single impulse; in stage D are additionally calculated, in real time, the parameters characterising the creep and mechanical tension relaxation time together with statistical assessments of all the calculated parameters, wherein for calculating the parameters characterising the soft biological tissue's mechanical state of stress, elasticity, dynamic stiffness, creep and mechanical stress relaxation time the time span from the tissue's natural oscillations graph is used which involves the oscillation period from the start until the end of the impact and subsequent 1.5 (one and a half) periods of the tissue's natural oscillation.

9. The method according to claim 8, wherein at stage B the specific power of a single external mechanical impulse ranks between 0.01 and 0.2 W/mm.sup.2, the quick release lasts between 0.1 and 15 ms, and the time taken to achieve maximum impulse is between 1 and 5 ms.

10. The method according to claim 8, wherein the time interval between performing single measurements of a measuring series does not exceed one (1) second and the measurements are performed as many times as necessary for statistical assessment.

Description

DESCRIPTION OF DRAWINGS

(1) FIG. 1 Principal schematic representation of the device.

(2) FIG. 2 Graph of soft biological tissue's natural oscillation, where t.sub.T—instant at which the drive of the testing end starts impacting the soft biological tissue mechanically; t.sub.S—the drive of the testing end is switched off; t.sub.1—the beginning of the mechanical influence of the soft biological tissue on the testing end; t.sub.2—the end of the restoration of its former shape by the soft biological tissue; t.sub.1-t.sub.T—duration of the mechanical impact on the soft biological tissue; t.sub.R-t.sub.1—time taken by the soft biological tissue to restore its former shape after deformation; a.sub.1-maximum acceleration of deformation of the soft biological tissue; t.sub.4-t.sub.1—1.5 natural oscillation periods; a—graph of the acceleration of the testing end; v—graph of the velocity of the testing end; s—graph of the trajectory of the testing end.

DESCRIPTION OF THE EMBODIMENTS

(3) The device for recording the state of mechanical stress and biomechanical properties of soft biological tissues (FIG. 1) comprises the body 1, with a means at its top holding a processor and controller for monitoring the measuring process and for calculating the parameters (a control means 2), a recorder 3 and a moving frame 9 fastened to an inflexible base 13 by an elastic element, such as elastic plates 10 and 11. The moving frame 9 incorporates a sleeve 14 containing two permanent magnets 15 and 16, whose same-name poles are oriented face to face, while the testing end 4 has been attached to the permanent magnet 16 by means of a cone-shaped end 17 made of either electrical steel or some other suitable material. To the bottom part of the moving frame 9, a acceleration sensor 3 has been inflexibly fastened and to the middle of the frame, a shutter 8.

(4) Above and beneath the shutter 8, the position sensors 6 and 7, respectively, have been inflexibly fastened to the body 1. In the upper and lower parts of the moving frame 9 are located inflexibly fastened stoppers 25 and 26.

(5) The arresting system of the moving frame 9 comprises a drive 20, an actuating screw 21, a slider 22 with a shutter 23 and a means 24 for preventing mechanical damage to the arresting system. Along the axis of movement of the arresting system are placed position sensors 27 (upper), 28 (middle) and 29 (lower), which are inflexibly connected with the body 1.

(6) A solenoid 5 has been inflexibly fastened to the body 1, lying in the middle of the moving frame 9.

(7) When the measuring process is triggered by turn of the switch 31, the solenoid 5 is activated by electric current directed by the signal picked up from the axis of the acceleration sensor 3, depending on how the body 1 is oriented in the gravitation field. Constant current in the solenoid 5 gives rise to a constant force affecting the two permanent magnets 15 and 16 located in its magnetic field, as a result of which constant pressure is exerted on the slider 22 by the stopper 25 of the moving frame 9. (This pressure is subsequently conveyed by the testing end 4 to the biological tissue being measured.) Subsequently, the position sensors 6 and 7 of the moving frame 9 are activated, and the slider 22 is positioned by means of the drive 20 and actuating screw 21 from the topmost to the middle position determined by the position sensor 28. As a result, the shutter 8 of the moving frame 9 will expose the light beam proceeding from the position sensor 6 (in the measuring position vis-à-vis the body 1), and cover the light beam proceeding from the position sensor 7 (vis-à-vis the body 1); the testing end 4 will emerge from the opening in the body and the signal lights surrounding the aperture 19 in the testing end will be switched on. Starting from this moment, the device is ready to perform measurements.

(8) The method applied when using the device comprises the following. To carry out measurement, the testing end 4 is placed on the tissue 30 under investigation, causing a deformation ΔS (FIG. 2). Next, the body 1 of the device is moved towards the tissue until the discontinued beam of light from the position sensor 7 (in the measuring position vis-à-vis the body 1) is exposed by the shutter 8, whereas the shutter 8 has not yet covered the light beam proceeding from the sensor 6 (in the measuring position). In the position when the shutter 8 is between the position sensors 6 and 7 and has not yet covered their beam of light, the colour of the light proceeding from the aperture 19 changes, indicating the position of the moving frame 9 in which the elastic plates 10 and 11 are stress-free. Subsequently, impulses of current with a fixed shape, duration and frequency are transmitted to the solenoid 5.

(9) Following each impulse, the soft biological tissue undergoes a dynamic transformation Δl (FIG. 2), which ends with a quick release, after which the biological tissue 30, in accordance with its elasticity properties, undergoes a series of free damping co-oscillations along with the testing end 4, the moving frame 9, and the recorder 3. The tissue's natural oscillation is registered by the recorder 3, and the processor will calculate, in real time, the parameters characterising the tissue's mechanical stress and biomechanical properties, as well as the criteria required for assessment.

(10) If during the measuring session the device leaves the space between the sensors 6 and 7 marking the measuring position of the moving frame 9, or if one of the named position sensors' beams is discontinued by the shutter 8, then the control means 2 of the device will stop the measuring process and the colour of the light will change. The initial colour of the light source will not be restored, unless the position of the moving frame 9 with respect to the sensors 6 and 7 of the measuring position is restored and the measuring session can resume from where it stopped.

(11) After the measuring session has been completed, the arresting system will fix the moving frame 9 in its upper limiting position.

(12) By means of the above device and method the parameters of the biomechanical properties of the state of mechanical stress—elasticity, dynamic stiffness, creepability and mechanical stress relaxation time—were measured in the Biceps brachii, Flexor c.rad., Extensor digitorum muscles and Tendo calcanei simultaneously in real time, after which the data were processed and statistical assessment made.

(13) The named procedures were performed as follows:

(14) Stage A 1) To the testing end of the device (myometer) described above a marker was fastened for marking the area chosen for measurement and for connecting the testing end with the muscle being measured without changing the integrity and function of the biological tissue, i.e., without damaging the tissue, and the testing end was then placed on the surface of the soft tissue to be measured; 2) the device indicated in item 1) was then brought close to the surface being measured until the device's light or sound signal changed; 3) next, irrespective of the position of the device vis-à-vis the gravitation field, an external influence was exerted on the tissue by the testing end by a force equalling the weight of the testing end mechanism; thus, a static deformation ΔS of the tissue was brought about (FIG. 2); 4) the device was held in the same position (for a prescribed time period) until the light or sound signal changed.

(15) Stage B

(16) An external impact was exerted on soft biological tissue by a single constant electrical impulse of the solenoid, which ended with a quick release, while the elastic element of the device was stress-free. The specific power of the impulse was 0.1 W/mm.sup.2, the quick release lasted 0.1 ms, and the maximum of the impulse was achieved in 3 ms. As a result, the dynamic transformation Δl was caused on the tissue (FIG. 2).

(17) Stage C

(18) The mechanical transformation of the tissue was recorded together with the tissue's subsequent mechanical response in the form of a acceleration graph of the tissue's natural oscillation. The recordings were performed a certain prescribed number of times within intervals less than 1 sec (FIG. 2).

(19) Stage D

(20) On the basis of the acceleration graph of the tissue's natural oscillation, in real time and simultaneously, the parameters of the measured tissue's mechanical stress, elasticity, dynamic stiffness and mechanical stress relaxation time were calculated, using the time span on the natural oscillations acceleration graph which consisted of the oscillation period starting with the impact and lasting until its end plus subsequent 1.5 periods of the tissue's first natural oscillation.

(21) The natural oscillation diagram, results of measurement and the orientation of the device were stored by means of a computer program in the memory of the device.

(22) The repeated measurements were carried out after min. 1-second intervals for a sufficient number of times for making statistical estimations. The results were displayed on the LCD screen of the recorder.

(23) The acceleration curve obtained by measurements made by the device (myometer) described above (FIG. 2) enabled calculation of the natural oscillation f of the oscillating muscle mass (together with the mass of the testing end), which is expressed as the inverse value of the oscillation period T
f1/T [Hz],
dynamic stiffness C=m.sub.t*a.sub.1/Δl [N/m],
where m.sub.t—is the mass of the moving part in kg, a.sub.l—acceleration at the time when the testing end is dug deepest in the tissue—m/s.sup.2,
logarithmic decrement
Θ,=ln(a.sub.1/a.sub.3).

(24) Also, it became possible to calculate, in the myometric method described above, the relaxation time t.sub.rel of the tissue, which is expressed by the formula
t.sub.rel=t.sub.2−t.sub.1.

(25) The Deborah number characterising the creepability of the tissue was calculated by the following formula:

(26) $D_e=\frac{t_2-t_1}{t_1-t_T}$

(27) The results of the measurement are given in Table 1 below.

(28) TABLE-US-00001 TABLE 1 Measurements of the muscle tone and biomechanical properties of a 24-year-old male athlete at rest. Side Dynamic Relaxation of Frequency stiffness time Object body Statistics Hz Decrement N/m Creepability ms Biceps Right Average 13.15 1.17 192 1.36 22.65 brahii Median 13.14 1.18 193 1.36 22.50 St-deviation 0.23 0.04 7.9 0.06 0.97 Var. coeff % 1.76 3.60 4.1 4.36 4.27 Left Average 12.93 1.13 180 1.33 22.28 Median 12.99 1.13 180 1.33 22.20 St-deviation 0.17 0.02 4.0 0.04 0.39 Var. coeff % 1.32 2.16 2.2 2.73 1.74 Student t-test (<5%) YES YES YES YES NO Extensor Right Average 15.22 0.81 216 1.01 16.94 digitorum Median 15.28 0.79 218 1.01 16.90 St-deviation 0.30 0.05 12.7 0.04 0.53 Var. coeff % 1.98 5.87 5.9 4.09 3.11 Left Average 14.24 0.97 192 1.17 19.48 Median 14.29 0.97 195 1.20 19.70 St-deviation 0.22 0.02 8.5 0.07 0.74 Var. coeff % 1.57 2.38 4.4 6.37 3.82 Student t-test (<5%) YES YES YES YES YES Flexor Right Average 15.66 1.35 247 1.05 16.84 carpi Median 15.69 1.35 247 1.06 16.90 radialis St-deviation 0.13 0.03 6.1 0.03 0.27 Var. coeff % 0.83 2.12 2.5 2.43 1.59 Left Average 15.80 1.30 253 0.97 15.65 Median 15.80 1.29 253 0.96 15.60 St-deviation 0.29 0.06 9.9 0.04 0.53 Var. coeff % 1.83 4.58 3.9 3.87 3.40 Student t-test (<5%) NO YES YES YES YES Tendo Right Average 30.32 1.11 605 0.44 6.50 calcanei Median 30.77 1.18 607 0.45 6.60 St-deviation 0.96 0.13 12.1 0.01 0.15 Var. coeff % 3.15 11.24 2.0 2.42 2.26 Left Average 35.09 1.04 672 0.38 5.59 Median 35.16 1.03 671 0.38 5.60 St-deviation 0.41 0.02 12.6 0.01 0.15 Var. coeff % 1.17 1.93 1.9 3.52 2.74 Student t-test (<5%) YES YES YES YES YES

(29) Due to the small values of standard deviation, the differences between the parameters of the right and left side of the body are statistically significant even in the case of small values, which shows the great sensitivity and accuracy of the device. The decrement characterising the elasticity of tendo calcanei of the left side of the body has 11.24% variation, calling for the need to repeat the measurement and disclose what causes the instability before appearance of pathological symptoms.

(30) TABLE-US-00002 TABLE 2 Statistical indices of the measurements performed on the test body SonarAid130 by the device of the closest prior art and the device corresponding to the invention, (n = 30). Dynamic Relaxation Statistical Frequency Logarithmic stiffness time Device parameter Hz decrement N/m Creepability ms Device Average 22.12 0.65 500 — — of the Mediaan 22.1 0.66 501 — — closest Standard 0.13 0.02 9 — — prior dev. art Var. coeff % 0.59 3.07 1.8 — — Device Average 22.98 0.29 391 0.78 9.81 of the Median 23.02 0.29 395 0.78 9.7 current Standard 0.15 0.01 13.28 0.02 0.18 invention dev. Var. coeff % 0.64 2.72 3.4 2.78 1.88

(31) By comparing the measurements performed on the test body by means of the prior art and the device corresponding to the current invention it appeared that the decrement was twice as small when measuring by the device corresponding to the invention, which points at the named device's substantially higher sensitivity.

(32) Application of the device corresponding to the invention, the method and the computer program enables one to measure simultaneously, in real time, soft biological tissue's mechanical stress and parameters characterising its four biomechanical properties —elasticity, dynamic stiffness, creepability and mechanical stress relaxation time; measure and assess the state of stress and biomechanical properties of soft biological tissue with greater accuracy; repeat the measuring procedure within small time intervals, as the parameters for impacting on soft biological tissue by means of a single impulse are chosen so that in the course of measurements they will change neither the stress nor biomechanical properties of the tissue under investigation; perform measurements at different angles, maintaining the constant pre-pressure when doing so; measure following a prescribed algorithm; obtain, owing to good repeatability of measurements, within a short period of investigation, a sufficient number of measurements for statistical evaluation and/or comparison of the state of soft biological tissues with reference values; obtain standardised criteria of assessment which are released by the firmware immediately after completion of the measurements; raise the sensitivity of the device; reduce the user's influence on the measurements.