identification in cybernetics

From Big Medical Encyclopedia

IDENTIFICATION in cybernetics (late lat. to identify identificare) — creation of model of system according to its functioning.

Methods I. are applied to creation of models of cardiovascular system, the blood circulatory system, change of duration of action potential of fibers of a myocardium in the course of assimilation of a rhythm, structure of the motive device, assessment of a condition of a hemodynamics of a brain, automatic diagnosis of heart diseases, dynamics of hormones of a thyroid gland, dynamics of pressure of blood, immune responses of the person, etc.

For creation of model by methods I. information which is contained in entrance and output variables of an object is usually used. So, at And. process of treatment entrance variables are data on the carried-out therapy (amount of medicines, frequency of their reception, etc.), and days off — indicators of a condition of the patient (temperature, pulse, arterial pressure, results of visual survey etc.). And. standards of the ECG it is carried out by results of averaging of quantitative values of a voltage, height of teeth, intervals, etc. at healthy people.

Fig. 1. The scheme of conditional representation of reaction of a real object «A» which can be the phenomenon, process, a live or artificial object of a research, on the revolting entrance influence (e.g., an irritant): X (t) — the variable characterizing this influence (e.g., process of treatment); Y(t) — the variable characterizing reaction of an object to the entrance (revolting) influence (e.g., result of treatment).

Result And. the mathematical model describing dynamic properties of a subject to observation is; the equation establishing ratios between entrance and output variables on a basis to-rogo it is possible to estimate the size of reaction of an object to entrance influence, to carry out the choice of structure and parameters of a control system, to estimate its quality and efficiency. For the description of dynamic properties of an object entrance and output sizes are considered as functions of time of t and are designated respectively through X (t) and Y (t). Usually X (t) and Y (t) are considered as stochastic functions of a nonrandom argument of t. The exhaustive characteristic describing dynamic properties of an object is the operator, i.e. any mathematical (differentiation, integration, the solution of the functional equations, etc.) and logical (yes, is not present or other) the actions, rules translating entrance sizes during the week-end. The usual way of schematic representation of an object is shown in the theory of management in the figure 1: entrance function X (t) will be transformed by the object described by operator A to the output Y (t) function. Thus, pattern (operator A) of functioning of an object describes reaction of an object of Y(t) to entrance indignation of X (t) and establishes compliance between Y(t) and X (t), t. e. Y (t) = AX(t). Such representation gives the chance to abstract from the physical nature of entrance and output variables and an object and to develop the general rules of the description and methods of management of objects. Devices, devices, technical, biological processes, the person or group of people, etc. can act as an object.

In certain cases in biology and medicine at And. live organisms for the purpose of problem solving of diagnosis, assessment of norm, pathology, etc. as the main information only implementation of the output Y (t) variables can serve. In this case the task of definition of the equation of communication between Y (t) and X (t) is not set, and the characteristic of output variables and their deviations from normal amounts is defined. This case can be considered as private, and the solution of a task And. comes down to assessment of the telecom operator between the separate output Y(t) variables, napr, at creation of the «norm» and «pathology» models.

Fig. 2. Process flow diagram of identification: the studied object A and the created its model A * receive an identical irritant — X (t); reaction to an irritant at an object A — Y (t), and at its model Y * (t); than less difference between size Y * (t) and Y (t), especially are identical model and an object.

Theory And. develops methods of receiving optimum model of an object, i.e. the best assessment of operator A * on implementation of X (t) and Y (t). In operating conditions of an object measurements of entrance X (t) and output Y(t) of variables are carried out and, thus, receive implementations of these functions (fig. 2). At And. such structure is established and such parameters which give the chance to construct model A *, close to the true operator of an object A are defined. The proximity And * to And is estimated by special mathematical methods (usually value of optimality criterion).

Due to the need of carrying out calculations, big on volume, problem solving And. it is carried out on the COMPUTER (see. Electronic computer ). In the 70th 20 century almost the programs constructed on are developed for all COMPUTERS to algorithms (see) problem solving And., which can be used, in particular, and for And. medicobiological objects (e.g., creation of model of a disease and its use for diagnosis). Besides, for obtaining statistical characteristics of entrance and output variables, and also the solution of a task And. there are specialized COMPUTERS on which process of receiving and information processing is completely automated.

Fig. 3. The scheme of an adaptive control system in a chain of a feed-back: in the course of normal functioning of an object A input data x (t) and output y(t) signals of an object come to the identifier. On these signals in the identifier the model of an object is under construction; when process of identification is finished, the received results are used in a managing part for development of size of management of u(t) (change of a dose and frequency or a way of introduction of drugs, use of new drugs) and for achievement of the set (required) Y3 (t) value.

Wide use methods I. find in a class adaptive (self-adjusted, self-organizing etc.) control systems, and also at automation of a scientific experiment. The identifier which on entrance X (t) and output Y (t) variable carries out specification of model of the condition of an object changing in time is provided in these cases in parallel with an object. The approximate flowchart of adaptive system is provided on the figure 3. Here the identifier is in a chain of a feed-back and by results And. and to a preset value day off of the Y3 (t) variable is carried out definition of the law of management. Usually processes And. and managements are carried out by the same the operating computer (OC) and their division is carried out in the program way. Use of special algorithms And. gives the chance to receive model for difficult objects with a large number of entrance and output variables and characteristics changing in time. With the identifier the automated systems of a scientific experiment, including researches conducted over live organisms in experimental and clinical laboratories have approximately similar structure.

Fig. 4. Scheme of the principle of machine interpretation of an ECG: the electrocardiograph transfers signals of assignments from subject to observation (e.g., the patient) in the COMPUTER (it is designated by a dotted line), in which indications of size of teeth and intervals of an ECG of a subject to observation with an ECG healthy or sick are identified, processed according to the corresponding indications; at the exit of the COMPUTER quantitative results of comparison (size of aberrations) by which the conclusion is drawn turn out.
Fig. 5. Scheme of system of overseeing by the patient: on signals x (t) and at (t) in the identifier the condition of the patient is estimated; it is possible to see signals of observations and results of identification on the screen of a cardiomonitor; at sudden fibrillation of ventricles the identifier includes system of alarm and a defibrillator, managing the size and the moment of the category.

Example of use of methods I. machine interpretation of an ECG (fig. 4) can serve in clinical medicine. On an entrance of the identifier of parameters — signals of assignments of an ECG, at the exit — results of measurement of a voltage and height of teeth and intervals of the electrocardiogram (PQ, QRS, RS—T, T etc.). The last give on an entrance of the identifier of pathology, on escaping to-rogo receive the decision about norm or pathology of an ECG. Splitting into two blocks of identification is conditional and both processes are carried out by one COMPUTER. In the figure 5 use of the identifier is shown in the closed scheme of overseeing by the patient. On an entrance of the identifier data on action of the heart and the carried-out therapy are entered. Its exit is connected to systems of alarm, sighting on the screen, to a defibrillator. At sudden fibrillation of ventricles all systems at the same time join.

In case of disturbances of a rhythm — harbingers of fibrillation — only the system of sighting and alarm joins.

Bibliography: Computing systems and automatic diagnosis of heart diseases, under the editorship of Ts. Cáceres and L. Dreyfus, lane with English, M., 1974; Petrovsky A. M. Systems analysis of some medicobiological problems connected with management of treatment, Automatic equipment and telemechanics, No. 2, page 54, 1974, bibliogr.; P and y m and N. S N. What is identification, M., 1970, bibliogr.

V. N. Raybman, N. S. Raybman.