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Modelling and Control of Therapeutic System Using “Assumption Based Truth Maintenance System”
Copyright e IFAC Modeling and Control in Biomedical -
Systems. Galvestm. Te.xu. USA. 1994
MODELLING AND CONTROL OF THERAPEUTIC SYSTEM USING "ASSUMPTION BASED TRUTH MAINTENANCE SYSTEM" S. Ravichandran, G.N.S. Prasad Department of Physics. Anna University, Madras - 600 025
ABSTRACf The salient features of a model based system in electrotherapy are discussed in this paper. The general frame-work of this dedicated model based system is to identify a device model and sub-system to set appropriate modules for diagnosis and therapy and to provide the control knowledge for selecting the appropriate facets of the model based on stimulation parameter, habituation response and type of electrode array. This system is not only effective but also optimally simple and in fact it has been observed that these qualitative reasoning methods are complete and do not miss any real value solution in spite of simplifying assumptions.
INlRODUCTION In the nueromuscular system most nerve fibres are stimulated by low-frequency currents in the range 1 Hz to 200 Hz. At low intensities these low frequency currents are not suitable to influence a target site in the depth of the tissue due to high resistance offered by the outer coroniallayer of the skin. At high intensities these low-frequency currents can cause ulceration of the skin under the electrodes due to electrolysis of the fluid in the tissue [2]. Unlike low-frequency currents, midfrequency currents have a penetrating property and reach deeper tissues and are well tolerated by the skin. When the nerve fibres are stimulated with continuous mid-frequency currents in the range 1 KHz to 8 KHz, the depolarisation of the nerve no longer coincides with the frequency of stimulation and this asynchronised depolarisation leads to Inhibition of reaction to stimulaThis tion causing fatigue of motor-end-plates[ 1/1 ]. inhibition can be overcome by Interrupting the mldfrequency currents after each polarisation so that repolarisation can then be effected making the tissue sensitive to stimulation. Thus Interrupted mid-frequency currents This work was supported by Kody Medical Electronics Ltd., Madras and Tamilnad Hospitals Ltd., Madras.
429
have the penetrating property to reach deeper tissues and also provide synchrOnised stimulation of excitable tissues. Since different excitable tissues propagate at widely different speeds, It is desirable to treat each of these tissues with the optimum frequency of excitation and hence there is a need to optimise the frequency swing of the interrupted mid-frequency currents. A comprehensive study of habituation response is a prerequisite In therapy as it has been widely observed that habituation response is a limiting factor in mid-frequency therapy. In order to formulate the required midfrequency band, interrupting low-frequency band, spectrum program for providing the frequency swing and spectrum time to govern the duration of swing based on habituation response test, a general framework has been designed to provide a suitable model In each situation based on qualitative reasoning, governed by the truth maintenance system.
SYSTEM DESIGN The system console has a programmable array of keys which provides the main framework for selecting hard-wired models from the system shell. It is possible to configure a model, sub-system and supporting modules with the help of the console. The present design has scope for prOviding more than 200 modules which can be utilised for configuring an appropriate model. There is a facility to select 32 spectrum programmes which have been found useful in manipulating the frequency swing. Spectrum time for modulating mldfrequency currents can be programmed through the console and thus a new module can be created by selecting a spectrum time with a suitable spectrum programme. Since the general framework of the system has been designed for electrotherapy with mid-frequency and low-frequency currents it is interfaced with supporting hardware such as precision mid-frequency generator specially developed for providing frequencies and programmable through the system console. These frequency modules have been tested for long term stability. The remaining part of the system
BLOCK DIAGRAM OF A SYSTEM
THE BASIC IDEA OF MODEL-BASED SYSTEM
System Console with Keys for selection
~ Hard-wired Module Bank
Control System
, Interface for Mid-frequency Generators
Supporting Hard/ ware for Electrode Interface ~
~
consists of line drivers, amplifiers, an Isolating system and an electrode array selector. The line drivers and amplifiers have been designed to interface mldfrequency currents to the Isolating system which Interfaces the electrode array selector. The electrode array selector provides the patient interface and this selector is programmable through the system console. The system also has modules for performing habituation response time tests. In this general framework, a component model cannot be considered as a simple monolythlc description. It has to organise many different "facets" and their relationships. The driving force for splitting the model is the goal of using In each situation, a model that is effective but also as simple as possible. Habituation response test can be performed in this system In each case for selected mid-frequency bands and for selected models. The response In each case for each model can be tabulated on the 10 point habituation response index scale (HRIS) which provides the basis for the right paradigm in therapy. The HRIS scale has been newly introduced In practise as the decision on treatment parameters is governed by this scale. A number of qualitative modelling techniques have been developed and used In proto-typlca1 systems. Some of them need to be further developed and to be tested in real-time applications.
430
CONCLUSION Interrupted mid-frequency currents In the frequency band [1 KHz - 8 KHZ] have been used in the present design and the distribution of currents in the electrode array Is programmable through the system console based on qualitative models. This system obeying ATMS table and HRIS scale has been found beneficial In overcoming the habituation response to a great extent The techniques presented are more promising In the treatment of single sited and diffussed pain sites at optimum intensities without an unpleasant stimulus.
REFERENCES 1. Lullies H. Und D. Trincker, "Taschenbuch der Physiologie 11", Pages - 97, 98, 72 and 182. 2. Ravichandran. S "Recent Advances in Interferential Current Therapy" Proc. lEEEIEMBS Pages 2313 - 2314 Vol. 12 No.5 November 1990 3. Ravichandran. S. G.N.S. Prosad "Advances In Electrokinesy with Programmable Macro Electrode Array System" Proc. lEEEIEMBS Conference, Paris, OctINov.1992.
Systems. Galvestm. Te.xu. USA. 1994
MODELLING AND CONTROL OF THERAPEUTIC SYSTEM USING "ASSUMPTION BASED TRUTH MAINTENANCE SYSTEM" S. Ravichandran, G.N.S. Prasad Department of Physics. Anna University, Madras - 600 025
ABSTRACf The salient features of a model based system in electrotherapy are discussed in this paper. The general frame-work of this dedicated model based system is to identify a device model and sub-system to set appropriate modules for diagnosis and therapy and to provide the control knowledge for selecting the appropriate facets of the model based on stimulation parameter, habituation response and type of electrode array. This system is not only effective but also optimally simple and in fact it has been observed that these qualitative reasoning methods are complete and do not miss any real value solution in spite of simplifying assumptions.
INlRODUCTION In the nueromuscular system most nerve fibres are stimulated by low-frequency currents in the range 1 Hz to 200 Hz. At low intensities these low frequency currents are not suitable to influence a target site in the depth of the tissue due to high resistance offered by the outer coroniallayer of the skin. At high intensities these low-frequency currents can cause ulceration of the skin under the electrodes due to electrolysis of the fluid in the tissue [2]. Unlike low-frequency currents, midfrequency currents have a penetrating property and reach deeper tissues and are well tolerated by the skin. When the nerve fibres are stimulated with continuous mid-frequency currents in the range 1 KHz to 8 KHz, the depolarisation of the nerve no longer coincides with the frequency of stimulation and this asynchronised depolarisation leads to Inhibition of reaction to stimulaThis tion causing fatigue of motor-end-plates[ 1/1 ]. inhibition can be overcome by Interrupting the mldfrequency currents after each polarisation so that repolarisation can then be effected making the tissue sensitive to stimulation. Thus Interrupted mid-frequency currents This work was supported by Kody Medical Electronics Ltd., Madras and Tamilnad Hospitals Ltd., Madras.
429
have the penetrating property to reach deeper tissues and also provide synchrOnised stimulation of excitable tissues. Since different excitable tissues propagate at widely different speeds, It is desirable to treat each of these tissues with the optimum frequency of excitation and hence there is a need to optimise the frequency swing of the interrupted mid-frequency currents. A comprehensive study of habituation response is a prerequisite In therapy as it has been widely observed that habituation response is a limiting factor in mid-frequency therapy. In order to formulate the required midfrequency band, interrupting low-frequency band, spectrum program for providing the frequency swing and spectrum time to govern the duration of swing based on habituation response test, a general framework has been designed to provide a suitable model In each situation based on qualitative reasoning, governed by the truth maintenance system.
SYSTEM DESIGN The system console has a programmable array of keys which provides the main framework for selecting hard-wired models from the system shell. It is possible to configure a model, sub-system and supporting modules with the help of the console. The present design has scope for prOviding more than 200 modules which can be utilised for configuring an appropriate model. There is a facility to select 32 spectrum programmes which have been found useful in manipulating the frequency swing. Spectrum time for modulating mldfrequency currents can be programmed through the console and thus a new module can be created by selecting a spectrum time with a suitable spectrum programme. Since the general framework of the system has been designed for electrotherapy with mid-frequency and low-frequency currents it is interfaced with supporting hardware such as precision mid-frequency generator specially developed for providing frequencies and programmable through the system console. These frequency modules have been tested for long term stability. The remaining part of the system
BLOCK DIAGRAM OF A SYSTEM
THE BASIC IDEA OF MODEL-BASED SYSTEM
System Console with Keys for selection
~ Hard-wired Module Bank
Control System
, Interface for Mid-frequency Generators
Supporting Hard/ ware for Electrode Interface ~
~
consists of line drivers, amplifiers, an Isolating system and an electrode array selector. The line drivers and amplifiers have been designed to interface mldfrequency currents to the Isolating system which Interfaces the electrode array selector. The electrode array selector provides the patient interface and this selector is programmable through the system console. The system also has modules for performing habituation response time tests. In this general framework, a component model cannot be considered as a simple monolythlc description. It has to organise many different "facets" and their relationships. The driving force for splitting the model is the goal of using In each situation, a model that is effective but also as simple as possible. Habituation response test can be performed in this system In each case for selected mid-frequency bands and for selected models. The response In each case for each model can be tabulated on the 10 point habituation response index scale (HRIS) which provides the basis for the right paradigm in therapy. The HRIS scale has been newly introduced In practise as the decision on treatment parameters is governed by this scale. A number of qualitative modelling techniques have been developed and used In proto-typlca1 systems. Some of them need to be further developed and to be tested in real-time applications.
430
CONCLUSION Interrupted mid-frequency currents In the frequency band [1 KHz - 8 KHZ] have been used in the present design and the distribution of currents in the electrode array Is programmable through the system console based on qualitative models. This system obeying ATMS table and HRIS scale has been found beneficial In overcoming the habituation response to a great extent The techniques presented are more promising In the treatment of single sited and diffussed pain sites at optimum intensities without an unpleasant stimulus.
REFERENCES 1. Lullies H. Und D. Trincker, "Taschenbuch der Physiologie 11", Pages - 97, 98, 72 and 182. 2. Ravichandran. S "Recent Advances in Interferential Current Therapy" Proc. lEEEIEMBS Pages 2313 - 2314 Vol. 12 No.5 November 1990 3. Ravichandran. S. G.N.S. Prosad "Advances In Electrokinesy with Programmable Macro Electrode Array System" Proc. lEEEIEMBS Conference, Paris, OctINov.1992.