Journal of Medical Engineering & Technology
ISSN: 0309-1902 (Print) 1464-522X (Online) Journal homepage: http://www.tandfonline.com/loi/ijmt20
An evoked compound electromyogram simulator with external microprocessor control facility D. C. Smith To cite this article: D. C. Smith (1992) An evoked compound electromyogram simulator with external microprocessor control facility, Journal of Medical Engineering & Technology, 16:3, 129-132, DOI: 10.3109/03091909209021975 To link to this article: http://dx.doi.org/10.3109/03091909209021975
Published online: 09 Jul 2009.
Submit your article to this journal
Article views: 2
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Full Terms & Conditions of access and use can be found at http://www.tandfonline.com/action/journalInformation?journalCode=ijmt20 Download by: [Australian National University]
Date: 06 May 2016, At: 11:04
Journal of Medical Engineering & Technology, Volume 16, Number 3 (MayIJune 1992), pages 12S132
An evoked compound electromyogram simulator with external microprocessor control facility D. C. Smith?
Downloaded by [Australian National University] at 11:04 06 May 2016
Department of Anaesthesia, Pbmouth General Hospital, Creenbank Terrace, Pbmouth PL4 8QQ UK
A circuit f o r an evoked electromyogram simulator is described, which produces a biphasic triangular waveform similar to the evoked compound action potential seen during clinical quantitative neuromuscular monitoring. The device can produce a fading trainof-fOur sequence, which can be controlled using a single externallyderived voltage. The simulator is useful f o r bench-testing of closed loop muscle relaxant administration systems, and for teaching aspects of neuromuscular monitoring in anaesthesia.
generated 4 ms after each stimulus pulse (figure 1). The delay simulates physiological nerve-muscle conduction time. (3) Output is via a variable-gain buffer amplifier which acts as an envelope shaper. This stage controls the degree of fade, or the decrement in response over time, seen during clinical monitoring of neuromuscular transmission with tctanic or train-of-four stimulation patterns [ 1,2]. T h e simulator output level and fade pattern may be controlled by a single analogue voltage, making it possible to generate the complex onset and offset patterns seen during clinical neuromuscular blockade, or to model a response based upon established pharmacokinetic principles.
Introduction During the development of medical instrumentation systems it is useful to be able to generate signals comparable with those which will be processed in the clinical situation; this allows the designer to investigate the fidelity of reproduction of the applied signal. I n addition, a simulator can act as an ‘artificial patient’ in microprocessor-controlled closed-loop systems, allowing development and testing of such systems to take place in the laboratory, rather than in the clinical situation. The circuit described here has been developed to simulate the cvoked compound muscle action potential (ECAP) observed during the clinical monitoring of neuromuscular transmission by evoked electromyography (EEMG).
Circuit description The circuit is shown in figure 2. Pulses from a physiological nerve stimulator trigger the monostable icla to generate a 4 ms delay pulse, simulating physiological nerve-muscle conduction time. Outputs from icl b then initiate the following functions:
ECAP waveform generator
A low-to-high transition at the input of iclb generates 4.5 ms positive pulses which are applied to a modifi-
A
Design The simulator performs the following functions in response to the output pulses from a physiological nerve stimulator: (1) An optically-isolated trigger input keeps the high voltagc pulses from nerve stimulators out of the simulator circuit. (2) A biphasic, triangular wave of8 ms duration, similar to the physiological compound electromyogram, is 0
2
I
I
4
6
8
I
I
10
12
Time (ms)
?Address for correspondence: Department of Anaesthesia, Western Inznnaiy, Dumbarton Road, Clasgaw C I I GNT. U K
Figure 1. Output waveform produced by the simulator in response to each stimulus pulse f r o m a nerve stimulator. Stimulus pulse occurs at the beginning of the time axis. 129
Downloaded by [Australian National University] at 11:04 06 May 2016
D. C. Smith Evoked compound EMG
icl. ic4 4098 LH32L ic2 k3 CA3080 ic5 TusS5C
simulator
all diodes 1N4148 rxcopl d l 12v ZMW d2 1Sv ZMW
Figure 2. Circuit diagram of the simulator. cation of the simulator circuit described by Lee et al. [3], consisting of ic2a-c. This part of the circuit is a triangular-wave generator, constrained to generate a single cycle in response to each pulse from the nerve stimulator. The simulated ECAP waveform is presented to the transconductance amplifier ic3, where the final amplitude of each simulated ECAP is controlled by an enveloping sequence. Envelope shaping sequence A high-to-low transition at the negative input of monostable ic4a causes its 4 output to go low. Duration of the low state can be varied by vr2 from about 15-1500 ms, the minimum period being determined by the operating characteristics of the 4098 dual monostable. The subsequent return of this output to the high state causes the 4 output of ic4b to go low for 1500 ms. This switches on tl; the collector voltage flips from - 15 to 15 V and remains at + 15 V for 1500 ms (see next section for function of switch ‘a’). The output of ic2d is kept normally at + 12 V by the negative voltage on the input and the action of Zener diodes d l and d2. The Zener diodes ensure that when tl switches there is no delay due to output saturation before ic2d begins to integrate. When the voltage applied to its inverting input changes polarity, ic2d integrates at approximately -18.2 V . s-’ (the precise slope depends upon the minimum pulse length from ic4a, and is adjustable using vr3; see ‘setting up’, below). At the end of the 1500 ms period the output of ic2d is at - 15 V and the q output of ic4b goes high. Transistor t l is turned off
+
130
and the output voltage of ic2d returns to + I 2 V. Variable resistances are multi-turn types, in order to provide for accuracy of adjustment. The gain of ic3 is proportional to the current flowing in the bias input, so that as the output of ic2d falls from + 12 to - 15 V, the gain of ic3 falls to zero in a linear fashion. The time after the original stimulus at which ic2d begins to integrate depends upon the duration of the low state at the output of ic4a. If the low state persists for the full 1500 ms, thrn ic2d will not integrate until the train-of-four pulses is complete, and the gain applied to each by ic3 will bc thr samr. As the duration of the low pulse from ic4a becomes shorter, ic2d will be starting to integrate before the train-of-four is complete. The gain applied to the fourth pulse of a train-of-four will then be less than the gain applied to the first pulse, thus setting the train-of-four (TOF) fade ratio (figure 3).
In order to generate the train-of-four envelope it is necessary that ic4a responds only to the first pulse in the train. A high-to-low transition on the input of ic5 causes its output to go high for 3 s. This converts ic4a from the retriggerable to non-retriggerable mode. Repcat stimuli within this period do not intcrferc with envelope function, while the non-retriggerable period is short enough for the device to respond to single twitch frequencies of 0.3 Hz. Switch ‘a’ is incorporated to bypass the envelope function, to allow for stimulator frequencies > 0.3 Hz, and alternative stimulation patterns to TOF.
D. C. Smith
Evoked compound EMG simulator
fourth simulated responses, so that the two responses may be varied independently.
0
1500
Time (ms)
3000
Downloaded by [Australian National University] at 11:04 06 May 2016
Figure 3. Method for generating a train-ofyour f a d e envelope. The four responses to train-ofyour stimulation are represented by the vertical bars. Alteration of the duration of the output pulse of ic4a moves the slope of the integrator, represented by the diagonal line, to the leJ. The gain of ic3 now decreases during the passage of the train-ofyour pulses, so that each pulse in the train exhibits a different amplitude (solid bars).
Setting up The only critical adjustments are those of the slope of integrator ic2d and the pulse widths of monostables ic4a-b. Pulse length at the output of ic4a should be 1500ms at maximum travel of vr2, and is adjusted using vrl. Pulse length at the output of ic4b should be adjusted to 1500 ms, by selection of appropriate timing resistance and capacitor. The minimum pulse width pmin generated by ic4a should then be determined, as should the output voltage span V,,,,, of ic2d. The required integrator slope is then given by V0,,/1500 - pmin.This can be adjusted using vr3.
The output of the simulator circuit is quite stable, and similar to the ECAP recorded during evoked EMG monitoring of neuromuscular transmission during anaesthesia, although the reproducibility of the simulated waveform means that the simulator lacks the momentto-moment variability of the ECAP in vivo. This may eliminate therefore one source of the ‘hunting’ about the control point which is characteristic of feedback control systems. However, stability of the simulated ECAP does allow the estimation of the amount of hunting due to the control system itself. I n practice, the small amount of normal variability is probably unimportant. In situations where accuracy is critical, stored data from real patients may be used to control the simulator. The method which I use is as follows: the Datex Relaxograph neuromuscular transmission monitor produces digital train-of-four response data, available through an RS-232 interface. I n the present application these data are acquired via the RS-423 interface of a BBC microcomputer, and stored on floppy disc. Data can then be read back into the computer at a later date, and output via the 1 MHz external bus connection; synchronization of the output with the stimulus is achieved using the ‘fire’ button connection of the analogue interface in the BBC computer. The analogue control voltage for the simulator is produced by an LMDAC0801 digital-to-analogue convertor and LF356 buffer amplifier. The simulator may thus reproduce any previously recorded neuromuscular response pattern, for use as a teaching aid or as an investigational tool.
Performance The simulator has an extremely stable output, with variation of the simulated ECAP amplitude of < 20.5% over a period of 4 h. This has proved useful for checking the stability and calibration accuracy of commercial and prototype EEMG monitors.
Discussion This simulator provides two facilities not available on the only commercially available EEMG simulator, produced by Datex Instrumentarium for use with their Relaxograph neuromuscular transmission monitor. Completely variable output. The Datex EEMG simulator allows variation of the train-of-four fade ratio, but does not allow simultaneous variation of the amplitude of the first response in the train. External control. The external control capability is useful for teaching of neuromuscular transmission monitoring, and for research into the behaviour of closedloop control systems for muscle relaxant administration during anaesthesia. A microcomputer is used to generate external control signals, in the range +15 to -15 V, which are applied via switch ‘b’ to the bias input of ic3. Although a single voltage source is used, the voltage level is changed during the period between the first and
During the onset of neuromuscular blockade the shape of the ECAP may alter, as a result of a shift in the component harmonics of the ECAP signal towards lower frequencies. Latency (time from stimulus to the start of the initial negative deflection) may change by about 3% and duration of the negative wave may increase by around 13% [4]. Evoked EMG preamplifiers are synchronized with the nerve stimulus to be active only while the ECAP occurs; some 3-4 ms after the stimulus the preamplifier acquires the ECAP signal for a period of approximately 15-20 ms. This is sufficient time to allow for a 3&50% increase in the duration of the ECAP without loss of information, while eliminating movement-related interference [3]. Changes in the duration of the ECAP with the onset of neuromuscular blockade will have less effect on the output from EMG monitors which analyse only the amplitude of the ECAP signal, than on those, such as the Relaxograph, which integrate the amplitude to evaluate the area under the ECAP curve. Since there is some difference between the various neuromuscular blocking drugs in the degree to which the ECAP is prolonged [4], the absence of a facility to modify the duration of the simulated ECAP is not important. However, if this is required, manual control of the duration of the simulator waveform may be achieved by adjusting the time constant of the input resistor and feedback capacitor of the integrator ic2d. Alteration of 131
D. C. Smith Evoked
compound EMG simulator
the input resistor is the easiest option; I found the combination of a 10 kR fixed resistor and a 5 kR variable resistor adequate. Manual control of the latency of the simulated ECAP is achieved by alterating the pulse length of monostable icla.
Acknowledgement
Downloaded by [Australian National University] at 11:04 06 May 2016
I thank Mr J. S. H. Curnow, Principal Biomedical Engineer, Plymouth General Hospital, for his advice during the development of this project. I thank also Mrs Sheila Pattison, medical artist at the Western Infirmary, Glasgow, for the preparation of figure 2. This project was supported by a grant from the Mason Medical Research Foundation.
References 1. GISSEN, A. J. and KATZ,R. L. (1969) Twitch, tetanus and post-tetanic potentiation as indices of nerve-muscle block in man. Anesthesiology, 30, 481-487. 2. ALI, H. H., UTTING,J. E. and GRAY, T. C. (1970) Stimulus frequency in the detection of neuromuscular block in humam. British Journal of Anaesthesia, 42, 967-978. 3. LEE,C., KATZ,R. L., LEE,A. S. J. and GLASER, B. (1977) A new instrument for continuous recording of the evoked compound electromyogram in the clinical setting. Anesthesia and Analgesia, 56, 26C-270. 4. PUGH,N. D., HARPER,N. J. N, HEALY,T. E. J. and PETTS,H . V. (1987) Effects of atracurium and vecuroniurn on the latency and the duration of the negative deflection of the evoked compound action potential of the adductor pollicis. British Journal of Anaesthesia, 59, 195-199.
JOURNAL OF MEDICAL ENGINEERING 8c TECHNOLOGY : AIMS AND SCOPE Published six times a year, the Journal of Medical Engineering 43 Technology (JMET) is an international, independent, multidisciplinary journal promoting an understanding of the physiological processes underlying disease processes and the appropriate application of technology. It is written for and read by scientists, engineers, physicians and surgeons; indeed all those concerned with a practical approach to the application of technology to healthcare. Authors are encouraged to submit articles and papers that are written to inform with a minimum use of jargon and mathematical analysis. Papers published include, principally, those describing: original rcsearch; dcvclopment and evaluation of techniques and devices; reviews discussing progress on a wide range of engineering applied to medicine; and fundamental work using engineering principles to elucidate physiological processes of immediate clinical application. JMET also publishes short reports for rapid communication, contributions on professional aspects of clinical engineering, and correspondence.
All papers are submitted to referees, and the Journal anticipates publishing within 6 months of acceptance of the final manuscript.
JMET also features a comprehensive information service comprising: Selected contents of related journals; summaries of Evalualion (a UK Department of Health publication reporting independent technical and clinical evaluation of a wide range of medical equipment); a comprehensive News, trends & techniques section. Book reviews, a New products section, meetings reports and a meetings calendar completc the package. In keeping with its academic status J M E T is rcvicwed by thc major citation services, and is widely distributcd throughout the world. If you would like to publish your work in the Journal of Medical Engineering & Technology or contribute to the information service, the editor and editorial committee will be pleased to advise. Detailed notes for authors are provided on the inside back cover of every Journal issue.
132
ISSN: 0309-1902 (Print) 1464-522X (Online) Journal homepage: http://www.tandfonline.com/loi/ijmt20
An evoked compound electromyogram simulator with external microprocessor control facility D. C. Smith To cite this article: D. C. Smith (1992) An evoked compound electromyogram simulator with external microprocessor control facility, Journal of Medical Engineering & Technology, 16:3, 129-132, DOI: 10.3109/03091909209021975 To link to this article: http://dx.doi.org/10.3109/03091909209021975
Published online: 09 Jul 2009.
Submit your article to this journal
Article views: 2
View related articles
Full Terms & Conditions of access and use can be found at http://www.tandfonline.com/action/journalInformation?journalCode=ijmt20 Download by: [Australian National University]
Date: 06 May 2016, At: 11:04
Journal of Medical Engineering & Technology, Volume 16, Number 3 (MayIJune 1992), pages 12S132
An evoked compound electromyogram simulator with external microprocessor control facility D. C. Smith?
Downloaded by [Australian National University] at 11:04 06 May 2016
Department of Anaesthesia, Pbmouth General Hospital, Creenbank Terrace, Pbmouth PL4 8QQ UK
A circuit f o r an evoked electromyogram simulator is described, which produces a biphasic triangular waveform similar to the evoked compound action potential seen during clinical quantitative neuromuscular monitoring. The device can produce a fading trainof-fOur sequence, which can be controlled using a single externallyderived voltage. The simulator is useful f o r bench-testing of closed loop muscle relaxant administration systems, and for teaching aspects of neuromuscular monitoring in anaesthesia.
generated 4 ms after each stimulus pulse (figure 1). The delay simulates physiological nerve-muscle conduction time. (3) Output is via a variable-gain buffer amplifier which acts as an envelope shaper. This stage controls the degree of fade, or the decrement in response over time, seen during clinical monitoring of neuromuscular transmission with tctanic or train-of-four stimulation patterns [ 1,2]. T h e simulator output level and fade pattern may be controlled by a single analogue voltage, making it possible to generate the complex onset and offset patterns seen during clinical neuromuscular blockade, or to model a response based upon established pharmacokinetic principles.
Introduction During the development of medical instrumentation systems it is useful to be able to generate signals comparable with those which will be processed in the clinical situation; this allows the designer to investigate the fidelity of reproduction of the applied signal. I n addition, a simulator can act as an ‘artificial patient’ in microprocessor-controlled closed-loop systems, allowing development and testing of such systems to take place in the laboratory, rather than in the clinical situation. The circuit described here has been developed to simulate the cvoked compound muscle action potential (ECAP) observed during the clinical monitoring of neuromuscular transmission by evoked electromyography (EEMG).
Circuit description The circuit is shown in figure 2. Pulses from a physiological nerve stimulator trigger the monostable icla to generate a 4 ms delay pulse, simulating physiological nerve-muscle conduction time. Outputs from icl b then initiate the following functions:
ECAP waveform generator
A low-to-high transition at the input of iclb generates 4.5 ms positive pulses which are applied to a modifi-
A
Design The simulator performs the following functions in response to the output pulses from a physiological nerve stimulator: (1) An optically-isolated trigger input keeps the high voltagc pulses from nerve stimulators out of the simulator circuit. (2) A biphasic, triangular wave of8 ms duration, similar to the physiological compound electromyogram, is 0
2
I
I
4
6
8
I
I
10
12
Time (ms)
?Address for correspondence: Department of Anaesthesia, Western Inznnaiy, Dumbarton Road, Clasgaw C I I GNT. U K
Figure 1. Output waveform produced by the simulator in response to each stimulus pulse f r o m a nerve stimulator. Stimulus pulse occurs at the beginning of the time axis. 129
Downloaded by [Australian National University] at 11:04 06 May 2016
D. C. Smith Evoked compound EMG
icl. ic4 4098 LH32L ic2 k3 CA3080 ic5 TusS5C
simulator
all diodes 1N4148 rxcopl d l 12v ZMW d2 1Sv ZMW
Figure 2. Circuit diagram of the simulator. cation of the simulator circuit described by Lee et al. [3], consisting of ic2a-c. This part of the circuit is a triangular-wave generator, constrained to generate a single cycle in response to each pulse from the nerve stimulator. The simulated ECAP waveform is presented to the transconductance amplifier ic3, where the final amplitude of each simulated ECAP is controlled by an enveloping sequence. Envelope shaping sequence A high-to-low transition at the negative input of monostable ic4a causes its 4 output to go low. Duration of the low state can be varied by vr2 from about 15-1500 ms, the minimum period being determined by the operating characteristics of the 4098 dual monostable. The subsequent return of this output to the high state causes the 4 output of ic4b to go low for 1500 ms. This switches on tl; the collector voltage flips from - 15 to 15 V and remains at + 15 V for 1500 ms (see next section for function of switch ‘a’). The output of ic2d is kept normally at + 12 V by the negative voltage on the input and the action of Zener diodes d l and d2. The Zener diodes ensure that when tl switches there is no delay due to output saturation before ic2d begins to integrate. When the voltage applied to its inverting input changes polarity, ic2d integrates at approximately -18.2 V . s-’ (the precise slope depends upon the minimum pulse length from ic4a, and is adjustable using vr3; see ‘setting up’, below). At the end of the 1500 ms period the output of ic2d is at - 15 V and the q output of ic4b goes high. Transistor t l is turned off
+
130
and the output voltage of ic2d returns to + I 2 V. Variable resistances are multi-turn types, in order to provide for accuracy of adjustment. The gain of ic3 is proportional to the current flowing in the bias input, so that as the output of ic2d falls from + 12 to - 15 V, the gain of ic3 falls to zero in a linear fashion. The time after the original stimulus at which ic2d begins to integrate depends upon the duration of the low state at the output of ic4a. If the low state persists for the full 1500 ms, thrn ic2d will not integrate until the train-of-four pulses is complete, and the gain applied to each by ic3 will bc thr samr. As the duration of the low pulse from ic4a becomes shorter, ic2d will be starting to integrate before the train-of-four is complete. The gain applied to the fourth pulse of a train-of-four will then be less than the gain applied to the first pulse, thus setting the train-of-four (TOF) fade ratio (figure 3).
In order to generate the train-of-four envelope it is necessary that ic4a responds only to the first pulse in the train. A high-to-low transition on the input of ic5 causes its output to go high for 3 s. This converts ic4a from the retriggerable to non-retriggerable mode. Repcat stimuli within this period do not intcrferc with envelope function, while the non-retriggerable period is short enough for the device to respond to single twitch frequencies of 0.3 Hz. Switch ‘a’ is incorporated to bypass the envelope function, to allow for stimulator frequencies > 0.3 Hz, and alternative stimulation patterns to TOF.
D. C. Smith
Evoked compound EMG simulator
fourth simulated responses, so that the two responses may be varied independently.
0
1500
Time (ms)
3000
Downloaded by [Australian National University] at 11:04 06 May 2016
Figure 3. Method for generating a train-ofyour f a d e envelope. The four responses to train-ofyour stimulation are represented by the vertical bars. Alteration of the duration of the output pulse of ic4a moves the slope of the integrator, represented by the diagonal line, to the leJ. The gain of ic3 now decreases during the passage of the train-ofyour pulses, so that each pulse in the train exhibits a different amplitude (solid bars).
Setting up The only critical adjustments are those of the slope of integrator ic2d and the pulse widths of monostables ic4a-b. Pulse length at the output of ic4a should be 1500ms at maximum travel of vr2, and is adjusted using vrl. Pulse length at the output of ic4b should be adjusted to 1500 ms, by selection of appropriate timing resistance and capacitor. The minimum pulse width pmin generated by ic4a should then be determined, as should the output voltage span V,,,,, of ic2d. The required integrator slope is then given by V0,,/1500 - pmin.This can be adjusted using vr3.
The output of the simulator circuit is quite stable, and similar to the ECAP recorded during evoked EMG monitoring of neuromuscular transmission during anaesthesia, although the reproducibility of the simulated waveform means that the simulator lacks the momentto-moment variability of the ECAP in vivo. This may eliminate therefore one source of the ‘hunting’ about the control point which is characteristic of feedback control systems. However, stability of the simulated ECAP does allow the estimation of the amount of hunting due to the control system itself. I n practice, the small amount of normal variability is probably unimportant. In situations where accuracy is critical, stored data from real patients may be used to control the simulator. The method which I use is as follows: the Datex Relaxograph neuromuscular transmission monitor produces digital train-of-four response data, available through an RS-232 interface. I n the present application these data are acquired via the RS-423 interface of a BBC microcomputer, and stored on floppy disc. Data can then be read back into the computer at a later date, and output via the 1 MHz external bus connection; synchronization of the output with the stimulus is achieved using the ‘fire’ button connection of the analogue interface in the BBC computer. The analogue control voltage for the simulator is produced by an LMDAC0801 digital-to-analogue convertor and LF356 buffer amplifier. The simulator may thus reproduce any previously recorded neuromuscular response pattern, for use as a teaching aid or as an investigational tool.
Performance The simulator has an extremely stable output, with variation of the simulated ECAP amplitude of < 20.5% over a period of 4 h. This has proved useful for checking the stability and calibration accuracy of commercial and prototype EEMG monitors.
Discussion This simulator provides two facilities not available on the only commercially available EEMG simulator, produced by Datex Instrumentarium for use with their Relaxograph neuromuscular transmission monitor. Completely variable output. The Datex EEMG simulator allows variation of the train-of-four fade ratio, but does not allow simultaneous variation of the amplitude of the first response in the train. External control. The external control capability is useful for teaching of neuromuscular transmission monitoring, and for research into the behaviour of closedloop control systems for muscle relaxant administration during anaesthesia. A microcomputer is used to generate external control signals, in the range +15 to -15 V, which are applied via switch ‘b’ to the bias input of ic3. Although a single voltage source is used, the voltage level is changed during the period between the first and
During the onset of neuromuscular blockade the shape of the ECAP may alter, as a result of a shift in the component harmonics of the ECAP signal towards lower frequencies. Latency (time from stimulus to the start of the initial negative deflection) may change by about 3% and duration of the negative wave may increase by around 13% [4]. Evoked EMG preamplifiers are synchronized with the nerve stimulus to be active only while the ECAP occurs; some 3-4 ms after the stimulus the preamplifier acquires the ECAP signal for a period of approximately 15-20 ms. This is sufficient time to allow for a 3&50% increase in the duration of the ECAP without loss of information, while eliminating movement-related interference [3]. Changes in the duration of the ECAP with the onset of neuromuscular blockade will have less effect on the output from EMG monitors which analyse only the amplitude of the ECAP signal, than on those, such as the Relaxograph, which integrate the amplitude to evaluate the area under the ECAP curve. Since there is some difference between the various neuromuscular blocking drugs in the degree to which the ECAP is prolonged [4], the absence of a facility to modify the duration of the simulated ECAP is not important. However, if this is required, manual control of the duration of the simulator waveform may be achieved by adjusting the time constant of the input resistor and feedback capacitor of the integrator ic2d. Alteration of 131
D. C. Smith Evoked
compound EMG simulator
the input resistor is the easiest option; I found the combination of a 10 kR fixed resistor and a 5 kR variable resistor adequate. Manual control of the latency of the simulated ECAP is achieved by alterating the pulse length of monostable icla.
Acknowledgement
Downloaded by [Australian National University] at 11:04 06 May 2016
I thank Mr J. S. H. Curnow, Principal Biomedical Engineer, Plymouth General Hospital, for his advice during the development of this project. I thank also Mrs Sheila Pattison, medical artist at the Western Infirmary, Glasgow, for the preparation of figure 2. This project was supported by a grant from the Mason Medical Research Foundation.
References 1. GISSEN, A. J. and KATZ,R. L. (1969) Twitch, tetanus and post-tetanic potentiation as indices of nerve-muscle block in man. Anesthesiology, 30, 481-487. 2. ALI, H. H., UTTING,J. E. and GRAY, T. C. (1970) Stimulus frequency in the detection of neuromuscular block in humam. British Journal of Anaesthesia, 42, 967-978. 3. LEE,C., KATZ,R. L., LEE,A. S. J. and GLASER, B. (1977) A new instrument for continuous recording of the evoked compound electromyogram in the clinical setting. Anesthesia and Analgesia, 56, 26C-270. 4. PUGH,N. D., HARPER,N. J. N, HEALY,T. E. J. and PETTS,H . V. (1987) Effects of atracurium and vecuroniurn on the latency and the duration of the negative deflection of the evoked compound action potential of the adductor pollicis. British Journal of Anaesthesia, 59, 195-199.
JOURNAL OF MEDICAL ENGINEERING 8c TECHNOLOGY : AIMS AND SCOPE Published six times a year, the Journal of Medical Engineering 43 Technology (JMET) is an international, independent, multidisciplinary journal promoting an understanding of the physiological processes underlying disease processes and the appropriate application of technology. It is written for and read by scientists, engineers, physicians and surgeons; indeed all those concerned with a practical approach to the application of technology to healthcare. Authors are encouraged to submit articles and papers that are written to inform with a minimum use of jargon and mathematical analysis. Papers published include, principally, those describing: original rcsearch; dcvclopment and evaluation of techniques and devices; reviews discussing progress on a wide range of engineering applied to medicine; and fundamental work using engineering principles to elucidate physiological processes of immediate clinical application. JMET also publishes short reports for rapid communication, contributions on professional aspects of clinical engineering, and correspondence.
All papers are submitted to referees, and the Journal anticipates publishing within 6 months of acceptance of the final manuscript.
JMET also features a comprehensive information service comprising: Selected contents of related journals; summaries of Evalualion (a UK Department of Health publication reporting independent technical and clinical evaluation of a wide range of medical equipment); a comprehensive News, trends & techniques section. Book reviews, a New products section, meetings reports and a meetings calendar completc the package. In keeping with its academic status J M E T is rcvicwed by thc major citation services, and is widely distributcd throughout the world. If you would like to publish your work in the Journal of Medical Engineering & Technology or contribute to the information service, the editor and editorial committee will be pleased to advise. Detailed notes for authors are provided on the inside back cover of every Journal issue.
132
