IEEE TRANSACTIONS ON BIOMEDICAL ENGINEERING, MARCH 1976
160
methods in order to obtain high frequent components present in the QRS complex. For instance averaging of "slurs and notches" [41, [5]. c. Also averaging of the complete ECG will be possible. This enables non-invasive investigations on the conduction system of the heart to be carried out [61. ACKNOWLEDGMENT The authors are very grateful to Mr. J. G. Meijer of the Department of Physiology for the photographic assistance in the preparation of the illustrations. They also wish to thank Mrs. W. M. U. van Barschot for the accurate typing of the manuscript.
REFERENCES [1] W. P. Holsinger, K. M. Kempner and M. H. Miller. A QRS preprocessor based on digital differentiation. IEEE Trans. Biomed. Eng., vol. BME-18, nr. 3, pp. 212-217, May 1971. [2] A. R. Hambley, R. L. Moruzzi and C. L. Feldman. The use of intrinsic components in an ECG filter. IEEE Trans. Bionm Eng., vol. BME-21, nr. 6, pp. 469-473, November 1974. [3] A. Sandman, D. W. Hill and A. H. Wilcock. Analogue preprocessor for the measurement by a digital computer of R-R intervals and R wave widths. Med. Biol. Eng., vol. 11, nr. 2, pp. 191200, March 1973. [4] N. C. Flowers and L. G. Horan. Diagnostic impact of QRS notching in high-frequency electrocardiograms of living subjects with heart disease. Circulation, vol. XLIV, pp. 605-611, October 1971. [5] P. H. Langner, D. B. Geselowitz and S. A. Briller. Wide band recording of the electrocardiogram and coronary heart disease. An. Heart Journ., vol. 86, nr. 3, pp. 308-317, September 1973. [6] E. J. Berbari, R. Lazarra, P. Samet and B. J. Scherlag. Noninvasive technique for detection of electrical activity during the P-R segment. Circulation, vol. XLVIII, pp. 1005-1013, November 1973.
An Interactive Computer Peripheral to Measure the Electromyographic Silent Period S. S. ALTUG, C. T. CHILDRESS, JR., S. M. DEMUND, W. D. McCALL, JR., MEMBER, IEEE, AND M. M. ASH, JR. Abstract-A device to provide automated measurement of the electromyographic silent period with real time capability uflizing a voltagetime window is described. This device is being used in the clinical dental diagnosis and treatment of functional disorders of the masticatory system. The design, performance, utilization, and other applications of this device are discussed.
INTRODUCTION Controversy abounds in clinical dentistry over the nomenclature, etiology [1]-[4], and treatment [5]-[9] of pain associated with the muscles of mastication and the temporomandibular joint (TMJ). DeBoever [10] has reviewed these controversies while Agerberg and Carlsson [ 11 ] have reported epidemiological evidence that up to 57 percent of the adult population report one or more symptoms of TMJ dysfunction Manuscript received October 22, 1974; revised April 25, 1975. This work was supported by the USPHS under Grant DE 02731. The authors are with the Bioengineering and Occlusion aboratory, Department of Occlusion, Dental Research Institute, School of Dentistry, University of Michigan, Ann Arbor, MI 48104.
and about 12 percent of the population report pain on jaw opening. This syndrome appears to be a problem of some complexity, and therefore a quantitative diagnosis would be valuable in assessing symptom severity, treatment progress, and competing treatment plans. Our laboratory has taken a multi-faceted approach to the problem of quantifying the diagnosis of TMJ problems [ 12] [15]. The goal is to improve the curative and preventive techniques of the dentist by providing quantitative measurements for diagnosis. One quantitative measurement technique reported to have diagnostic significance is the duration of the electromyographic (EMG) silent period following the jaw-jerk or myotatic reflex. Bessette, Bishop, and Mohl [ 16] have reported that the silent period duration is greater than 32 ms in diagnosed TMJ patients and less than 28 ms in asymptomatic patients. Further, they report that successful treatment results in a decrease of the silent period duration to within the normal range [16]. Studies from our laboratory have confirmed and extended these results [14], [15]. Previous techniques for measuring the duration of the silent period whether using a mechanical device [ 16], optical scanner [17], or photographic projection [18] all involve slow, postexperiment hand measurements with the attendant possibilities for bias and error. The importance of the phenomena, the number of measurements required, and the possibility of human error all suggest that a rapid, automated technique for measuring silent period duration would significantly enhance research progress. The purpose here is to describe a device that implements such a technique. A preliminary report has been presented [19].
DESIGN CONSIDERATIONS Input Signal Constraints: While physiologically the silent period is comprised of a complex interaction of disfacilitation and inhibition at the motoneuron, operationally a simple definition must be used. Experience suggested that a definition including both an amplitude criterion and duration criterion would be satisfactory. An amplitude window is necessary because noise in the recording system precludes an absolutely "silent" silent period. A time window, constraining the duration of acceptable silent periods to within reference minimum and maximum durations, is necessary to exclude zero crossings and other short periods of low activity on the minimum side and rest and other periods of low activity on the maximum side. Even with the two windows, some parts of EMG traces were expected to fit the operational definition of the silent period and cause false alarms, so a monitoring technique would be necessary. This would retain the clinical judgement of the clinician as to what constituted a silent period while relieving him of the measurement chore. The intent is not to replace the dentist but to relieve him of non-clinically oriented tasks. Another feature of the EMG signal is variability of signal and noise amplitude from patient to patient. Hence the ability to control the windows was considered necessary. Variations on the order of milliseconds were expected from the nature of the waveform as the EMG signal entered and left the silent period. Therefore device accuracy on the order of ± 1 percent was considered adequate. This would amount to ± 80 Mus for the shortest silent period expected. The EMG signal has a spectrum that extends to a few hundred Hz but most of the power is concentrated between 30 and 100 Hz [201, [211. Hence commercially available devices would give adequate frequency response. Laboratory Environment: This design must interface to other items of laboratory equipment. The flow of information is shown in Fig. 1. The EMG amplifiers and polygraph were
161
COMMUNICATIONS
Fig. 1. Flow of information. The EMG data streams from the muscles of mastication are amplified (Grass Model 78 polygraph, 30 to 30 kHz, with Model 7P511 amplifiers, 0-90 Hz for pens), displayed, and recorded on analog magnetic tape (Hewlett-Packard Model 3955, FM, 30 in/sec). Upon replay at four to one speed reduction, each data stream is processed by the silent period peripheral. Timing and display capability is provided by the device, while the computer provides interactive control and storage facilities.
Fig. 2. System block diagram of device. The analog signal is converted to logic levels according to whether it is or is not within the amplitude window. This signal may then enable a ripple counter to measure duration by counting clock pulses. At the cessation of a silent period, control circuitry transfers the duration, through the interface, to the computer's I/O bus.
available, so the output of the pen driver amplifiers would be the input to the device and an unused polygraph channel could be used as an output to monitor silent period detection. In addition to the polygraph, a PDP 8/S digital computer was available with teletype, digital magnetic tape, and 8k words of memory but without a real time clock or digital-to-analog converter. The peripheral device would need to contain the latter two items. Since the device was to interconnect between separate pieces of laboratory equipment while deriving its power from the computer power supplies, high noise immunity and low power drain would be desirable features. While low-power TTL logic would probably suffice, the CMOS logic family was selected for its high noise immunity. The silent period durations were expected to be in the range from 8 to 200 ms. These durations, together with the 12 bit word length of the computer and the desire for one percent accuracy, constrained the clock period to be between 50 and 80 ,s. A period of 64 microseconds was selected for ease in software conversion from clock counts to milliseconds. These design considerations led to the block diagram shown in Fig. 2. The "analog-to-logical" converter would implement the voltage window, the device control unit would implement the time window, and the clock with the ripple counter would record the silent period.
CIRCUIT DESCRIPTION The analog and digital circuits implementing the device are shown in Fig. 3. A digital clock was fabricated such that the period could be adjusted to 64 microseconds. This clock was found to have satisfactory stability for the present application. Upon redesign, however, a crystal controlled clock should be implemented for improved accuracy and stability. The amplitude portion of the silent period definition is fulfilled by the "analog-to-logical" converter. This converter is a one-bit, rather than a multi-bit, analog-to-digital converter that provides continuous, rather than sampled, conversion and two, rather than one, voltage thresholds. The output of the NAND gate is false only when the input EMG signal is less than the high threshold and more than the low threshold. The length of the silent period is measured by counting clock pulses with a ripple counter. The enabling, disabling, and resetting of this counter will be considered for three cases of silent period duration: (1) less than 8 ms, (2) between 8 and 200 ms., and (3) greater than 200 ms. A timing diagram, illustrating the three cases, is given in Fig. 4. Assuming the ripple counter to be reset, counting is enabled by the INSIDE signal. Counting may be disabled in one of two ways: The EMG leaves the amplitude window and the INSIDE signal disables counting (cases 1 and 2) or the count reaches octal 6000 (196 ms, case 3) and the STOP signal disables further counting. As soon as the minimum period is reached the PERIOD SENSOR flip flop is set and the PERIOD INDICATE OUTPUT goes high. This provides the comparision signal for the operator. In case 1, the PERIOD SENSOR flip flop is reset and that signal, together with the output of the analog to logical converter indicating that the EMG has left the voltage window, is sufficient to RESET the counter. In cases 2 and 3 the PERIOD SENSOR is set so the resetting occurs after the transfer has been completed. Transfer of data from the ripple counter to the accumulator of the PDP 8/S is initiated by the interrupt (INT) signal. This occurs when the PERIOD SENSOR has been set and the input signal leaves the window, thus data is not transferred for the case of "silent periods" under 8 ms. In addition to the logic circuit shown in Fig. 3, level converters were fabricated to interface the CMOS logic levels of the peripheral device to the DTL logic levels of the computer. PERFORMANCE
The repeatability and accuracy of any device are important performance parameters. Results were obtained both for one sample of EMG data, repeated 20 times through the device, to demonstrate source and device error combined, and for a constant known pulsewidth applied to the device, to demonstrate device error only. The results of the first test show that 95 percent of the measured silent periods were within ± 2.2 ms of the average length (See Table I). To eliminate the variability of analog tape speed, a second test was performed utilizing a constant pulsewidth from a signal generator. The results showed that the measured times are within ± 0.2 ms of the average at the 95 percent level of confidence, well within the design constraint (See Table II). The use of voltage thresholds for detection presupposes that the silent period is mainly a function of amplitude: this device also requires that the signal remain within this band for a minimal amount of time in order to be detected. With these assumptions, this device is somewhat limited as to the kind of signal variations it can detect. If a silent period occurs in the EMG with a rather slow decay of voltage level into the defined threshold levels, then it is very likely that the period will be
IEEE TRANSACTIONS ON BIOMEDICAL ENGINEERING, MARCH 1976
162
ANALOG TO LOGICAL CONVERTER
Fig. 3. Detailed logic circuit. This circuit provides a hardware realization of the silent period definition and implements the block diagram of Fig. 2. Not shown are level converters to interface the CMOS logic levels of this device to the DTL logic levels of the computer. A detailed explanation of the operation is provided in the text. The components used are as follows: D flip-flops: MC 14013; J-K flip-flops: MC 14027; counter: MC 14040; 6-input AND: MC 14501; 3-input NAND: MC 14023; 2-input NAND: MC 14011; inverters: MC 14009; and operational amplifiers: 741C.
.I!N.
EMG CASE 3
I/I-
-
CASE 1
CASE 2
INSIDE PD SENSOR BIT I BIT 0 (msb)1
1
I /'I,-
_
TABLE I DEVICE PERFORMANCE FOR TYPICAL EMG SIGNAL Minimum
Duration 81.856 ms
Maximum Duration 83.008 ms
Duration 82.531 ms
Standard Deviation 0.380 ms
20
2
46.656
51.072
47.603
1.181
20
3
67.840
69.056
68.592
0.314
20
4
73.664
74.752
74.429
0.354
20
5
73.215
74.816
74.432
0.497
20
Silent Period Number 1
Mean
N
STOPIIII READY INT
lop IOP 24
IOP4 RESET
TABLE II ''
,n
n
u VI
n
I
f
Fig. 4. Logic timing. Schematic rendering of the logic sequence for each of the three cases that implement the time window. Long times are shown dotted. For example, in case 2, the PD SENSOR goes high 8 milliseconds after INSIDE goes low, and returns low several microseconds after INSIDE goes high.
undetected or incorrectly measured. Experience with measuring silent periods from dozens of patients indicated that this occurs occasionally. Most other methods [151-[17] presently in use have time measurement errors much larger than the present device
because of limitations of the graphical recorders and the human error of determining when a silent period begins and ends. The method reported here minimizes the human measurement error and is constrained by device measurement error
Device Performance for Constant Pulse Width Input Input Pulse Width 30.600 ms
Minimum Duration 30.464 ms
Maximum Duration 30.720 ms
Duration 30.639 ms
40.000
39.872
40.192
40.056
Mean
Standard
N
Deviation 0.098 ms
50
0.103
50
only. The device error is also constant with respect to time and input signal variation. Additionally, this device has the capability of measuring silent periods in a real time environment, where previous methods are restricted to first recording the data graphically and then measuring the silent period. CLINICAL UTILIZATION Measurement Process: Operation of the device on typical data is shown in Fig. 5. The procedure used to measure the silent period duration is as follows. (1) Threshold voltages are determined from the EMG tracing for the channel selected and adjusted on the device. (2) All devices are started. (3) Calculations are initiated at the end of the sample by typing a
COMMUNICATIONS
163
RIGHT ANTERIOR TEMPORAL
LEFT
ASILENT
PERIOD
RIGHT MASSETER LEFT MASSETER
DIGASTRIC
JAW JERKS
F
5
0ml e 500 me
\
1
-
PERIOD SENSOR
Fig. 5. Typical data. The upper traces show the input EMG traces from five different masticatory muscles. The seventh trace gives the output of the peripheral used for verification of the existence of the silent period. The lowest trace is a timing marker. In this example the silent periods from the right masseter muscle are being measured.
character on the teletype keyboard. (4) The ordinal numbers of the desired silent periods are entered via the teletype. (5) The durations of the selected silent periods are printed at the teletype and optionally transferred to storage for later analysis.
CLINICAL RESULTS While the purpose of this communication is to describe the measuring device, some discussion of the use of silent period duration measurements is appropriate. DeBoever and Kovaleski [22] found that the number of silent periods decreased upon insertion of the occlusal bite plane splint (a recommended treatment in TMJ problems) but the duration of the remaining silent periods were not significantly changed. Beemsterboer et al. [14] examined the effect of the splint on the silent period duration after both the jaw-jerk and the openclose-clench cycle. The durations after treatment with the occlusal splint decreased significantly for the jaw-jerk technique. Surprisingly, they found further that immediately after the insertion of the splint the duration of the silent period fell to within the normal range. In these studies, however, numerous factors were uncontrolled and, as a result of the success of the above studies, McNamara et al. [15] undertook to examine some of these factors. Biting force, for example, was found to influence the duration: a decrease in duration was found with an increase in biting force. Another parameter, the angle at which the jawjerk taps are applied did not cause a statistically significant change in silent period duration. A third parameter, muscle length, also did not influence durations significantly. Software Support: The computer program associated with this device interactively controls the data acquisition and
processing by prompting the operator for documentation and receiving commands from the operator at the teletype.' After initiating measurements from the computer console, the following are carried out via the teletype control: A termination character ends the processing of silent periods. Documentation is requested as to patient, data, muscle, and other clinically relevant parameters for storage along with silent period durations. The ordinal numbers of the "true" silent periods are requested, and upon termination, the duration of each in milliseconds is printed. Optionally the documentation and durations may be stored on magnetic tape or punched on paper tape. CONCLUSIONS The advantages of the described device in processing electromyographic silent periods are manifold. The process with its on-line capability is faster than manual techniques, formatted hard copy is provided, human measurement error is eliminated, a consistent silent period definition is implemented, and the dental personnel are relieved of an ancillary task. The disadvantages are that the powerful pattern recognition powers of the human cannot be used to recognize out-of-definition silent periods or silent periods with a low signal-to-noise ratio. Thus a small fraction of the silent periods are still measured manually. Since the computer is used basically for pulse generator and data storage medium, this system could easily be extended to processing multiple channels simultaneously by constructing more peripherals with different device addresses. The basic
1Available on request from the authors.
IEEE TRANSACTIONS ON BIOMEDICAL ENGINEERING, MARCH 1976
164
device could also be altered to provide a self contained tool for portable clinical use. By altering the "analog-to-logical" converter, or the logical feedback from the counter, or both, many different voltagetime windows could be implemented and thus provide other applications for this device where event and timing applications are of interest. The investigations described above illustrate some of the uses of this device in the diagnosis and treatment of temporomandibular joint disturbances and indicate that the silent period has proved to be an interesting and useful diagnostic sign to enhance research intQ the controversial etiology and treatment of these disturbances. REFERENCES
[11 L. L. Schwartz, "A temporomandibular joint pain-dysfunction syndrome," J. Chron. Dis., vol. 3, pp. 284-293, 1956. [2] C. S. Greene and D. M. Laskin, "Splint therapy for the myofacial [3]
[4] [5]
[61 [7]
[8]
[9] [10] [11]
[12]
[13]
[14] [15]
[161 [17] [18] [19]
[20]
pain-dysfunction syndrome: a comparative study," J. Am. Dent. Assoc., vol. 84, pp. 624-628, 1962. C. Molin, "Studies in mandibular pain dysfunction syndrome," Swed. Dent. J., vol. 66 (suppl. 4), pp. 1-55, 1973. D. A. Kerr, "The pathology of traumatic temporomandibular arthritis produced by traumatic occlusion," J. Dent. Med., vol. 12, pp. 190-192, 1957. L. Schwartz and D. P. Tausig, "Temporomandibular joint paintreatment with intramuscular infiltration of tetracaine hydrochloride: A preliminary report," N. Y. Dent. J., vol. 20, pp. 219223, 1954. I. Yavelow, I. Forster, and M. Wininger, "Mandibular relearning," Oral Surgery, vol. 36, pp. 632-641, 1973. L. Schwartz, "Temporomandibular joint syndromes," J. Pros. Dent., vol. 7, pp. 489-499, 1957. S. P. Ramfjord and M. M. Ash, Occlusion. Philadelphia: Saunders, 1966, pp. 248-287. P. Goodman and C. S. Greene, "Response to placebo equilibration in MPD patients," Proc. Inter. Assoc. Dent. Res., vol. 52, p. 72 (abst.), 1973. J. A. DeBoever, "Functional disturbances of the temporomandibular joints," Oral Sciences Reviews, vol. 2, pp. 100-117, 1973. Agerberg and G. E. Carlsson, "Functional disorders of the masticatory system. I. Distribution of symptoms according to age and sex as judged from investigation by questionaire," Acta. Odont. Scand., vol. 30, pp. 597-613, 1972. W. D. McCall, Jr., P. F. Crane, D. C. McNamara, and M. M. Ash, Jr., "Phase plane analysis of jaw motion in functional TMJ disturbances," Proc. Inter. Assoc. Dent. Res., vol. 53, p. 173 (abst.), 1974. D. C. McNamara, P. F. Crane, W. D. McCall, Jr., and M. M. Ash, Jr., "Diagnostic implication of the occlusal velocity envelope of motion," Proc. Inter. Assoc. Dent. Res., vol. 53, p. 169 (abst.), 1974. P. Beemsterboer, D. C. McNamara, S. Holden, and M. M. Ash, Jr., "Effect of bite plane splint on EMG silent period duration," Proc. Inter. Assoc. Dent. Res., vol. 53, p. 169 (abst), 1974. D. C. McNamara, P. F. Crane, W. D. McCall, Jr., and M. M. Ash, Jr., "Myotatic reflex response to unloading and loading jaw-jerk stimulation," Proc. Inter. Assoc. Dent. Res., vol. 53, p. 205 (abst.), 1974. R. Bessette, B. Bishop, and N. Mohl, "Duration of masseteric silent period in patients with TMJ syndrome," J. AppL Physiol., vol. 30, pp. 864-869, 1971. H. S. Brenman, M. A. Black, and J. G. Coslet, "Interrelationship between the electromyographic silent period and dental occlusion," J. Dent. Res., vol. 47, p. 502, 1968. D. E. Beaudreau, W. F. Daugherty, and W. S. Masland, "Two types of motor pause in masticatory spindles," Am. J. Physiol., vol. 216, pp. 16-21, 1969. S. S. Altug, C. T. Childress, S. DeMund, and W. D. McCall, Jr., "An interactive computer peripheral to measure the electromyographic silent period," Proc. Inter. Assoc. Dent. Res., vol. 53, p. 202 (abst.), 1974. K. J. Hayes, "Wave analysis of tissue noise and muscle action potentials," J. AppL Physiol., vol. 15, pp. 749-750, 1960.
[21] E. Kwatny, D. H. Thomas, and H. G. Kwatny, "An application of signal processing techniques to the study of myoelectric signals," IEEE Trans. Biomed. Engr., vol. BME-17, pp. 303-312, 1970. [22] J. DeBoever and W. C. Kovaleski, III, "Occlusal splints: Effect on musculature of TMJ dysfunction patients, Proc. Inter. Assoc. Dent. Res., vol. 52, p. 169 (abst.), 1974.
Neural Control of Heart Rate: A Conciliation of Models PETER G. KATONA, MEMBER, IEEE, PAUL J. MARTIN, AND FELIX JIH Abstract-Two published models for the interaction of sympathetic and parasympathetic effects on heart rate are examined. The models appear to support contradictory conclusions: one was interpreted to imply no interaction, while the other one was said to indicate significant interaction between the two types of autonomic controls. It is shown that the two models are essentially equivalent, and that the different conclusions are due to different interpretations of the concept of interaction.
INTRODUCTION It is well known that the heart is under the dual control of the sympathetic and parasympathetic autonomic nervous systems. In an attempt to characterize the interaction between parasympathetic and sympathetic neural stimulation Rosenblueth and Simeone [1 ] developed a mathematical model to describe the steady-state effects of sympathetic. parasympathetic and combined sympathetic and parasympathetic electrical stimulation on heart rate. They concluded that the two types of stimuli exerted their effects independently of each other since the percentage change of heart rate caused by a particular frequency of sympathetic (or parasympathetic) stimulation was the same regardless of the background level of parasympathetic (or sympathetic) stimulation. More recently, Warner and Russell [21 presented another model for combined parasympathetic and sympathetic influences on heart rate, but they concluded that the sympathetic and parasympathetic influences interact rather than act
independently. Resolving the apparent discrepancy is desirable for at least two reasons. First, modeling is supposed to increase physiological understanding, and if two different conclusions are drawn from two different models describing the same system, a resolution of the discrepancy is a prerequisite for furthering a physiological understanding of the system in question. Second, recent reports indicate that cardiac disease may be associated with abnormal parasympathetic control, and that parasympathetic stimulation appears to have beneficial effects during acute myocardial ischemia [31, [4]. It thus appears that an assessment of the degree of parasympathetic cardiac control may be clinically desirable. Such an assessment must be based on an understanding of the interaction of sympa-
Manuscript received March 4, 1975; revised May 27, 1975, and June 24, 1975. This work was supported in part by the National Institutes
of Health under Grant GM-19599. The authors are with the Department of Biomedical Engineering, Case Western Reserve University, Cleveland, OH 44106.
160
methods in order to obtain high frequent components present in the QRS complex. For instance averaging of "slurs and notches" [41, [5]. c. Also averaging of the complete ECG will be possible. This enables non-invasive investigations on the conduction system of the heart to be carried out [61. ACKNOWLEDGMENT The authors are very grateful to Mr. J. G. Meijer of the Department of Physiology for the photographic assistance in the preparation of the illustrations. They also wish to thank Mrs. W. M. U. van Barschot for the accurate typing of the manuscript.
REFERENCES [1] W. P. Holsinger, K. M. Kempner and M. H. Miller. A QRS preprocessor based on digital differentiation. IEEE Trans. Biomed. Eng., vol. BME-18, nr. 3, pp. 212-217, May 1971. [2] A. R. Hambley, R. L. Moruzzi and C. L. Feldman. The use of intrinsic components in an ECG filter. IEEE Trans. Bionm Eng., vol. BME-21, nr. 6, pp. 469-473, November 1974. [3] A. Sandman, D. W. Hill and A. H. Wilcock. Analogue preprocessor for the measurement by a digital computer of R-R intervals and R wave widths. Med. Biol. Eng., vol. 11, nr. 2, pp. 191200, March 1973. [4] N. C. Flowers and L. G. Horan. Diagnostic impact of QRS notching in high-frequency electrocardiograms of living subjects with heart disease. Circulation, vol. XLIV, pp. 605-611, October 1971. [5] P. H. Langner, D. B. Geselowitz and S. A. Briller. Wide band recording of the electrocardiogram and coronary heart disease. An. Heart Journ., vol. 86, nr. 3, pp. 308-317, September 1973. [6] E. J. Berbari, R. Lazarra, P. Samet and B. J. Scherlag. Noninvasive technique for detection of electrical activity during the P-R segment. Circulation, vol. XLVIII, pp. 1005-1013, November 1973.
An Interactive Computer Peripheral to Measure the Electromyographic Silent Period S. S. ALTUG, C. T. CHILDRESS, JR., S. M. DEMUND, W. D. McCALL, JR., MEMBER, IEEE, AND M. M. ASH, JR. Abstract-A device to provide automated measurement of the electromyographic silent period with real time capability uflizing a voltagetime window is described. This device is being used in the clinical dental diagnosis and treatment of functional disorders of the masticatory system. The design, performance, utilization, and other applications of this device are discussed.
INTRODUCTION Controversy abounds in clinical dentistry over the nomenclature, etiology [1]-[4], and treatment [5]-[9] of pain associated with the muscles of mastication and the temporomandibular joint (TMJ). DeBoever [10] has reviewed these controversies while Agerberg and Carlsson [ 11 ] have reported epidemiological evidence that up to 57 percent of the adult population report one or more symptoms of TMJ dysfunction Manuscript received October 22, 1974; revised April 25, 1975. This work was supported by the USPHS under Grant DE 02731. The authors are with the Bioengineering and Occlusion aboratory, Department of Occlusion, Dental Research Institute, School of Dentistry, University of Michigan, Ann Arbor, MI 48104.
and about 12 percent of the population report pain on jaw opening. This syndrome appears to be a problem of some complexity, and therefore a quantitative diagnosis would be valuable in assessing symptom severity, treatment progress, and competing treatment plans. Our laboratory has taken a multi-faceted approach to the problem of quantifying the diagnosis of TMJ problems [ 12] [15]. The goal is to improve the curative and preventive techniques of the dentist by providing quantitative measurements for diagnosis. One quantitative measurement technique reported to have diagnostic significance is the duration of the electromyographic (EMG) silent period following the jaw-jerk or myotatic reflex. Bessette, Bishop, and Mohl [ 16] have reported that the silent period duration is greater than 32 ms in diagnosed TMJ patients and less than 28 ms in asymptomatic patients. Further, they report that successful treatment results in a decrease of the silent period duration to within the normal range [16]. Studies from our laboratory have confirmed and extended these results [14], [15]. Previous techniques for measuring the duration of the silent period whether using a mechanical device [ 16], optical scanner [17], or photographic projection [18] all involve slow, postexperiment hand measurements with the attendant possibilities for bias and error. The importance of the phenomena, the number of measurements required, and the possibility of human error all suggest that a rapid, automated technique for measuring silent period duration would significantly enhance research progress. The purpose here is to describe a device that implements such a technique. A preliminary report has been presented [19].
DESIGN CONSIDERATIONS Input Signal Constraints: While physiologically the silent period is comprised of a complex interaction of disfacilitation and inhibition at the motoneuron, operationally a simple definition must be used. Experience suggested that a definition including both an amplitude criterion and duration criterion would be satisfactory. An amplitude window is necessary because noise in the recording system precludes an absolutely "silent" silent period. A time window, constraining the duration of acceptable silent periods to within reference minimum and maximum durations, is necessary to exclude zero crossings and other short periods of low activity on the minimum side and rest and other periods of low activity on the maximum side. Even with the two windows, some parts of EMG traces were expected to fit the operational definition of the silent period and cause false alarms, so a monitoring technique would be necessary. This would retain the clinical judgement of the clinician as to what constituted a silent period while relieving him of the measurement chore. The intent is not to replace the dentist but to relieve him of non-clinically oriented tasks. Another feature of the EMG signal is variability of signal and noise amplitude from patient to patient. Hence the ability to control the windows was considered necessary. Variations on the order of milliseconds were expected from the nature of the waveform as the EMG signal entered and left the silent period. Therefore device accuracy on the order of ± 1 percent was considered adequate. This would amount to ± 80 Mus for the shortest silent period expected. The EMG signal has a spectrum that extends to a few hundred Hz but most of the power is concentrated between 30 and 100 Hz [201, [211. Hence commercially available devices would give adequate frequency response. Laboratory Environment: This design must interface to other items of laboratory equipment. The flow of information is shown in Fig. 1. The EMG amplifiers and polygraph were
161
COMMUNICATIONS
Fig. 1. Flow of information. The EMG data streams from the muscles of mastication are amplified (Grass Model 78 polygraph, 30 to 30 kHz, with Model 7P511 amplifiers, 0-90 Hz for pens), displayed, and recorded on analog magnetic tape (Hewlett-Packard Model 3955, FM, 30 in/sec). Upon replay at four to one speed reduction, each data stream is processed by the silent period peripheral. Timing and display capability is provided by the device, while the computer provides interactive control and storage facilities.
Fig. 2. System block diagram of device. The analog signal is converted to logic levels according to whether it is or is not within the amplitude window. This signal may then enable a ripple counter to measure duration by counting clock pulses. At the cessation of a silent period, control circuitry transfers the duration, through the interface, to the computer's I/O bus.
available, so the output of the pen driver amplifiers would be the input to the device and an unused polygraph channel could be used as an output to monitor silent period detection. In addition to the polygraph, a PDP 8/S digital computer was available with teletype, digital magnetic tape, and 8k words of memory but without a real time clock or digital-to-analog converter. The peripheral device would need to contain the latter two items. Since the device was to interconnect between separate pieces of laboratory equipment while deriving its power from the computer power supplies, high noise immunity and low power drain would be desirable features. While low-power TTL logic would probably suffice, the CMOS logic family was selected for its high noise immunity. The silent period durations were expected to be in the range from 8 to 200 ms. These durations, together with the 12 bit word length of the computer and the desire for one percent accuracy, constrained the clock period to be between 50 and 80 ,s. A period of 64 microseconds was selected for ease in software conversion from clock counts to milliseconds. These design considerations led to the block diagram shown in Fig. 2. The "analog-to-logical" converter would implement the voltage window, the device control unit would implement the time window, and the clock with the ripple counter would record the silent period.
CIRCUIT DESCRIPTION The analog and digital circuits implementing the device are shown in Fig. 3. A digital clock was fabricated such that the period could be adjusted to 64 microseconds. This clock was found to have satisfactory stability for the present application. Upon redesign, however, a crystal controlled clock should be implemented for improved accuracy and stability. The amplitude portion of the silent period definition is fulfilled by the "analog-to-logical" converter. This converter is a one-bit, rather than a multi-bit, analog-to-digital converter that provides continuous, rather than sampled, conversion and two, rather than one, voltage thresholds. The output of the NAND gate is false only when the input EMG signal is less than the high threshold and more than the low threshold. The length of the silent period is measured by counting clock pulses with a ripple counter. The enabling, disabling, and resetting of this counter will be considered for three cases of silent period duration: (1) less than 8 ms, (2) between 8 and 200 ms., and (3) greater than 200 ms. A timing diagram, illustrating the three cases, is given in Fig. 4. Assuming the ripple counter to be reset, counting is enabled by the INSIDE signal. Counting may be disabled in one of two ways: The EMG leaves the amplitude window and the INSIDE signal disables counting (cases 1 and 2) or the count reaches octal 6000 (196 ms, case 3) and the STOP signal disables further counting. As soon as the minimum period is reached the PERIOD SENSOR flip flop is set and the PERIOD INDICATE OUTPUT goes high. This provides the comparision signal for the operator. In case 1, the PERIOD SENSOR flip flop is reset and that signal, together with the output of the analog to logical converter indicating that the EMG has left the voltage window, is sufficient to RESET the counter. In cases 2 and 3 the PERIOD SENSOR is set so the resetting occurs after the transfer has been completed. Transfer of data from the ripple counter to the accumulator of the PDP 8/S is initiated by the interrupt (INT) signal. This occurs when the PERIOD SENSOR has been set and the input signal leaves the window, thus data is not transferred for the case of "silent periods" under 8 ms. In addition to the logic circuit shown in Fig. 3, level converters were fabricated to interface the CMOS logic levels of the peripheral device to the DTL logic levels of the computer. PERFORMANCE
The repeatability and accuracy of any device are important performance parameters. Results were obtained both for one sample of EMG data, repeated 20 times through the device, to demonstrate source and device error combined, and for a constant known pulsewidth applied to the device, to demonstrate device error only. The results of the first test show that 95 percent of the measured silent periods were within ± 2.2 ms of the average length (See Table I). To eliminate the variability of analog tape speed, a second test was performed utilizing a constant pulsewidth from a signal generator. The results showed that the measured times are within ± 0.2 ms of the average at the 95 percent level of confidence, well within the design constraint (See Table II). The use of voltage thresholds for detection presupposes that the silent period is mainly a function of amplitude: this device also requires that the signal remain within this band for a minimal amount of time in order to be detected. With these assumptions, this device is somewhat limited as to the kind of signal variations it can detect. If a silent period occurs in the EMG with a rather slow decay of voltage level into the defined threshold levels, then it is very likely that the period will be
IEEE TRANSACTIONS ON BIOMEDICAL ENGINEERING, MARCH 1976
162
ANALOG TO LOGICAL CONVERTER
Fig. 3. Detailed logic circuit. This circuit provides a hardware realization of the silent period definition and implements the block diagram of Fig. 2. Not shown are level converters to interface the CMOS logic levels of this device to the DTL logic levels of the computer. A detailed explanation of the operation is provided in the text. The components used are as follows: D flip-flops: MC 14013; J-K flip-flops: MC 14027; counter: MC 14040; 6-input AND: MC 14501; 3-input NAND: MC 14023; 2-input NAND: MC 14011; inverters: MC 14009; and operational amplifiers: 741C.
.I!N.
EMG CASE 3
I/I-
-
CASE 1
CASE 2
INSIDE PD SENSOR BIT I BIT 0 (msb)1
1
I /'I,-
_
TABLE I DEVICE PERFORMANCE FOR TYPICAL EMG SIGNAL Minimum
Duration 81.856 ms
Maximum Duration 83.008 ms
Duration 82.531 ms
Standard Deviation 0.380 ms
20
2
46.656
51.072
47.603
1.181
20
3
67.840
69.056
68.592
0.314
20
4
73.664
74.752
74.429
0.354
20
5
73.215
74.816
74.432
0.497
20
Silent Period Number 1
Mean
N
STOPIIII READY INT
lop IOP 24
IOP4 RESET
TABLE II ''
,n
n
u VI
n
I
f
Fig. 4. Logic timing. Schematic rendering of the logic sequence for each of the three cases that implement the time window. Long times are shown dotted. For example, in case 2, the PD SENSOR goes high 8 milliseconds after INSIDE goes low, and returns low several microseconds after INSIDE goes high.
undetected or incorrectly measured. Experience with measuring silent periods from dozens of patients indicated that this occurs occasionally. Most other methods [151-[17] presently in use have time measurement errors much larger than the present device
because of limitations of the graphical recorders and the human error of determining when a silent period begins and ends. The method reported here minimizes the human measurement error and is constrained by device measurement error
Device Performance for Constant Pulse Width Input Input Pulse Width 30.600 ms
Minimum Duration 30.464 ms
Maximum Duration 30.720 ms
Duration 30.639 ms
40.000
39.872
40.192
40.056
Mean
Standard
N
Deviation 0.098 ms
50
0.103
50
only. The device error is also constant with respect to time and input signal variation. Additionally, this device has the capability of measuring silent periods in a real time environment, where previous methods are restricted to first recording the data graphically and then measuring the silent period. CLINICAL UTILIZATION Measurement Process: Operation of the device on typical data is shown in Fig. 5. The procedure used to measure the silent period duration is as follows. (1) Threshold voltages are determined from the EMG tracing for the channel selected and adjusted on the device. (2) All devices are started. (3) Calculations are initiated at the end of the sample by typing a
COMMUNICATIONS
163
RIGHT ANTERIOR TEMPORAL
LEFT
ASILENT
PERIOD
RIGHT MASSETER LEFT MASSETER
DIGASTRIC
JAW JERKS
F
5
0ml e 500 me
\
1
-
PERIOD SENSOR
Fig. 5. Typical data. The upper traces show the input EMG traces from five different masticatory muscles. The seventh trace gives the output of the peripheral used for verification of the existence of the silent period. The lowest trace is a timing marker. In this example the silent periods from the right masseter muscle are being measured.
character on the teletype keyboard. (4) The ordinal numbers of the desired silent periods are entered via the teletype. (5) The durations of the selected silent periods are printed at the teletype and optionally transferred to storage for later analysis.
CLINICAL RESULTS While the purpose of this communication is to describe the measuring device, some discussion of the use of silent period duration measurements is appropriate. DeBoever and Kovaleski [22] found that the number of silent periods decreased upon insertion of the occlusal bite plane splint (a recommended treatment in TMJ problems) but the duration of the remaining silent periods were not significantly changed. Beemsterboer et al. [14] examined the effect of the splint on the silent period duration after both the jaw-jerk and the openclose-clench cycle. The durations after treatment with the occlusal splint decreased significantly for the jaw-jerk technique. Surprisingly, they found further that immediately after the insertion of the splint the duration of the silent period fell to within the normal range. In these studies, however, numerous factors were uncontrolled and, as a result of the success of the above studies, McNamara et al. [15] undertook to examine some of these factors. Biting force, for example, was found to influence the duration: a decrease in duration was found with an increase in biting force. Another parameter, the angle at which the jawjerk taps are applied did not cause a statistically significant change in silent period duration. A third parameter, muscle length, also did not influence durations significantly. Software Support: The computer program associated with this device interactively controls the data acquisition and
processing by prompting the operator for documentation and receiving commands from the operator at the teletype.' After initiating measurements from the computer console, the following are carried out via the teletype control: A termination character ends the processing of silent periods. Documentation is requested as to patient, data, muscle, and other clinically relevant parameters for storage along with silent period durations. The ordinal numbers of the "true" silent periods are requested, and upon termination, the duration of each in milliseconds is printed. Optionally the documentation and durations may be stored on magnetic tape or punched on paper tape. CONCLUSIONS The advantages of the described device in processing electromyographic silent periods are manifold. The process with its on-line capability is faster than manual techniques, formatted hard copy is provided, human measurement error is eliminated, a consistent silent period definition is implemented, and the dental personnel are relieved of an ancillary task. The disadvantages are that the powerful pattern recognition powers of the human cannot be used to recognize out-of-definition silent periods or silent periods with a low signal-to-noise ratio. Thus a small fraction of the silent periods are still measured manually. Since the computer is used basically for pulse generator and data storage medium, this system could easily be extended to processing multiple channels simultaneously by constructing more peripherals with different device addresses. The basic
1Available on request from the authors.
IEEE TRANSACTIONS ON BIOMEDICAL ENGINEERING, MARCH 1976
164
device could also be altered to provide a self contained tool for portable clinical use. By altering the "analog-to-logical" converter, or the logical feedback from the counter, or both, many different voltagetime windows could be implemented and thus provide other applications for this device where event and timing applications are of interest. The investigations described above illustrate some of the uses of this device in the diagnosis and treatment of temporomandibular joint disturbances and indicate that the silent period has proved to be an interesting and useful diagnostic sign to enhance research intQ the controversial etiology and treatment of these disturbances. REFERENCES
[11 L. L. Schwartz, "A temporomandibular joint pain-dysfunction syndrome," J. Chron. Dis., vol. 3, pp. 284-293, 1956. [2] C. S. Greene and D. M. Laskin, "Splint therapy for the myofacial [3]
[4] [5]
[61 [7]
[8]
[9] [10] [11]
[12]
[13]
[14] [15]
[161 [17] [18] [19]
[20]
pain-dysfunction syndrome: a comparative study," J. Am. Dent. Assoc., vol. 84, pp. 624-628, 1962. C. Molin, "Studies in mandibular pain dysfunction syndrome," Swed. Dent. J., vol. 66 (suppl. 4), pp. 1-55, 1973. D. A. Kerr, "The pathology of traumatic temporomandibular arthritis produced by traumatic occlusion," J. Dent. Med., vol. 12, pp. 190-192, 1957. L. Schwartz and D. P. Tausig, "Temporomandibular joint paintreatment with intramuscular infiltration of tetracaine hydrochloride: A preliminary report," N. Y. Dent. J., vol. 20, pp. 219223, 1954. I. Yavelow, I. Forster, and M. Wininger, "Mandibular relearning," Oral Surgery, vol. 36, pp. 632-641, 1973. L. Schwartz, "Temporomandibular joint syndromes," J. Pros. Dent., vol. 7, pp. 489-499, 1957. S. P. Ramfjord and M. M. Ash, Occlusion. Philadelphia: Saunders, 1966, pp. 248-287. P. Goodman and C. S. Greene, "Response to placebo equilibration in MPD patients," Proc. Inter. Assoc. Dent. Res., vol. 52, p. 72 (abst.), 1973. J. A. DeBoever, "Functional disturbances of the temporomandibular joints," Oral Sciences Reviews, vol. 2, pp. 100-117, 1973. Agerberg and G. E. Carlsson, "Functional disorders of the masticatory system. I. Distribution of symptoms according to age and sex as judged from investigation by questionaire," Acta. Odont. Scand., vol. 30, pp. 597-613, 1972. W. D. McCall, Jr., P. F. Crane, D. C. McNamara, and M. M. Ash, Jr., "Phase plane analysis of jaw motion in functional TMJ disturbances," Proc. Inter. Assoc. Dent. Res., vol. 53, p. 173 (abst.), 1974. D. C. McNamara, P. F. Crane, W. D. McCall, Jr., and M. M. Ash, Jr., "Diagnostic implication of the occlusal velocity envelope of motion," Proc. Inter. Assoc. Dent. Res., vol. 53, p. 169 (abst.), 1974. P. Beemsterboer, D. C. McNamara, S. Holden, and M. M. Ash, Jr., "Effect of bite plane splint on EMG silent period duration," Proc. Inter. Assoc. Dent. Res., vol. 53, p. 169 (abst), 1974. D. C. McNamara, P. F. Crane, W. D. McCall, Jr., and M. M. Ash, Jr., "Myotatic reflex response to unloading and loading jaw-jerk stimulation," Proc. Inter. Assoc. Dent. Res., vol. 53, p. 205 (abst.), 1974. R. Bessette, B. Bishop, and N. Mohl, "Duration of masseteric silent period in patients with TMJ syndrome," J. AppL Physiol., vol. 30, pp. 864-869, 1971. H. S. Brenman, M. A. Black, and J. G. Coslet, "Interrelationship between the electromyographic silent period and dental occlusion," J. Dent. Res., vol. 47, p. 502, 1968. D. E. Beaudreau, W. F. Daugherty, and W. S. Masland, "Two types of motor pause in masticatory spindles," Am. J. Physiol., vol. 216, pp. 16-21, 1969. S. S. Altug, C. T. Childress, S. DeMund, and W. D. McCall, Jr., "An interactive computer peripheral to measure the electromyographic silent period," Proc. Inter. Assoc. Dent. Res., vol. 53, p. 202 (abst.), 1974. K. J. Hayes, "Wave analysis of tissue noise and muscle action potentials," J. AppL Physiol., vol. 15, pp. 749-750, 1960.
[21] E. Kwatny, D. H. Thomas, and H. G. Kwatny, "An application of signal processing techniques to the study of myoelectric signals," IEEE Trans. Biomed. Engr., vol. BME-17, pp. 303-312, 1970. [22] J. DeBoever and W. C. Kovaleski, III, "Occlusal splints: Effect on musculature of TMJ dysfunction patients, Proc. Inter. Assoc. Dent. Res., vol. 52, p. 169 (abst.), 1974.
Neural Control of Heart Rate: A Conciliation of Models PETER G. KATONA, MEMBER, IEEE, PAUL J. MARTIN, AND FELIX JIH Abstract-Two published models for the interaction of sympathetic and parasympathetic effects on heart rate are examined. The models appear to support contradictory conclusions: one was interpreted to imply no interaction, while the other one was said to indicate significant interaction between the two types of autonomic controls. It is shown that the two models are essentially equivalent, and that the different conclusions are due to different interpretations of the concept of interaction.
INTRODUCTION It is well known that the heart is under the dual control of the sympathetic and parasympathetic autonomic nervous systems. In an attempt to characterize the interaction between parasympathetic and sympathetic neural stimulation Rosenblueth and Simeone [1 ] developed a mathematical model to describe the steady-state effects of sympathetic. parasympathetic and combined sympathetic and parasympathetic electrical stimulation on heart rate. They concluded that the two types of stimuli exerted their effects independently of each other since the percentage change of heart rate caused by a particular frequency of sympathetic (or parasympathetic) stimulation was the same regardless of the background level of parasympathetic (or sympathetic) stimulation. More recently, Warner and Russell [21 presented another model for combined parasympathetic and sympathetic influences on heart rate, but they concluded that the sympathetic and parasympathetic influences interact rather than act
independently. Resolving the apparent discrepancy is desirable for at least two reasons. First, modeling is supposed to increase physiological understanding, and if two different conclusions are drawn from two different models describing the same system, a resolution of the discrepancy is a prerequisite for furthering a physiological understanding of the system in question. Second, recent reports indicate that cardiac disease may be associated with abnormal parasympathetic control, and that parasympathetic stimulation appears to have beneficial effects during acute myocardial ischemia [31, [4]. It thus appears that an assessment of the degree of parasympathetic cardiac control may be clinically desirable. Such an assessment must be based on an understanding of the interaction of sympa-
Manuscript received March 4, 1975; revised May 27, 1975, and June 24, 1975. This work was supported in part by the National Institutes
of Health under Grant GM-19599. The authors are with the Department of Biomedical Engineering, Case Western Reserve University, Cleveland, OH 44106.
