Portable Stimulator Design Aimed at Differentiating Facial Nerves From Normal Tissues

Transcription

1 Journal of Medical Systems, Vol. 28, No. 2, April 2004 ( C 2004) Portable Stimulator Design Aimed at Differentiating Facial Nerves From Normal Tissues S. Kara, 1,2 S. Kemaloğlu, 1 F. Şener, 1 M. Okandan, 1 and M. A. Erkan 1 Facial nerves are very prone to risk of being cut away in the facial surgeries. In order to differentiate the normal tissues from the nerves during the surgeries, facial stimulator is very essential. These stimulators are particularly useful in triggering action potentials in the facial muscle tissue. In the case of any damage to these nerves, paralysis is unavoidable. Second use of the stimulator would be to diagnose how severe the facial problems are. Third use, which is a noninvasive application, is the employment of facial stimulator to treat and diagnose facial problems that arose from temperature differences, cuts or strain. The stimulation is achieved through DC voltage pulses that conform to user-specified amplitude, pulse duration and pulse intervals. These variables are set according to the age, sex, and physiological conditions of the patient. Peripheral Interface Controller is used to derive different pulse patterns. The current specifications of our stimulator are a range of V pulse amplitude, msec pulse duration, and sec pulse interval. The main benefits of our stimulator are its graphic display that shows the form of pulse, its compact size, and operation on a battery power supply and adaptability to convert to other stimulation applications. KEY WORDS: facial nerve; stimulator; facial surgery; portable stimulator. INTRODUCTION Motor afferent and sensory nerves make up the facial nerve system. Motor ends of the facial nerves trigger the mimic muscles leading to facial movements. In the case of any damage to any part of the facial nerves, one or more than one of these movements might be lost and partial paralysis might be unavoidable. (1) Any neurological disorder, cut and strain of the nerves in the facial surgeries can cause this type of damage. (2) Since, especially facial movements and mimics mean a lot 1 Deptartment of Electronic Engineering Biomedical Engineering Group, Erciyes University, 38039, Kayseri, Turkey. 2 To whom correspondence should be addressed; kara@erciyes.edu.tr /04/ /0 C 2004 Plenum Publishing Corporation

2 178 Kara, Kemaloğlu, Şener, Okandan, and Erkan Fig. 1. Block diagram of facial nerve stimulator. during the social interactions with people, any disorder of these mimics depress the patient psychologically. Facial nerve stimulators are particularly useful in the study of bioelectric phenomena, where they can be used to trigger action potentials in the facial nerves or muscle tissue in a very controlled and reproducible manner. Especially in the facial surgeries, the nerves are very prone to risk of being cut away. Therefore facial stimulator is very essential in differentiating the normal tissues from the nerves during the surgeries. (3) Second use of the stimulator would be to diagnose how severe the facial problems are. Third use, which is a noninvasive application, is the employment of facial stimulator to treat and diagnose facial problems that arose from temperature differences, cuts, or strain. (4) Fig. 2. Top-view of the facial nerve stimulator and surface electrodes used.

3 Stimulator Design Aimed at Differentiating Facial Nerves From Normal Tissues 179 Fig. 3. Flow diagram of software. PD = Pulse Duration; PI = Pulse Interval; PA = Pulse Amplitude; SD = Stimulation Duration.

4 180 Kara, Kemaloğlu, Şener, Okandan, and Erkan MATERIALS AND METHODS The stimulation is achieved through DC current pulses that conform to userspecified amplitude, pulse duration, and pulse intervals. These variables are set according to the age, sex, and physiological conditions of the patient. The stimulus is monophased and in the form of a square wave. The specifications of our stimulator are a range of V pulse amplitude, ms pulse duration, and s pulse interval. Surface or needle electrodes transmit the electrical pulses from the stimulator to the nerve. Conventional electrocardiogram electrodes are most commonly used. Needle electrodes are helpful in obese patients. The block diagram of the whole system is depicted in Fig. 1. Fig. 4. Analysis of the stimulator output signals on the oscilloscope screen.

5 Stimulator Design Aimed at Differentiating Facial Nerves From Normal Tissues 181 The pulse duration, pulse interval time or frequency, and application time of the stimulation is adjustable through the setting buttons present on a compact enclosure equipped with a liquid crystal display (Fig. 2). These parameters are processed and recorded at PIC 16F877 microcontroller enclosed and the end-view of the stimulation can be visualized on an LCD. (5,6) The pulse amplitude of the stimulation signal formed with the PIC is amplified and sent to the electrode pair through an isolator circuit. The applied stimulation can be fed back to an amplifier circuit that is connected to a loud speaker. This is achieved via electrodes navigating on the face. A buzzing voice from the loudspeaker would be heard when stimulation is delivered to the face. (7) The flow diagram of the program coded in the microcontroller can be seen in Fig. 3. RESULTS AND DISCUSSIONS The designed portable stimulator is first set for an amplitude level of 5 V, pulse duration of 2 ms, and pulse interval of 50 ms and the output waveform is visualized and checked on a digital oscilloscope. The set parameters are then changed to a pulse duration of 1 ms and pulse interval of 100 ms while amplitude is kept same. In both cases the set parameters complied with their analysis on the oscilloscope screen (Fig. 4(a) and (b)). The sensitivity of the pulse duration is found to be 1 µs. The circuitry of the system is all-digital, which offers the advantages of having lower impact from environmental temperature, humidity, and pressure changes with compared to the analog circuitries. We had to pay close attention to the correct application of electrodes because even slight displacements could result in considerable changes in stimulation current requirements. In addition, electrodes were placed cautiously so the device stimulates the nerve not the muscle. CONCLUSION The main benefits of our design are its graphic display that shows the form of pulse, its compact size, and operation on a battery power supply and adaptability to convert to other stimulation applications. Since low batteries can cause stimulator problems, we need add a charge level indicator to warn for battery replacement. One other useful application of our stimulator could be for diagnostic purposes, where response of the facial nerves to the applied stimulation is investigated to determine any facial disorder. REFERENCES 1. Yazgan, E., and Korürek, M., Tıp Elektroniğii, Istanbul Technical University Publications, İstanbul, Yiğitbaşı, G., Priferik Fasiyal Paralizililerinde Elektrodiyagnostik Testlerin Yeri, Erciyes Universitesi Tıpta Uzmanlık Tezi, Kayseri, 1993.

6 182 Kara, Kemaloğlu, Şener, Okandan, and Erkan 3. Fisekovic, N., and Popovic, D. B., New Controller For Functional Electrical Stimulation Systems, Medical Engineering and Physics, Vol. 23, pp , Kara, S., et al., Yerel Anestezi İçin Elektronik İyon Geçiş Hızlandırıcısı, Biyomut 98. İstanbul, pp , PIC 16C/16F Microcontroller Databook, Gray, P. R., and Meyer, R. G., Analysis and Design of Analog Integrated C., Wiley, New York, 1994.