EE 305 Project_1 The Effective External Defibrillators

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EE 305 Project_1 The Effective External Defibrillators

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EE 305 Project_1 The Effective External Defibrillators

  1. 1. The Effective External Defibrillators Project - #1 Kehali B. Haileselassie&Faisal alsaadi 08/14/2013 ELC ENG 305 – Circuit Analysis II Instructor - EbrahimForati
  2. 2. Table of Contents Introduction…………………..…….……………………………………………………….. 3 Design Procedure….…………….…………………………………………………………... 4 Simulations……….…………….………………………………………………………….... 8 Results………….…………….……………………………………………………………… 9 Analysis………..……………………………………………………………………………. 11 Conclusion…………………………………………………………………………………... 13 References…………………………………………………………………………………… 14
  3. 3. Introduction: A basic defibrillator is a device that can send a current from an external source through the heart to restore the electric current within the heart. The shape of the current is vital to make a heartbeat properly. It is this waveform that mimics the motion of the heart and enables it to deliver good blood flow. There have been two defibrillation waveforms that have had the most success in passing an electric pulse to a heart, allowing it to receive the signal and restore normal heartbeats. The two waveforms used in defibrillation are the Lown waveform and the Biphasic Truncated Exponential Waveform (BTEW). The Lown waveform is made of basic electronic components in series. An electric charge is stored in a capacitor and then passed through an inductor and the output across a load, namely an arrested heart. This design was the standard for defibrillation devices until the mid-1980s. It was at this time that a biphasic waveform was thought to be more effective. The Biphasic Truncated Exponential Waveform (BTEW)defibrillator was believed to be an improvement over the monophasic waveform developed.Some advantages are portability, battery life, and cost (Witt). However, the biggest advantage may be that biphasic defibrillator has a greater success rate of working on the first pulse compared to the monophasic defibrillator because of its fundamental signal. Many advances in defibrillator have been made in the healthcare field. With the application and improvement of electric waveforms, the defibrillator has also made many advances, such as manual internal defibrillation devices and automatic external devices.
  4. 4. Understanding the construction of the waveform is vital to success in ventricular fibrillation. The focus of this study will be output and application of the Lown and biphasic waveforms. Using a limited selection of basic electrical components, the two types of waveforms must be created while keeping cost to a minimum. Resistor, capacitors and inductors will be the only components allowed along with a direct current power source. Procedure The signals of for the defibrillator have been shown in figures 1 and 2. Signal 1 is a monophasic signal using an underdamped Lown waveform and signal 2 is a Biphasic Truncated Exponential Waveform (BTEW). The desired output for the signal takes the form of Vo = K1*e-ζω0 t sin[ωt]. Knowing the following relationships: ω0=1/√(LC) and ζω0 = R/2L Fig. 1 – Original Lown waveform from design specificaitons
  5. 5. Fig. 2 – Original Biphasic Truncated Exponential Waveform from design specifications ω0 can be found from the figure 3 and ζ can be calculated thereafter. The design procedure for creating a circuit capable of mimicking the desired output is a best done through selecting the necessary components from the list of available parts. Inductor Values for determining ω0 [from ω0 = 1/√(LC)] L = 100 mH L = 220 mH Capacitor Value ω0 Capacitor Value ω0 0.047 µF 14,586 rad/s 0.047 µF 9,834 rad/s 0.1 µF 10,000 rad/s 0.1 µF 6,742 rad/s 1.0 µF 3,162 rad/s 1.0 µF 2,132 rad/s Fig. 3 - ω0calculation from available parts The choice of inductors was most limiting. The available inductors were either 100 mH or 220 mH while the choice of capacitor was one of six ranging from 22 nF to 100 µF. Through simple evaluation of the choices presented, the value of ω0 = 9,834 radians works best when trying to get close to a frequency: ω = 2П/T = ω0√(1-ζ2 ) = 1000П rad/s
  6. 6. for T = 2ms. The damping coefficient ζ calculated from ζω0 = R/2L = 4,545.45 rad/s is 0.46222. From these values, an RLC series circuit configured as depicted in figure 4 is optimal for the Lown waveform. When determining the output for a BTEW, it is advisable to build a first order circuit, which can reduce cost significantly. A capacitor in series with a resistor will give the desired output. An RC first-order circuit has the time constant of τ = R*C. Evaluating the original signal, the half period is observed to be 0.4 ms. The half period is used in the biphasic circuit because the polarity is reversed halfway through the total period. By creating a circuit that has a τ similar to the half period, a signal will emerge that resembles the wanted output. Using a 0.1µF and a resistor of 2.2 kΩ the time constant is0.22 ms which approximately equals the half period of 0.2 ms. The optimal design for the BTEW is depicted in figure 4. Fig. 3 – Lown monophasic circuit configuration
  7. 7. Fig. 4 – Biphasic Truncated Exponential Waveform circuit.
  8. 8. Simulations Using LTSpice as a circuit analyzer, figures 5 and 6 portray the intended output for the derived solutions. Fig. 5 – Simulated Lown waveform output Fig. 6 – Simulated BTEW output
  9. 9. Results The results of the output signals are depicted in figures 7 and 8. Figures 9 and 10 show the results of the values for voltage and time for the original, simulated, and experimental signals. Fig. 7 – Experimental output of Lown monophasic waveform
  10. 10. Fig. 8 - Experimental output of BTEW Original Peak 1 (V) Simulated Peak 1 (V) Experimental Peak 1 (V) % Error Original Peak 4 (V) Simulated Peak 4 (V) Experimental Peak 4 (V) % Error 13.2 12.3 12.78 3.18 -3.23 -2.30 -2.34 27.55 Original Peak 2(V) Simulated Peak 2 (V) Experimental Peak 2 (V) % Error Original Peak 5(V) Simulated Peak 5 (V) Experimental Peak 5 (V) % Error 9.4 9.7 10.2 -8.5 0.6 0.31 0.275 54.2 Fig. 9 – Lown waveform signal comparison of max and min voltages
  11. 11. Original Peak 1 (t) Simulated Peak 1 (t) Experimental Peak 1 (t) % Error Original Peak 4 (t) Simulated Peak 4 (t) Experimental Peak 4 (t) % Error 0.25ms 0.255ms 0.266ms 6.4 1.263ms 1.26ms 1.25 ms 1.02 Original Peak 2(t) Simulated Peak 2 (t) Experimental Peak 2 (t) %Error Original Peak 5(t) Simulated Peak 5 (t) Experimental Peak 5 (t) % Error 0.6ms 0.653ms 0.62 ms 3.33 1.646ms 1.62ms 1.63 ms 0.9 Fig. 10 – Lown waveform comparison of time differences Analysis When analyzing the circuit for price, the least expensive circuit will have the least components. Because of the extremely high voltage necessary to resuscitate a heart, component voltage, amperage, and power ratings must also be very high. After, the most significant factor in creating the circuit is the margin of error between the original design specifications and the physical circuit. When comparing the Lown waveform, he first half of the signal has an average margin of error of 3.6%. The second half of the generated signal does not reach the minimum voltage of the design specification. Instead of reaching a minimum of 0.6 V at 5T/6, we were only able to reach 0.275 V. This left a much higher margin of error for this part of the circuit at nearly 25%. However, the timing of the circuit was nearly exact with an average margin of error of 1.94%. The BTEW circuit fared even better than the Lown waveform with an average margin of error of 9% and a timing margin of error of 0%. The final designs are within an acceptable range compared to the original design when taking cost and size into account.
  12. 12. The significant design flaw in either circuit is the lack of backup components in the case of failure. If any single component fails, there is no way to salvage a dependable waveform. This flaw is unavoidable and may make the product undesirable.
  13. 13. Conclusion When the two types of circuits are compared against each other, it appears that the BTEW clearly outperforms the Lown waveform Some advantages of the biphasic defibrillator are that it is more portable because of its smaller size. The biphasic waveform can be constructed more easily and with less parts making it less expensive. The power source necessary for a biphasic defibrillator is usually a battery and can last longer. Perhaps the biggest advantage of the BTEW is the ability deliver two beats for every period, increasing the chance of successful resuscitation on the first pulse (Witt). The biphasic truncated exponential waveform is closest to the original signal, cheaper to construct, more effective in application, smaller, and has greater battery life. The recommendation is that the BTEW defibrillator be used. References
  14. 14. 1. Gliner et al. Circulation 1995;92:1634-45 2. Lown, Bernard. "Biography of Dr. Lown: Co-founder of IPPNW."BernardLown.org, n.d. Web.29 Mar. 2013. <http://bernardlown.org/bio.html>. 3. Tang et al. Journal of American College of Cardiology 1999;34:815-822. 4. Witt, Pharaba. "The Advantages of Biphasic Defibrillators."EHow. Demand Media, 20 Oct. 2010. Web.

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