BME 552 exam 1 2009 SOLUTION

BME 552 exam 1 2009 SOLUTION - BME552 Exam1 March6,2009 1.

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BME 552 Exam 1 March 6, 2009 1. The specific values for the three electrode model for this questions are: R s = 10,000 Ohm, C = 0.1 uF , R p = 10 MOhm. a. Two plots are shown below. One shows voltage in response to a current pulse (100 uA for 0.1 ms). One shows current in response to a voltage pulse (6V for 0.1 ms). Identify which plot came from constant voltage stimulation and which came from constant current stimulation b. The pulses start at t=0+, calculate the V(0+) for the constant current pulse and the I(0+) for the constant voltage pulse. c. Based on the shape of the current waveform in each case, explain which type of pulse might be more effective for stimulating nerves (amount of neural activation for a given amount of charge applied). d. Which type of pulse will best use the charge injection capacity of the electrode (assume platinum metal) SOLUTION a. Plot A is voltage response to constant current, plot B is current response to constant voltage. b. V(0+) = 100 uA * Rs =1 V (C is a short circuit, so no current through Rp I(0+) = V/Rs = 6V/10 KOhm = 600 uA (C is a short circuit so potential drop is all across Rs). c. Nerves respond more efficient (with less charge) when the charge is applied in a short period of time. The voltage pulse has a current spike at the beginning, so more charge is being applied at the beginning of the stimulus. d. I gave credit on this problem for a variety of answers as long as the reasoning was good. The current pulse has lower current amplitude, initially, so the charge can more readily dissipated by Faradaic
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BME 552 exam 1 2009 SOLUTION - BME552 Exam1 March6,2009 1.

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