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Unformatted text preview: Due Friday, Jan 24, 2011 BME 201, Spring 2011 - HOMEWORK #1 RC Circuit and Strength-Duration Relationship Problem I. In the strength-duration relationship, “strength” of the stimulus that is required for exci- tation can be expressed as current magnitude, final value of the transmembrane potential, total charge, or total energy delivered by the stimulus. The last quantity is especially im- portant in the implantable devices: if the task (e.g., excitation) can be performed with the minimum energy possible, the battery of the device will last longer, which means longer periods between surgeries for the patient. In this problem we will investigate a strength-duration relationship expressed in terms of total energy. Consider an RC circuit analog of the passive membrane, stimulated with a rectangular pulse: C R I v (t) m s m m Figure 1: RC circuit model of a uniformly polarized membrane patch. For the rectangular pulse of duration d , the total energy delivered by this pulse can be computed as E ( d ) = I 2 s ( d ) R m d, (1) i.e., as a square of the stimulating current multiplied by the surface resistance of the mem-i....
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This note was uploaded on 09/03/2011 for the course BME 233 taught by Professor Izatt during the Spring '11 term at Duke.
- Spring '11