Lecture Slides Week 8 Slides

7/27/2019 Lecture Slides Week 8 Slides

1/59

Bioelectricity Week 8


2/59

Bioelectricity -- Week 8

Bioelectricity Week 8:

Stimulation

A) Galvanis observationsB) Spherical cellC) Cylindrical fiber, with timeD) Field stimulation

Train system: -- Control


3/59

Bioelectricity Week 8_2

Stimulation Train system: Control!

1. Introduction to week 8

2. What is meant by stimulation?3. Why analyze stimulation?

4. Analyze Passive instead of Active?5. Single Spherical Cell.6. Strength-Duration Curves

7. Stimulation of a cylinder with cuff electrodes

8. Stimulation , the Tiger function9. Field stimulation, the field10. Field stimulation, the consequences

11. Week 8 in review

12. Good-bye and Special Thanks


4/59

Stimulation

by Galvani


5/59

Galvani experiment, more modern view


6/59

In bioelectricity, stimulation means

The use of electrical currents to influence the action of

excitable tissue.

Often it is used to initiate action potentials.

On other occasions it is used to stop action potentials.

And it can be used to modify function, as done by Galvani.


7/59

Duke University Gardens


8/59


9/59


10/59



11/59





4. Why Analyze Passive instead of Active?5. Single Spherical Cell.6. Strength-Duration Curves

7. Stimulation of a cylinder, Tiger function

8. Stimulation with cuff electrodes9. Field stimulation, the field10. Field stimulation, the consequences


12. Special Thanks


12/59


13/59

LinearityIn the context of stimulation

Linearity means that the voltage changes produced by twosimultaneous stimuli are equal to the added results of each oneseparately.

In stimulation linearity cuts the analytical work in half, or more.

Thats because stimulation usually involves 2 or more electrodes, for example, source

and sink. Often linearity means that results from only one electrode have to be found.

The other can be handled with parameter changes, and then added.


14/59

So we will analyze..

..several geometrical arrangements of stimulus electrode and

tissue.

The geometries are sphere, cylindrical cuff, and cylindrical field.

These are chosen to demonstrate different principles of

stimulation.

Each geometry gives insights useful in the others, and in realstimulation as well.


15/59


16/59









12. Special Thanks


17/59


18/59


19/59


20/59


21/59









12. Special Thanks


22/59

Strength-duration

Io

Weiss-Lapicque equation

Re-arrange and divide by R.

T is the time required to reach the threshold vm .


23/59

Strength-duration graph

Weiss-Lapicque equation

Ith is the current strength required to reachthreshold vm in stimulus duration T.


24/59



25/59




2. What is meant by stimulation?

3. Why analyze stimulation?4. Analyze Passive instead of Active?5. Single Spherical Cell.6. Strength-Duration Curves

7. Stimulation of a cylinder, cuff electrodes

8. Stimulation, Tiger function9. Field stimulation, the field10. Field stimulation, the consequences


12. Special Thanks


26/59

Stimulation of a cylindrical fiber

using a cuff electrode drawing of currentpattern


27/59


28/59

Steady state vm what is the significance of

the minus sign?


29/59



30/59





4. Analyze Passive instead of Active?5. Single Spherical Cell6. Strength-Duration Curves

7. Stimulation with cuff electrodes

8. Stimulation, the Tiger function9. Field stimulation, the field10. Field stimulation, the consequences


12. Special Thanks


31/59


using cuff electrodes steady state vm, no time in the equation here.(This is what we showed before.)

So how long does it take to get to the time when this equation is right?


32/59


using cuff electrodes vm as function of time aswell as distance.

Your instructor calls thisequation the Tiger function.Other people do not use thisname.

Tiger function:


33/59


34/59

Graphs of vm with time in it


35/59



36/59


37/59

Field stimulation, the ideathat is, where current is going, as a picture


38/59

Field stimulation, the beginning1st imagine the activating function established by the electrode


39/59

Note proportionality between vm change with

time and activating function

Rate of change with time,

at the start of excitation,for a fiber at rest.

Activating function (named by Rattay)


40/59



41/59









12. Special Thanks


42/59

Field stimulation, where it goes, convolution

The response depends on the activation function convolved with the Tigerfunction

Here f() is the activating function,and G() is the Tiger function.


43/59

Field stimulation, where it goes, drawing

Here f() is the activating function, and G() is theTiger function.


44/59

Stimulation

by Galvani

Creating an activation function andconvolving it with the Tiger function


45/59



46/59







8. Stimulation with cuff electrodes9. Field stimulation, the field10.Field stimulation, the consequences


12. Special Thanks.


47/59

Week 8 in Review - 1

We know now that the stimulation creates action potentials, and the actionpotentials propagate, release calcium ions, and the muscle contracts


48/59

Week 8 in Review -2

With a spherical cell model one knows that strength and duration interact toreach a vm level sufficient to initiate action potentials.


49/59


50/59


51/59


52/59

Reviewing the course


53/59

The train


54/59


55/59









12. Special Thanks


56/59

Bioelectricity extends Special Thanks

To you, in this first offering of the online course.

Thank you for your patience, perseverance, andgood humor throughout the weeks of study of a

complex subject.


57/59

Roger Coke Barr extends Special Thanks

To you, as a student in the first offering of this online

course.

Thank you for your patience, perseverance, and

good humor throughout the 8 weeks of study of thisfascinating but complex subject.


58/59

Roger Coke Barr also extends Special Thanks

To Robert Plonsey, Emeritus Professor of Biomedical Engineering at Duke.Professor Plonsey is the senior author of the Bioelectricity AQA text on which this

course is based. His precise presentation of fundamental principles in

mathematical form has served to provide a foundation to the whole field of study.

To Madison S. Spach, Emeritus Professor of Pediatrics and Physiology at Duke.Professor Spachs leadership of research in cardiac electrophysiology and originalinsights in electrophysiological theory and experiment have energized all the

faculty and students around him.

To Andrew E. Pollard, Professor of Biomedical Engineering at the University ofAlabama at Birmingham, whose boundless good humor, original thinking, and

systematic development serve as a continuous stimulation to keep thinking and

keep having fun.


59/59

Sarah Duke Garden, Duke University

Documents

Lecture Slides Week 8 Slides