# Defibrillator and electric field lines

1. Oct 12, 2008

### Kathi201

I am asked to draw a picture of a person 1 second before patient is defibrillated and 10 seconds after a patient is defibrillated. I am asked to draw a general picutre of the electric field lines and charges at these two points. I know that the goal of defibrillation is to enterfere with the reentry of circuits to bring the electric activity to a stop of to eliminate fibrillation. Does this mean that the amount of electric field lines after defibrillation is less than the amount of electrical activity before?

This question is somewhat confusing for me so any help or explanation would be appreciated!

2. Oct 12, 2008

### marcusl

Can you display the question exactly as it is written? Your post seems to be missing some information.

3. Oct 12, 2008

### Kathi201

Sure...here is the question

A defibrillator is used to shock a heart back into action. Below, a picture of a person is shown with the approximate placement of defibrillator metal electrodes before shocking the patient. Draw a cross sectional view of the body (very simple sketch) and show the electric field lines and charges 1sec before the patient is defibrillated. Sketch the same cross section again and show the electric field lines and charges 10sec after (long time after) the patient has been defibrillated. Also describe your pictures in words.

I can not draw a person on here so I am just trying to figure out generally what the picture should look like but the problem is really confusing me.

4. Oct 12, 2008

### marcusl

Well, I also think this is poorly worded problem. Her's my best shot at a helpful hint.

Before and after defibrillation, charges in the heart are the only electric sources present. During fibrillation, the heart lacks coherence so the source distribution is chaotic and multifaceted--there will be numerous positive and negative regions. You can draw the fields from these regions and show that they fall off rapidly with distance so there is very little to measure at the electrodes.

During normal heart activation, there is an orderly progression of activation (through, say, the ventricles). REsting muscle has a negative potential, activated muscle positive, and so you can draw the field lines as emanating from across the boundary. In fact, a useful approximation is to treat the heart sources at an instant in time as an equivalent electric dipole. You can draw dipolar fields in the body, in other words, as a reasonable approximation.