Electrical Impedence

Hello Wired Family!

I have my 3 month interrogation coming up and sadly, I still do not know what electrical impedance means on the report. My research coordinator has attempted to explain it to me, and I don't think I'm stupid or anything (LOL) I just can't understand the concept and what the electrical impedance part of the interrogation report is and means to me and the device? I know if anyone can shed some light on my brain some of the pros here can :)!

Thanks!!!!

9 Comments

Impedance OR Resistance

by donr - 2015-02-07 02:02:51

Mama: Does your device even give you an impedance? Didn't you get a new leadless MICRA device?

Anyway, here's what impedance is:

Every electrical circuit has three characteristics called Voltage, Current & Impedance. I'll have to explain them in mechanical terms because humans can sense those terms; they can only imagine (Visualize) the electrical equivalents.

Here goes. Go outside & put a garden hose on the faucet. Go to the end of the hose and turn it on - but first stick your thumb over the end of the hose. All of a sudden you will feel a force against your thumb, trying to push it off the hose end. The force is from the water pressure in the hose. The usual water pressure in residential buildings is about 45 pounds per square inch (PSI). You cannot hold that back very long (Unless you are Arnold Schwartzenegger) and the pressure forces your thumb off the end & you can SEE the water flow out of the hose end. BUT... you CAN restrict the amount of flow to make the water squirt farther - we do that all the time.

I have shown you how to FEEL PRESSURE, SEE FLOW and ADJUST RESISTANCE to FLOW.

Now keep those images in your mind & let's apply them to an electrical circuit:

1) The VOLTAGE is equivalent to water pressure. It is the electrical force that wants to push something through a conductor.

2) The water FLOW you SAW is the equivalent to electrical current through the conductor. In the case of an electrical current, it is extremely itty, bitty, teensy, weensy little gobs of electrical particles called "Electrons" No one has ever seen an electron - too small - so they draw them as looking like billiard balls with a little minus sign on their side.

So what is CURRENT FLOW in an electrical system? It's those little pool ball-like electrons flowing along through the conductor. Remember that they are so small we cannot SEE them & they do NOT come out the end of the conductor & make a puddle on the floor like the water does. There's one major difference between the water hose example & the electrical example. Water comes in lakes or can be stored in tanks. The pressure is provided by a pump & can flow out the end of the hose & make a puddle. Electrons cannot be stored in a bucket, they have to return from whence they came, so you have to provide a return path for them - called a closed circuit.

3) Now we get to RESISTANCE. In the water hose concept, the resistance to water flow was your thumb across the end of the hose that partially closed off the end. In the electrical system, it is the internal properties of the conductor that cause the electron flow to be less. Think of it as smaller & smaller spaces that the electrons have to squeeze through as they wander along the conductor. Sort of like your thumb across the end of the water hose.

Let's translate the things you can now visualize about things electrical into your PM leads. The FORCE that is going to make the electrons flow through the wire conductor comes from the BATTERY. One end of the conductor is connected to the NEGATIVE side, marked with a (- minus sign). The other end is connected to the POSITIVE side, marked with a (+ Plus sign). The electrons come roaring out of the - side & return to the battery at the + side. The quantity of electrons that flow through the conductor is called the CURRENT. The RESISTANCE to their flow cannot be DIRECTLY measured, it has to be calculated from the voltage & current values that CAN be measured directly.

BTW: The RESISTANCE to electron flow is also called IMPEDANCE; they mean the same thing & can be used interchangeably for your purposes.

Let's look at the IMPEDANCE in your PM system. The battery is connected through the little computer chip to one end of the lead.
1) The current flows down the lead (Which has its own resistance) to the tip of the lead that is embedded in the heart wall. The tip is surrounded by the scar tissue that formed around it while it healed.
2) That scar tissue has its own resistance to the current flow, also. Then the current travels through the heart tissue to make the muscles contract. Guess what?
3) The muscle has its own resistance, also. Then the current passes from the heart wall out into the blood inside the heart -
4) again, this interface has its own resistance.
5) It flows through the blood (Which, BTW is an excellent electrical conductor) having its own resistance & finally... 6) ...jumps back into the lead) (Another resistance).
7) It then flows back to the PM & into the battery to a grand welcoming party of all the other electrons.

The total resistance to the current in its journey to the heart & back is the SUM of all the resistances it met along the way. Go back & count - there are SEVEN of them - I conveniently numbered them for you.!!!!!

The PM has a little man with a meter sealed up inside it. Every night, he awakens to run out & determine the IMPEDANCE of the leads & stores it in the computer's memory.

Since the battery has a finite, FIXED voltage, as the LEAD IMPEDANCE increases, the amount of current the BATTERY can force through the lead & heart decreases as the IMPEDANCE increases. (Remember the hose - the pressure stays constant. As you (or Arnold) squeezes harder, the flow of water decreases).

There is an OPTIMUM (Fancy word meaning "BEST") current through the heart muscle that is known to the PM to give the OPTIMUM contraction of the muscle. Your PM uses the measured IMPEDANCE every night to determine whether or not the heart is getting enough electrical energy to properly contract. If it knows the IMPEDANCE, it can calculate how much voltage is required to force that optimum current through the heart & adjusts the voltage across the two ends of the lead. It does this by creating some voltage spikes from the battery using transistors. These spikes can be higher than the battery voltage.

There, in a nutshell (A VERY LARGE Coconut).

Hope it all made sense to you.

Donr (Resident Geek)

Keep me updated

by tammyjk1021 - 2015-02-07 03:02:28

Let me know how that 3 month visit goes. I'm not looking forward t that little wand on my first visit I can tell you that. The first time she checked it, it nearly scared me to death.

GOT IT DON!

by Runningmama - 2015-02-07 05:02:31

DonR, I can always count on you my fellow El Chami buddy! I'll tell him you got the concept across to me, he has tried and failed more than once. LOL You made it crystal clear to me and the last paragraph was just what I needed. And yes, my MICRA does have impedance so to speak. It has everything a normal pacemaker has just sealed up inside. The little tines that attach it to my ventricular wall act as leads just like yours that run to your battery do. They grow into the tissue just like yours do, but mine serve a dual purpose. They are not only the leads, they also hold the device in place until my heart tissue finally just encapsulates the device completely, which at 3 months, has probably happened. I know after 3 months it cannot be removed (without open heart surgery, but we don't think about that EVER because barring the sky falling, that would NEVER need to happen, and the sky does not fall, although it would make for a fun evening LOL ). First time my impedance was 490, then six something, last time I was up to 640 and 700 is perfect. Let's see what I'm at when I pay the piper this week!

Tammy: I look forward to the readings, look at it this way, we are getting checked, they are looking at us and the device to check and make sure we are all set. I do hate it when the programmer makes my heart beat fast, that still freaks me out, but hey, I do it so often I've just started making myself have random conversation with everyone in the room and I talk right through it or make jokes about it....It's over soon. This concept helps relieve my anxiety quite a bit. Remember, you are in a major medical center, one of the best in the world, and are having an awesome piece of technology checked out by highly trained professionals, if something is wrong, you are in the right place at the right time and with every check up, you can rest a bit more assured that your new gadget is working. With trust comes acceptance you will be there soon!

I hate having to have the chest xray part of the study so often and don't forget our 3 month questionnaires...yep, time to do that again too. Did you find that your first one was open ended like mine was? none of the questions applied to the situation at hand for me or so i thought. "are you anxious? well, i'm in cardiac pre op and you are asking me questions, so yep. " "does your heart condition affect your daily life? Well I'm getting a pacemaker, so you tell me"...LOL You'd think they'd have better research questions, wouldn't you?

I will send you a note as soon as I get home with my results, etc...IT WILL BE ALL GOOD! and let me know if I can help you.

I'm going to ask this week if our PM's are safe for the optometrists equipment, like the optomap, etc considering the electric fields, or does anyone know?

I wonder if.....

by donr - 2015-02-07 08:02:15

....any others share an EP or cardio? We could be the only pair.

OK, so now I know you get a check. I hadn't wondered about it, but how do the make contact w/ it? They hang a "Hockey Puck" right over my PM & the two talk to one another via magnetic fields. How do they get to yours?

Also, verrrrrry interesting that it will be totally encapsulated in such a short period. Now I understand more about that little buddy.

BTW:" How about more info abut how your PM is going. All the details about what they do & how they do it. This is new countrry you are exploring & I think the Geeks & nosey hosts would like to know more about this project.

What you are experiencing is a quantum leap in technology - far more advancing that any other experienced since the first implantable device was installed. All the rest have been evolution - this one, IMNSHO, is revolutionary. In some ways, yours is like jumping off a 3 meter high diving board - once you take the step, there is no way whatsoever to go back. You are as committed to what you are doing as a hog is to a breakfast of ham & eggs.

Mama, what you are experiencing in those questionnaires is as stupid as the first question I was asked while lying on the ER bed after being T-Boned by a Jeep Cherokee doing 35 MPH. "Hi, How you doing?"

You should read the answers I give to such stupid questions.

Unless the optometrist uses something I haven't seen, it's a "Not to worry event." It's done w/ lasers & they do not require magnets to function.

I have a similar test on Monday for macular degeneration. been done on me at least half a dozen times w/o any effect at all.

Donr

Here's How It Works...

by Runningmama - 2015-02-07 08:02:46

The pacemaker programmer from Medtronic talks to my Micra the same way they would talk to yours. I call it a little doughnut like thing that gets put over my heart and they communicate with it using a programmer (it's contained a briefcase looking otter box thing kinda like the nuclear football the Potus carries or something) LOL. El Chami is real excited about it for sure. He watched my treadmill test after it was installed (they like to see how it works under exercise stress) and then he loved how it looked on the Chest CT I got 2 months ago, to check it more. Every 6 months after the first 3 months I get a chest xray to make sure it hasn't moved or anything. Which it has more than likely grown into the tissue by now, so I'm all clear on that front.

As far as how it works, it's a standard single chamber pacemaker that acts just like any other standard single chamber pacemaker, sort of. It stays in stand by mode until it senses my heart beat go below fifty or that my heart does not beat for 1.1 seconds so I'm told. When either of those things happens, I get paced. My paces are generated from inside the "capsule" and delivered via the tines attached to and grow into my heart (they are kinda like fish hooks). The entire pacemaker is about the size of a vitamin (shorter than a nickel and as slim as a .22 caliber bullet) in fact on a chest xray it looks just like a short .22 bullet in there...

As far as it never coming out, it's so small, there is room for plenty more micras (or pacing leads if I need a regular pacemaker down the road). When it's time to replace, this Micra gets turned off and a new one gets put in right beside it. The fact that it never comes out kinda bothered me a bit at first, but then I realized that pacing leads never come out either nor do heart stents. Something had to live in my heart forever, might as well be a Micra TPS. And, If I can help someone by being part of the project then good; let's face it, I'm good research. Someone my age and fitness level with no other health issues (except some asthma) can give the gadget a run for its money. If it can keep up with me at my level, then it can keep up with someone much older or at a different level of activity, too. AND IT DOES...it's like the little gadget that could.

Did I mention that it also broadcasts WIFI so the pacemaker nurses at Emory can check its status and working ability all the time? I can call the arrhythmia clinic and Frank can see what's going on. Medtronic even talks to it through WIFI randomly to see how it's doing or what it's doing or how it's adjusting itself. Every night, it takes "inventory" of how much battery, voltage, etc it has used during the past 24 hours and adjusts itself accordingly so as to be as energy efficient as possible. There is rate response capability as well, but mine is turned off. Does this all make sense?

My physical recovery only took a few weeks, and that was not from the pacemaker, it was my leg where the catheter was put in (the nurse said they used the biggest sheath she had ever seen). In three weeks I was on my treadmill again, within 6 weeks I was lifting weights again, now all normal. I had horrible anxiety you know the stuff we talked about, but now I'm just like everyone else. Except I have a nano battery living in my heart.

I hope all this helps, you know how I ramble on and on and on..LOL. Good Luck on your test Monday, let me know how it goes !!!!!!

It's an Elephant I Eat One Day at a Time

by Runningmama - 2015-02-07 09:02:39

WillieG, this whole experience is like an elephant that I'm eating one bite at a time, sometimes it's good sometimes it's bad...the anxiety really gets to me sometimes actually alot of times.

I knew from the beginning research or not, that I would not be able to get used to the leads, etc. so I got the Micra and I'm glad I did...

Oh, and secret is out..DonR and I have the same EP. Like he said, I bet we are the only pair in the club.

Micra

by WillieG - 2015-02-07 09:02:56

Really enjoyed reading about your experience with the Micra and glad all is going well for you. I had wondered how they would ever remove it. So I guess your heart has room for many since you are young!!! I think I would prefer of PM as this big chuck of metal is hard for me to accept!

Thanks, too, Donr for your nice explanation on impedence. You give nice explanations!

impedance

by Tracey_E - 2015-02-07 11:02:14

I can't explain it either! But, when my lead went bad I know the impedance went up. And when it starts to go up, that's how they predict how much longer the battery has. I think it normally stays the same. Where's Don?? He can explain it!

Check this out. Skip to page 34
http://pacericd.com/documents/IBHRExAM/Fundamentals%20Of%20Cardiac%20Devices.pdf

Good description of Micra....

by donr - 2015-02-08 12:02:18

.....implant, Mama!

Glad it is going well for you. I've gotta say it - from the tone of your last comment, you have once again proven Napoleon's Maxim "In battle, the mental is to the physical as three is to one."

How many others in here have a Micra? Any Idea?

I was surprised at the EXTREMELY small size of it by your description. I'd like to know what materials the semiconductors are based on to be that small & do so much.

Donr

You know you're wired when...

Titanium is your favorite metal.

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