Computer generated transcript

Warning!
The following transcript was generated automatically from the content and has not been checked or corrected manually.

Hi, this is Maggie Marsh Nation. I want to introduce Brett Netherton who is doing another wonderful presentation on basic eeg electrical concepts and safety. Go ahead and take your first slide. This, uh, this topic, I've talked on a lot before and I've been doing, do, doing these talks for quite a few years and they always evolve and I've added new stuff to this. So this is your basic circuit. You've got your patient, you've got electrodes, of course, you've got a bunch more electrodes in this. But for simplicity's sake, you've got your head Boxx, you've got a cable from your head Boxx to your EEG machine. And then you've got a power cord that goes from there too, the outlet. And I think that's a good place to start when we consider, um, not only electrical safety but electrical concepts as well. Um, there are, uh, uh, there are a few things that we're gonna do. We're gonna cover some basic electrical principles that are just good general things to understand before we jump on to physiologic principles and before we jump on to safety issues that we face, so I'm just gonna jump right in to the basic electrical principles this, you all recognize it's that handy dandy wall plug and it's got three holes in it. And, uh, um, you, uh, probably are, are well aware of those. But what are they? Well, um, we know that one is ground, one is neutral and one is the hotline. What does that mean? Um, let's start at where electricity comes from. Whether you're talking about a huge, um, electrical generator at the bottom of a dam or a nuclear station or a small hand held generator. Like the army guys might use the same basic physics. Electromagnetic principles apply when you move a magnet. I'm sorry, when you move a wire, like the one shown here through a static Matic field, such as the one shown if you have a closed loop, a current will be generated in that wire. And guess what? That is the basis upon which all of our electricity is generated. Now, let's take a closer look at just that Sinusoid, it's the power signal, right? That's what comes out of the wall. We know that it rotates around something, let's just call that neutral. And we know that it goes up and down and up and down, right? And we know that it's 100 and 20 volts or actually 100 and 18 volts. Well, that's the hot voltage and instead of 118 volts that, that's actually the root mean squared, the DC equivalent. Did you know that it's actually 340 volts peak to peak. So it goes up and down 340 volts. Now, we talked about this wall plug the neutral, the hot, the ground. Let's put those into perspective. We know that the hot voltage is the ones going up and down. We know that the neutral is the zero line, let's say around which it alternates. The ground is actually a wire, a heavy gauge, big wire in the wall that goes where it goes to the ground. That's why they called it ground. And in most of your facilities, it will actually connect into water pipes and where do the water pipes go? They go into the earth. So it actually connects into ground. Ok. So in summary, we know that this wall plug here has ground neutral and hotline. Notice that the neutral is a larger slot than a hotline. Why? Well, we want to make the hotline very hard to get into. Now, why should you never let your child run a screwdriver into the neutral line? Well, perhaps the electrician got the two wired backward. Would it still work? Yes, but for safety's sake, we like the, the neutral to be zero volts. The hotline is the um 120 volts. And then of course, the ground, you know where that goes to the water pipe. Ok. This is a little concept that I use to explain Elms law. It's very simple but I found that it works. All right, you're gonna have to put your imagination to work. And you got three folks. Ok. Um uh One is standing in a big container full of wet concrete. One is standing in a big container full of jello and one is in a container with nothing. So they're standing in air now, air passes a quarter to concrete at the same time, the concrete passes a quarter to Jello. At the same time, the Jello passes a quarter to air. So just imagine this, these folks are standing in these containers full of jello or wet concrete and air and they're having to move their arms through the wet concrete or through the Jello or through the air to pass these quarters. OK. That is not unlike electrons flowing in an electrical circuit in the, in the uh quarter circuit, we have a current flow of quarters in the electrical circuit, we have a current flow of electrons. Now, let's think about effort. We have air concrete and Jell O who do you think is putting the least effort in to pass the quarters back and forth air, right? The person that's in air. It's real easy to move our arms back and forth. Who's putting in the medium effort? I would be the person that's standing in. Jello. Jello is fairly, I don't know, fairly uh uh easy to move your arms through compared to wet concrete who has the most effort. It's the wet concrete. Now, if we bring that concept over to our electrical circuit, where do you think the least voltage buildup is? Now, it takes that w when the current flows in this circuit, a voltage will build up on those impedances. Where do you expect the least voltage build up the small impedance, the medium impedance or the high impedance, it's the small impedance. Where, where do you expect the medium voltage build up? Well, it's on the medium impedance. Where do you expect the most voltage build up? It's on the high impedance. There is another way to say this, that it takes a high voltage to push current through a large impedance. It takes a medium voltage to push current through a medium impedance. It takes a small voltage to push current through a small impedance. So we're gonna bring these concepts into future discussions. Now we're gonna move on to parallel pathways. OK. Why am I looking at these race cars driving around this circuit? Well, if there's only one pathway for those cars to go, um they're gonna stay on that pathway. If we have two pathways, two parallel pathways, look, look to me like half the cars are going in one pathway ha half the cars are going on the other pathway. The same as it is when you drive to work. If you've got a way you're gonna take that shortcut, right? And the same as with circuits, the path of least resistance. And if there's more than one pathway, the current will s will split depending upon which is the easiest. Why are we talking about this? Well, doesn't this look familiar? We have your patient, we have electrodes, we have the amplifier box and we've got a current flow, don't we? So the generator here is where the generator is your patient's brain, right? That's where the voltage comes from, that drives a very tiny current through your electrodes to the amplifier. Can you imagine where some potential parallel pathways might be here? S one you should be able to see now the the red line that's rotating around simulating a current where along the scalp, why would we have that? Maybe we have a sweaty head, maybe you have gel gooped on the patient's scalp. What did we do? We created a short circuit, didn't we between our electrodes? If the short, if it becomes too much of a short circuit, we will actually stop recording in our electrodes. Why? Because we completely sorted out the scalp? Is this a parallel pathway? Sure. Is that a desirable parallel pathway? No, this is an example that most eeg G folks can relate to. There are other parallel pathways when it comes to safety. Let's take a look at one. An example of coupling with a power cord, we move it near our wires, we get lots of coupling. How about a medical grade power core? Well, we get a lot of coupling with it when we move it near our wires. Also, we just showed this power cord coupling, we know that if we put this power cord near our lead wires that um we will pick up that signal. What about if we have that power cord near our amplifier? Will it pick up the signal? Sure. What about if we have that power cord near our near our power cord? Will it pick up the signal? It can? What about if we have the power cord near another power cord? Can we pick up that signal? Yes. Are all of those unwanted parallel pathways where we pick up signals? Yes. So that is why parallel pathways are important. So those were some basic electrical principles. Let's bring those and we're going to talk about basic physiologic principles. Then we'll bring those two together in safety issues we face. So basic physiologic principles. These are relative electrical numbers in our world. You're gonna, you're gonna understand a lot of these, the sensory evoked potential typically around 10 microts eeg around 20 microts. EKG or ECG around 1.5 millivolts, evoked potential motor, maybe 2.5 millivolts, em MG, perhaps three millivolts. And we've already discussed that the wall voltage is 338 volts. If you're like me, it's hard to visualize numbers without some examples. So if we assume that one micro volt is equivalent to one inch, then the tiniest signal. The sensory evoked potential of 10 microts is equivalent to a sheet of paper, 8.5 by 11 sheet of paper eeg is equivalent to a, to a large stool ecg is equivalent to a tall tree. A motor evoked potential is equivalent to a 17 story building emg would be like a 21 story building and wall voltage, the 338 volts would be equivalent to the distance between Miami and Anchorage. That's pretty significant. So when we consider our physiologic signals, a sensory evoked potential, it's like trying to find a piece of paper somewhere between Miami and Anchorage, Alaska. I'll give you a helicopter in a couple of hours. Go find that paper. It's not easy to do so, relatively. The voltages that we face in our lab are huge compared to the physiologic voltages of the body. Now, we have a resistance system system to protect us from dangerous stuff from dangerous voltage from dangerous currents. What are the relative resistances of the body? We have high resistances, tendon fat bone are very resistant. We're very, very resistive over 100,000 s. What about medium well, skin depending upon the where it's at and who the skin is on is medium from 40,000 S to 100,000 ohms. You take a carpenter who works outside, very tough calloused hands. Their skin is probably upwards of 100,000 ohms impedance. A baby is gonna have low impedance, skin. Same with geriatric populations. What about lo well, nerves, blood mucous membranes, muscle is very low resistance, very low impedance and it can be less than 1000 ohs. It's basically goop. Think about it, nerves, blood mucous membranes muscle. It is very wet, very, it, it has a lot of salt in it. It's very conductive. So when we remember our discussion on concrete Jell O air, where do you think the concrete is the high, the high resistances? The jello would be the medium resistances and the air would be the low resistances. Now, look at the drawing over here. We have some critical systems, the cardiovascular system, the respiratory system, the lungs, the brain, the spinal cord, the renal system, the kidneys are all very critical from an electrical safety standpoint. And I want you to notice where are they? They're in our brain in our gut. Ok. Now we're gonna bring this to current and probable effects if we're talking one milli ap one milli ap we might have on our skin might give a tingling sensation, almost not perceptible 3 to 5 milli aps. Oh man, you let that go. An average child is gonna feel it. They're gonna let it go 6 to 8 milli aps uh for an average woman a little bit higher. For an average man, they feel it, they let it go. They got shocked. Then we move to the maximum current a person can grasp and let go. You grab 16 mli aps and you're really gonna get a shot. The next step is tetany of skeletal muscles. You grab that you can't let go because your muscles are in tetany because it is firing and causing them to not be able to let go. Then the next step is paralysis of respiratory muscles, respiratory arrest. In other words, I I can't talk because your respiratory system would be in shock 20 to 50 milli aps, 100 to 500 or 50 to 100 milli aps is the threshold for basically your heart stopping through the onset of ventricular fibrillation. Here's something very important. OK. And well, two amps is, is asystole, the heart's just gonna stop beating. Look at these values 50 to 100 mili aps. Now let's look at common household circuit breakers, 15 to 30 amps. Maximal intensity of household current 240 amps is 50 amps. A lot larger than 100 milli aps. It's huge in comparison. So again, the current that the body can handle safely without damaging these critical systems that we've already pointed to are very small in comparison to the common household circuit breakers. Is that a dangerous situation? Well, it sure can be. Now remember these are considering constant voltage, the wall voltage is constant voltage, it's on all the time. Now, I know that I'm talking to Ee Gers, but I bet that some of the folks out there have also used stimulation for evoked potentials. We use pulse stimulation, not part. In other words, it's part time voltage, just tiny pulses. We do not use constant voltage like we're talking about here. But that wall outlet is constant voltage. Let's talk about how people get hurt or die from electricity. There are acute impact and look more latent impacts acutely. The cardiovascular system, the respiratory system, the brain and cord and the kidneys all have acute damage, cardiovascular various arrhythmias, asystole, it can stop feeding, respiratory arrest back where I can't talk. The lungs just can't work. Um brain and cord. It's if uh there there's many instances in the literature of the spinal cord actually being split in two when a uh bolt of lightning hits it um or just shut down renal system, a not your failure. Now, on the latent side, in other words, after an immediate response, cardiovascular respiratory brain and cord and renal, I want you to notice tissue necrosis, tissue necrosis, tissue necrosis, tissue necrosis. Most of the injury from electricity happens in a in a latent fashion through tissue dying, critical tissue such as cardiovascular respiratory brain and cord or or kidneys. And once that tissue dies, the system, cardiovascular respiratory brain cord renal has enough of a negative downside on the body once it's dead, that the that the body itself might die. Now, when we, when we look at the body as a whole, how is it that we protect the body. We already know it's from the concrete or the, the jello, the skin. There are pathways that we don't want current to flow. The current, the the injury has three primary factors, current intensity, current pathway and duration of exposure. How long it's on there? In our situation, we can really only control one of those if we're talking about dangerous currents. It's the current pathway. Where do we have something on the patient that could allow a current to flow in the body? Where don't we want current to flow? I'm gonna show you two pathways. Here is one from the right arm to the left arm and vice versa. So if it's from one arm to the other, where does that dangerous current flow? Remember our critical systems, the heart, the lungs, the brain, the kidneys that's in our gut, right? So if that current is flowing from arm to arm, we have to, it has to flow through the gut, right through those critical systems. Here's another pathway from a leg up through an arm or the or the brain again, going through the critical, the critical area where the critical systems are the heart, lungs, brain and kidneys. So think about it when in the event that you do evoke potentials, where do we have stimulating electrodes? Well, they might be on the wrists or they might be on the ankles and you have electrodes on your patient's head all the time. OK. Let's move on. We're gonna talk about a very important factor. We put electrodes on the patient, right? Sweat decreases the body's defense against electrical injury. How often um do our patients get sweaty? Our patients get sweaty all the time and uh let's move on micro shock and micro shock, micros shock is a term used in cardiology to note to denote a low level electric current applied directly to myocardial tissue. The heart as little as 0.1 milli aps causes ventricular fibrillation. Remember that first slide, we it's a it's a tiny amount that can actually cause ventricular fibrillation. Um macros shock is uh is when we have a moderate to high level of electro current passing across two areas of intact skin. Approximately 100 milli aps can cause ventricular fibrillation. What's the difference? Macros shock? It was on the inside. Remember concrete Jell O air. What was air? It was the goop, the, the nerves, the blood, um the muscle, it one if the shock occurs on the inside past the skin, only 0.1 mili aps can cause cardiac death, ventricular fibrillation, 0.1 milli aps. However, if it's on intact skin, how much 100 mili aps is 100 mili aps larger than 0.1 milli aps. Absolutely. It's 1000 times larger. So we want to keep the skin intact skin. We wanna make sure that intact skin is in place. Now, remember this, remember how, what sweat does what do TECT do to intact skin along with this sweat? We already know our patients are sweaty. What do TECT do to intact skin? We un intact it, don't we? So what do you do every time you rub your patient's scalp to get a better impedance, you're un intact skin. I'm not saying that's a bad thing. We have to get good impedances. All I'm doing is pointing out that we in what we do slightly decrease this natural protective nature of skin, don't we? And now when we move into the safety issues, we face just remember you already have electrodes that are attached to skin where you have decreased the impedance as much as possible, correct? So what are the safety issues that we face? Well, I pick five that uh they could be covered in a timely fashion and they're very important. Number one wall, voltage, direct electrical shock and ground loops. Ok. What about direct electrical shock? Um Obviously, if we connect our patient to uh to the voltage in the wall, that's, that's bad. Right. Well, uh the old two millimeter pins were mandated to be removed to be no longer be used by the FDA. I think it was in 2001, but I think it's still important in the event that you ever see any of these old two millimeter pins you should know. Don't use them. Notice the old two millimeter pins. What would happen if you stuck that into an outlet, you could get, your patient could get shot right with this new, the D 42 82 standard that I'm certain you guys all use. Is there any exposed metal? No, there is not. So if you stuck this into a wall outlet, which you're certainly never going to do, it would be protected. Ideally from that voltage. This is not such a big deal. We never use these old two millimeter pins, but you'd be surprised how often they were used before and actually stuck into a wall outlet. The second item was ground loops. I hear this. I hear this question very uh uh frequently about what are these ground loops and why are they important? I'm gonna go through an explanation to ex explain as best I can ground loops. And I, and we start with birds sitting on the uh on the wires up on the um uh uh you see it all the time, the birds fly up there and they sit on the power line, power lines. Why can birds sit on power lines? Um It is because they're not grounded. Just think about it. You look at the birds sitting up there on the wire, they're only touching one side, they're not, they're not touching both sides. The circuit is no, in this drawing, one is sitting on the neutral and one is sitting on the hot. So what if a big bird say big bird from Sesame? Street big flies up there and touches both of them. Well, he gets shocked and probably gets, gets fried. So, would the same thing work for humans? Well, sure it would. You could jump up there if you were the bionic man, you could jump up there and grab a hold of, of the line and you would not get shocked because you were only touching one side. Now, I wanna ask a question. Is it easier to touch a grounded piece of metal in the clinical setting or to touch the hot voltage line? I want you to look around where you're at right now. I would imagine that everyone on this call, I'm looking, Dena Denise, Diana, Angela Margaret Nancy. Sorry for anybody else. I've missed. Look around you right now. Look at the wall voltage, look at metal in your, in your clinical setting. Look at your computer, there's probably metal on there. Look at maybe the floor, maybe there's pieces of metal. Look at your walls, look at the doorways. Chances are if you go touch those pieces of metal, you re actually touching the ground. It is very easy to touch ground. Most stuff is grounded. Your computer is probably grounded. Your eeg machine is grounded when you touch your EEEEG machine chassis, when you touch the metal on the outside of your eeg machine, your fingers are physically from an electrical standpoint. It's the same as going outside and putting your fingers down in the dirt. So we use, use a ground electrode, right? Why in the world would we use a ground electrode on the patient? If it means they can get shocked easier by the hotline? Remember the birds up on the wire, how could the bird get shocked if it could if it was big enough to touch both of the both lines to complete the circuit? So I ask again, why in the world would we ground a patient if it means they can get shock easier by the hot voltage? Very simple leakage current, we're gonna come back to this. But now let's move on to ground loops. Why do we or do we use earth ground anymore on our patients? Do we use that? No, we don't, we do not use earth ground on our patients. We do not use that ground that connects to the water pipe. Why not? Because of the danger from crown loops? That's why the powers that be stopped using the earth ground. What the heck are the ground loops? Here are two pieces of equipment. Let's turn them on. And you can see all of the electronics are working inside of that equipment. Let's create some fault inside of the equipment. So that current is flowing to the outside of the equipment so that if you touch it, you're gonna get shocked. Look at the piece of equipment that is not grounded, it s flashing red where that current is accessing outside the machine. Look at this machine that is grounded. Where is this current that's getting to the chassis going? It's going down here through this wire up through this wire and out through the ground hole through the water pipe into the ground. Let's bring in some patience. This patient is grounded using an earth ground. What's going to happen? He gets, he gets shocked. The leakage current will flow from the chassis of the machine through his arm down through his leg, through that ground to where to the earth, it's the current wants to go home. The current wants to go to earth. What about the grounded piece of equipment? Here is a patient that is grounded, birth ground. He's happy. The leakage current from the chassis is not going through him. There's a path of lesser resistance through the ground and to the outlet ground. But that doesn't explain what ground loops are here. They are. This is the classic definition of a ground loop, let's say you have your EEG machine and it happens to have an earth ground and it's connected to your patient and somewhere else in your lab. There's another piece of equipment for something else that's grounded and that's attached on another location to your patient. Now, there is a lab, ground wire in the wall of your lab, right? Remember, look around you. Now, each one of those outlets in the wall has a huge ground wire and it's attached to all of the other outlets in your lab. And that wire goes to where it goes to a water pipe somewhere in the basement of your building and then it goes to, goes to the ground outside. So here you can see that big wire in the wall. Ok. And even though it's a big wire, does it have some resistance? Yes, it does. Now assume that the lab down the, down the hallway has some refrigerator in it. It's malfunctioning and it's got a lot of leakage current going through the ground. Remember our concrete Jell O Air. When you push a current through some impedance, what happens? You get some voltage buildup, right? So you've got a voltage build up on that resistor. What does this voltage do? Any voltage wants to drive a current? It drives a current through the circuit. Do you see a circuit? Well, yes, there is one. It's right here. It comes down through this line through this ground, down through the wire, down through the wire to the leg of your patient, up through the torso of your patient, through those critical areas to the shoulder where the other ground is attached from the other piece of grounded equipment up through the wire through the wire through the wire, ultimately to that ground and back through the circuit. This is the classic definition of a ground loop. Now, with your equipment grounds, do you have to worry about that? No, you don't let's take a look. Here is your EEG machine, your handy dandy, brand new updated eeg machine that you have in your lab. There is your patient. There's your amplifiers, here's a bunch of electrodes you've got attached to the patient. You, there is your amplifier box ground. OK? And you, you put it here, you put it on somewhere on the head, you put it somewhere on your patient. Here is your EEG machine ground, right. On modern eeg machines are your amplifiers and electrodes electrically isolated from your eeg machine. Yes, they absolutely are. They're usually optically isolated, electrically isolated means that they're not connected electrically. So your amplifiers, your amplifiers inside of here are electrically isolated from your EEG machine. On modern ee systems is the amplifier box ground. This green wire here. Is it the same as the eeg machine ground? It's absolutely not with isolated grounds such as the ones that we use. Can you use more than one ground? Yes, you can with isolated grounds. Can you have ground loops not from that isolated ground? You cannot, maybe there's other equipment that's connected to the patient that could provi provide a ground loop but not from your machine. Now, here is a very critical part for the test that you take when it comes time to register for EEG for IM for long term monitoring for nerve conduction studies. There might be a question on that test that says, should you use more than one ground. What should you say? You should say? No, I shouldn't use more than one ground. Be caught. Why? Because those questions are from back when equipment used earth ground. Do we use earth ground? No, we do not. So remember for the test, be sure to say no, I'm only gonna use one ground but on modern day equipment you can use more than one ground. Um The next, the next danger that I wanna highlight is electromagnetic energy. It's not so much for you in the EEG lab. But let's we're gonna show it anyway. We already showed this. We already saw through the video. If you put a power cord near your recording wires and activate it, there is a capacitive coupling field that comes up here and what happens in your lead wires, you actually pick up that signal and we saw that in the video and that was through capacitive coupling. OK? But I want to show um a video of that actually through another um source of electromagnetic energy. Here's a quick demonstration of capacitive coupling using a simple transmitter from a cell phone around 300 to 500 hz loose pair lead wire monitored here when we activate the transmitter on the cell phone. When it fires, you can see it's picked up in our wires that is picked up through capacitive coupling from the transmitter through the air to the wires. In this example, the power cord, we saw that we could pick up the signal in our lead wires. We also saw in the cell phone example to pick up that energy in our lead wires. And for the most part, that's really not gonna be dangerous, is it, it just causes us artifact in your lab. In the eeg lab, there are probably not pieces of equipment that give out enough energy this way to actually create dangerous currents in your lead wires. But is that possible? It absolutely is. And we're about to see an example. But in the operating room, there are many sources of primarily the electrosurgical unit. The Bovi it gives off uh 10,000 volts and it can be plenty burn your patient through your electrode sites. I did want to point though as far as the electromagnetic energy as being um a a potential danger, maybe even in your lab, maybe you have something that is emitting a huge amount of energy. Certainly, this next example of radio frequency energy from MRI is tremendously dangerous. And it's a similar concept. OK. Here's the MRI machine. We have our patient that goes in the MRI machine and they come out what happens. There's complex magnets and radiofrequency energy sources inside. OK. And inside of the bore there is a RF or radiofrequency pulse coil, it bathes the bore of the MRI with a pulse of radiofrequency energy at a very high frequency of 63 mega HTZ, 63 million times per second. That thing fires and it helps with the image. Well, um it can come in different configurations such as the full body coil shown here or here is a bird cage configuration just for imaging around the head. Now impedance due to capacitive coupling decreases dramatically with the increasing frequency. In other words, a capacitor doesn't let direct current flow, but it does have an increase or a lower impedance when the frequency goes up 63 million HZ is a very high frequency. Remember we had capacitive coupling from the power cord, which is at what? 60 HZ? And we picked up that in our lead wires. Do you think that we might pick up some of that signal from our, from the MRI and our lead wires when that signal is 63 million Herz compared to 60 HTZ? Absolutely. And it is very dangerous to this R energy. Our electrode lead wires look like antennas as a result. Significant electrode burns can result. And the RF pulse coil is the overwhelming source of electrode burns from Mr. Um So here's an example, this three year old, you can see these lesions right here. I think they were full thickness le uh I forget. Uh yeah, full thickness circular burns noted at the points where these were EKG electrodes, these were not necessarily small diameter. Um They're just surface electrodes, gelled electrode pads and you can see these locations. So um the point is that MRI uh is is uh that radio frequency energy from MRI can be quite dangerous. Now, AC and DC leakage current is uh is one of the primary ways that you will have a potential injury source for your patients in the lab. Remember up here, we talked about ground loops and how we do not have ground loops from our isolated grounds anymore. But since we, we do not have earth ground anymore, DC and AC leakage current can be dangerous for our patients. Let's take a look. Here's our amplifier box, here's the cable from our amplifier box too. This is an old neon coding machine that I've got. Here's our wall voltage comes in. What if the machine is on? And we have one of the wires, the insulation on one of these little wires here gets a little frayed and it comes in contact with something near the power side of the wall voltage and it jumps to this piece of metal which goes to this capacitor or lead wire, which goes to this piece of metal over here which ties in somewhere else. And it follows this big piece of metal to this big piece of metal, follows that piece of metal over here and it gets onto our amplifier. Is that a possibility? I guess it could happen. But remember our amplifier, our amplifiers are isolated from our patient connection, right. So this actually being a dangerous current that gets to our patient through our lead wires is probably a very, very, almost inf intestinal small chance of occurring. However, this next one, which is where that current goes out here and just sits on the metal chassis of our equipment is probably much more of a real chance of da of danger. How many times have you throughout your life? Have you touched a piece of something? Maybe a toaster and you get shocked or a refrigerator and you get shocked or your, your machine, your, your equipment in the lab and you, you actually feel a shock. That was because there was some leakage current probably coming from the power in it. Where did it go? It wound up sitting on some point of the chassis where you could touch it and get shocked. This is, this is one of the largest sources of, of danger in our labs. And the way to avoid it is to have frequent biomed checks from your bile meed department. When they come in, one of the things they actually do is they check all around the chassis for leakage current. We want to avoid extension cords. You've heard that before? Why? Ok. Here is, here is an EEG machine with the regular power cord connected to uh uh to an outlet. Here is another EEEG machine connected through an extension cord to the outlet. Now, let's assume that we've got an ex, we put it near AAA another table and this one is near another power cord. Ok? We know that we have current flowing. We already saw that. Remember in our example of the power cord coupling? Well, do you think that we get the coupling here? Yes. Did we get twice as much here and here as we got here? Yes. So we have twice the leakage current into our cable here as we do on this one. Absolutely. Which would you prefer? Obviously you'd prefer this one. And finally, DC electrochemical burns. This is another very important thing that you need to be aware of. What the heck am I talking about? DC electrochemical burns? When DC current is applied to skin, two things occur acidic buildup under the A node, the positive basic alkaline build up under the cathode. The negative. Each is capable of creating a bad burn, a bad electrochemical burn in a short time. Now, I know you're not satisfied with that. You'd probably like to understand a little bit more about it. Let's talk about it. Here is tissue. Here are our electrodes. Let's take a closer look. There is a piece of metal. In this case, a subdermal needle, I tissue tissue is goop. It's got all these ions in the, in the middle of the electrode. You've got electrons in electrodes. Electrons are the charge particle that moves to make current flow in tissue ions or electrolytes are the charged particle that moves to make current flow. Let's take a close look here. We have two electrodes attached to your patient, they're full of electrons. This e with the minus sign are a bunch of electrons just waiting the flow. Now, in our tissue, the goop, we've got sodium chloride, potassium chloride h2o we've got a lot of different chemicals that are in ion forms sodium ions, chloride ions, hydrogen ions, hydroxyl ions. They're all distributed out through tissue. Nothing is happening. There's no current flowing. Let's put a battery. Now, a battery is direct current, right? So it has a positive and a negative, positive negative positive negative. We have a positive electrode, the A node, a negative electrode, the cathode, we have a positive electrode here. Do you think that some of these negative ions throughout the tissue might want to migrate towards that positive electrode? Likewise, do you think that some of the positive ions in the tissue might want to flow towards that negative electrode? Yes. And that's exactly what happens. The longer this flows, the longer this current flows this direct current, the more negative ions migrate towards the A node and the more positive ions migrate towards the cathode. Do you think that that is a dangerous situation to have all of these negative ions sitting here? Do you think it's dangerous to have all of these positive ions sitting here? Do you think that it's possible that we could get some chemical reactions from all of those being in one location? Yes. And that's exactly what happens we have bubbling out of oxygen gas fairly harmless. We have bubbling out of hydrogen gas fairly harmless but we also have at the A node. Hydrochloric acid. Anybody think of a place where hydrochloric acid is also at? How about her stomach? It is a very robust, dangerous acid and it will build up at the A node at the cathode. We have an even more dangerous situation with sodium hydroxide. Does anybody recognize that? How about lie? It is a very dangerous basic chemical and these lesions they build up uh will be more the longer the duration of this direct current, the longer duration you'll get more and more acid and alkali build up and the more current, the higher the intensity of the current, the more acid and alkali build up, you will build up. Now, this a acidic reaction at the A node is self-limiting which means that it will, it will wind up, you could say burning itself out through various chemical reactions. Unfortunately, this this alkali reaction with the sodium hydroxide will keep going until it is removed until it is wiped away, until the tissue is gone, it will go straight down to the bone. So particularly under the under the cathode, this is a very dangerous situation and one that should be paid attention to, especially given this next instance, this is something that was published in uh the journal of Clinical monitoring and computing. A patient wore a plasm gra um on her left thumb to look at the blood flow to her left thumb and uh uh EKG ground on her right leg. During surgery, she complained of pricking pain on her thumb before the surgery. The anesthesiologist said, oh, everything's ok and went ahead and put her to sleep after the surgery, she had lesions on her left thumb and right leg. The lesions were dark gray, dry necrotic lesions with small perforation near the center. Uh under the uh EKG electrode, there were multiple discrete puc ta lesions. Um This could have been avoided. Um If your patients ever complained to you of pain from the electrodes, stinging under the electrodes. Should you listen? Yes. Um It might be from some leakage current in your machine that is somehow making it through that electrode to making through the lead wire through the chassis somehow to your electrodes. This is probably not gonna occur with your EEG equipment. However, if you ever have anything that's battery operated that actually has electrodes that attach to the patient, which let's face it, you probably don't, but especially if it is battery operated and you do happen to have that you should be very aware of this. The key point is in our conclusions, avoid using extension cords, get to know your biomed engineering staff. Um This is critical. This is I think a lot of people and I see this a lot. They uh uh I'm not sure what these biomed engineering guys do they come, they check out the equipment. But hopefully, now you understand that it's critical that they are looking for leakage current that could be damaging. You should know the dangers of the Bovi. I did not cover that since this was talking about the uh um beg and not the or you should keep your biomedical equipment checks up to date, learn your equipment. Uh Whether or not you have isolated amplifiers and ground chances are you do, but you should certainly know for sure. And finally uh embrace electrical concepts. They're fun and good for your career. This is the MRI radiofrequency pulse coil. It operates at 63 million hz 63 million times per second. It fluctuates, it pulses the Bovi, the electrosurgical unit pulses around 300,000 times per second. It can have discharges of 10,000 volts. It is used to basically burn tissue at the wand that the surgeon uses. And I if any of you guys go into or you will see that, that Bobi, it actually is this horrendous thing that they use to cut tissue with and cauterize tissue with burn tissue so that it stops bleeding. Um Our electrodes can be our electrode lead wires, in particular through capacity coupling can be a pathway to capture some of that energy and return it to our electrodes. And if you happen to use subdermal needles which have a very tiny surface area of around 15 square millimeters, you can actually get a burn in that electrode. The same way that the surgeons want is burning tissue. And if the surgeon discharges it in the air accidentally or on purpose, it's like a radio signal. And what is the best pathway back to the patient's body? In many instances? It's our electrode lead wires which act as in tennis anyway, that's a summary. Ok. Anyone have questions? Um I have a question. We um travel to our patients in the rooms and sometimes uh we have to unplug the beds and then the bed is not grounded, but the patient may have a monitor on with a separate ground and we're putting our ground on. And I recently read a medical paper that said electric, that if there was a power surge that, that, that power is going to surge from the point of one ground to the other on the patient, that would be, that would be dangerous for you if the ground that you used on your equipment was an earth ground. However, it is not an earth ground. It is an isolated ground. So II, I would, I would check that. How old is your equipment? Our equipment is not that old. Um Then it has an isolated ground. I'm certain of it. It, what, what's the manufacture of the equipment are you there? Yes, it's ok. Ok. Um, then I have, I have would, I'm 99% certain that your equipment is new enough that it uses isolated grounds. And in that instance, no matter whether there is a power surge that did flow through the other equipment's ground to the patient, it is your ground is isolated. You, you know what your ground is like, your ground is just like another one of your amplifier or 11 of your lead wires, it's completely isolated. So you, you, I would not worry about that situation since you use isolated grounds. OK. Thank you. You know, bra I heard you say one time that in describing what isolated um ground is, is that the signal is carried electrically up to a point and then it becomes like a, a light signal like someone using Morse code with a flashlight to get it from one side to the other so that current can't flow through that. And I thought that was a wonderful description. Yeah. The other thing I mention is about coiling up uh lead wires and taping them down, which is something I did for years. And, and when I heard your lecture, I went uh oh, because I was creating something that was um was bad and especially in the or, and, and since then I've been encouraging people to tape down a zigzag and as a stress reliever rather than make a loop because I think a lot of people are still making loops, stress loops for sleeping pe GS if you're monitoring uh arms and leg movement or some something like that you put a stress loop in so it doesn't get pulled off, but it's not actually as good a practice as taping down a zigzag. I'm going to, um, show a movie. Um, and, and I'll just talk through it. Here's one loop of wire and it's rotating through that magnetic field, creating a current, every loop of wire. What did we do to current? Generate it? We doubled it. So, if you are, if you're putting loops of wire and, and you've got your electrodes and you're, you're creating a bunch of loops and you're taping them down every time you loop it. What did you do for potential um current pick up from dangerous electromagnetic fields? You doubled it or you, you added, if you, if you did three, you tripled it. If you did four, you quadrupled it, et cetera. So I don't know if that makes sense that that is one of the reasons why it's dangerous for us to loop our lead wires. And is that the same thing as like if you bundle them all together, like, you know, you just take them all together and put them straight or no, only for cap for capacitive coupling. Yes. Um For um inductive coupling to a small extent. Yes. For, from a safety standpoint, you're far safer to have the lead wire stretched out straight. What if they're all straight and then you, and then you tape them together, then that's the absolute best thing you could ever do. I, I have a question. Um There's uh in one hospital that I work at there we use caps. OK. And some of the caps are really loose and I was able to go ahead and tape down, you know, in between the electrodes. Does that have an effect on the electrode? No, it doesn't. No, no. OK. Now, tape is a um tape is non conductive. So, uh it, it, it should do nothing to the electromagnetic field. Uh-huh. OK. Um I do want uh let me show you guys this one thing. Here is a loose para lead wire. Here's a ribbon, para lead wire, here's a twisted para lead wire. Can you guys see this? Yeah. OK. Um Here is when, when we move, this is a little different. When you move a magnet through a loop of wire, you can generate a current in that wire. And we already saw that when you have a radio frequency source of noise, you can generate a current in the wire, right? So if we put radio frequency energy or we move M magnets near the loose pair lead wires, do we pick up a, we absolutely will pick up a signal which one is closer the red one. In this case, the blue one is further away in general, the f the amount of signal pick up will decrease with the one over the square of the distance. So it decreases dramatically. The further away you get from this energy source. So what do we amplify our amps? The difference? So something big minus something small still leaves something, right? So that signal will be picked, that error signal, that noise signal will be picked up in our wires. Here is a ribbon perle wire, which one is closer, the blue one, the red one is further away. But if they're very close together, so the difference will be smaller. Now, here's a twisted pair lead wire will they still pick up a signal? Yes, they will. But which wire is closer at this point? I was, I assume you guys can see my cursor, can you? Yeah. OK. Here at this point, the blue wires closer at that point, the red wire is closer at that point. The blue wire is closer at that point, the red wire is closer. So on average, the blue wire and the red wire are picking up the exact same noise signal. So the difference is zero. So when you summarize loose pair lead wires are going to pick up a lot more than a ribbon pair lead wire, which is gonna pick up more than a twisted pair lead wire. So that same thing applies for dangerous current as well, whether it's the Bovi, whether it's the radio frequency pulse coil from the MRI. And one of the best things that we can ever do, and I'm doing a presentation in April on, on uh electromagnetic aspects of electrode la layouts. And I, that, that was where all these movies came from is I, I did these movies just to show these things and lo and behold, the most powerful thing I could ever do is just show the movie and then everybody sees the example. But uh the best thing you can ever do for these dangerous radio frequency energies is to bundle twist, uh grade whatever you're recording lead wires together, which is different than so uh if II I know there are probably other questions. So what you guys for anybody has questions to speak up. Yeah, I got a question. This is not great. I why do we put these electrodes, these isolated ground in quote electrodes on people then? What are they actually doing? That's a really good question. And I was actually gonna show that. Um what the heck are they for then, right? Can everybody see this? Yes. OK. Uh Here guy and a girl out on canoes. Um And uh they want to, they want to talk but they can't because the waves, they're seeing the waves differently. Well, if they're together in the troughs and the peaks, they can make eye contact, they can actually communicate. They're seeing the waves at the same fashion. Grounding is like that. Oh, I'm sorry, I went in reverse. Uh Grounding is like that it ties the canoes together so that they see the waves, the noise the same without our ground electrode applied electrical noise at the amplifier is different than electrical noise. At that point on the patient where the ground is plied with our ground electrode applied, it ties the two together so that they see the exact same noise. The point on the patient where you connect that isolated ground wire then becomes electrically the identical spot as the inside of the isolated amplifiers. So if you've got no a a noisy spot on the patient, it is now the exact same noisy spot inside of the amplifiers and it is more common. So, so essentially the two see the same thing together and ideally it decreases artifact, it doesn't do anything to get rid of that dangerous current and take it back to the water pipe down in the basement. The reason that we no longer have that earth ground and which served a very good safety purpose. It took dangerous currents through the water pipe down to the ground, but it also introduced the abi the capa the possibility of ground loops like the person who just mentioned about the surge in, in their equipment when they go out and do the um I guess the uh mobile eegs, if you had earth ground on your equipment, the situation you described would absolutely be dangerous. But since you don't have um earth ground on your equipment, it's not the downside is that, that your this ground electrode we use serves absolutely no, no role in, in giving a pathway for dangerous currents to flow. So there's pros and cons of not having the, the earth ground. OK. Any other questions we probably shouldn't be calling them ground electrodes, then it's just confusing to people. It's absolutely confusing. It drives me absolutely crazy if we need to call them commons. Uh often times on the equipment it says common instead of grams. Yeah. But I think it's uh that would be like trying to swim against the current, you know, because everybody knows that it's a ground electrode, you know. So it's kind of like uh uh if you start calling it something else, everybody's gonna go. What are you talking about? Let's see. What do you mean? It's terrible. Thank you so much. This was great. Hey, it was such, it's really weird to not to not have any feedback at all while I'm sitting there. It's like I'm sitting in my office and I'm just sitting all by myself. It's perfectly quiet and you're sitting there going, are these people even out there? They are and they're all over the country. It's, it's really interesting and then this will live on as a recording and even more people will have access to it. So, and, and uh Bret, if you want to expand this and add some more things, that'd be great. You know, we'll just take that recording and plug it in. So, thank you so much, Brett. This was wonderful. You always do such a great job with animation and you're so good at, at making something very complex, very simple and easy to understand, which I really appreciate. Will those videos make your checks in the mail?