Heart Attacks and Defibrillators

Posted by PITHOCRATES - May 29th, 2013

Technology 101

Moving Electrons from one Atom to another creates a Positively and a Negatively Charged Atom

Too much humidity can make one uncomfortable.  It can labor your breathing.  Make you sweat so much that you stick to everything.  Making it feel hotter than it is (it’s not the heat; it’s the humidity).  And play havoc with well-coiffed ladies.  As excessive humidity can straighten the finest curl.  That’s why we like the spring and fall.  When there are warm days without the humidity.  Winters, on the other hand, are just too cold.  And uncomfortable humidity-wise.  They’re not too humid.  But too dry.  Giving us dried and cracked skin.  Bloody noses.  And painful electrical shocks.  As anyone can attest to who has slid out of a car only to get a big static spark when they pushed the door close.

What causes that static electric spark?  When you slide your buttocks over the car seat to get out of the car you are charging a capacitor.  By stripping electrons away from atoms.  Leaving atoms with fewer electrons than protons.  Giving them a positive charge.  And atoms with more electrons than protons.  Giving them a negative charge.  Atoms prefer to be electrical neutral.  Which is why when we reach for that metal door those excess electrons jump the air-gap as soon as they can.  So both atoms can return to a neutral state.  Until the next time we drag our buttocks across the seat.

These electric discharges can be painful.  And annoying as they scare the bejesus out of you when you’re not expecting it.  But this is not all that capacitors do.  As it turns out this charging ability has a lot of uses.  They are in pretty much every piece of electrical and electronic equipment we use.  We use them to condition power.  For power factor correction.  Signal processing.  Noise filters.  Tuned circuits (as used in a radio dial to tune in a station).  And energy storage.  Which is what we do when we drag ourselves across a car seat.  We’re storing energy that we discharge later.  In a car it just annoys us.  But it can act like a temporary battery when we change the batteries in something with a volatile memory.  So we don’t lose the songs on our MP3 player when we change the batteries.  And the energy they store can even save lives.

A Defibrillator sends an Electric Charge through an Irregularly Beating Heart to Shock it back into Rhythm

In the movie The Matrix the machines took over the world.  And used humans as batteries to power their machines.  Because a human is a little like an electrical battery.  It creates electricity that operates the human body.  For the human body is controlled by electrical impulses sent along our nervous system.  These electrical impulses even make our hearts pump.  The heart itself is ‘wired’ to transmit this pulse in a delayed mode to the various tissue in the heart.  First a pulse contracts the two top chambers (atria).  This contraction empties the blood they hold into the two bottom chambers (ventricles).  Then after a delay that same pulse contracts the ventricles.  Pushing the blood out and through the body.  When a doctor looks at an EKG he or she can see how that pulse propagates through the heart.  And determine if it’s healthy (showing a normal sinus rhythm).  Or if there was some cardiac event that has altered the normal sinus rhythm.

If a heart doesn’t have a normal sinus rhythm it can lead to cardiac arrest (i.e., a heart attack).  An arrhythmia (irregular heartbeat) can be a fast heartbeat.  A slow heartbeat.  Or it may be an irregular heartbeat.  Which is due to abnormal electrical activity in the heart.  And can lead to ventricular fibrillation.  Where the muscles don’t contract in a coordinated fashion with the proper delays propagating through the heart tissues to pump the blood.  But instead contract without this coordination.  Causing the heart muscles to quiver instead.  If this continues more than a few seconds the heart may stop.  With an EKG showing a flat line.  With no blood flowing organs begin shutting down.  Causing irreversible damage.  And if a normal sinus rhythm isn’t restored within 90 seconds once a person goes into v-fib the chance of survival from this cardiac event are pretty much zero.

In the movies and on television when a patient goes into v-fib they sometimes show the patient flat-lining when they rush in the crash cart.  They rub gel on the paddles of a defibrillator.  Yell ‘clear’ and shock the patient.  Sometimes with the patient jerking wildly from the jolt from the paddles.  They may do this a couple of times until they hear the flat-line begin beeping again in a sinus rhythm.  It doesn’t really happen like that, though.  If a person is flat-lining a jolt from a defibrillator won’t bring them back.  Some medicine shot into the heart and chest compressions might.  But not an electric shock.  The use of a defibrillator sends an electric charge through a heart beating with an irregular rhythm to shock it back into a normal rhythm.  Sort of like banging on an electronic device to get it working properly again.  With the physical shock perhaps jiggling a loose component back into connection with something.  It can sometimes make the device work again.  But it won’t make it work if the cord is unplugged or if the batteries had been removed.

Portable Defibrillators have a Charged Battery that Charges a Capacitor

Early defibrillators were AC devices that plugged into a wall outlet.  They had a big transformer to step up the voltage.  But they were big and bulky and difficult to move around in a crowded room.  And they didn’t work that well.  Rarely pulling a patient out of v-fib.  And sometimes damaged the heart tissue as much as the heart attack.  In 1959 the AC defibrillator was replaced with one using charged capacitors.  This is the type we see in the movies and on television.  And use in real life.

If a patient goes into cardiac arrest they set the charge level for the given arrhythmia.  As the capacitors charge the person who will use it removes the paddles while someone else applies an electrically conducting gel to the paddles.  The person then places the paddles on the patient with force to ensure a good electrical connection.  And waits for the unit to finish charging.  Once charged anyone working on the patient breaks any contact they have with the patient so they won’t get shocked, too.  When everyone one and everything is clear the person will focus on the EKG for the appropriate point in the rhythm to press a button that discharges the capacitors.  Causing the stored energy to flow from one paddle to the other through the heart.  To reset the arrhythmia into a normal sinus rhythm.

Time is critical in surviving a heart attack.  So using a defibrillator as soon as possible increased a person’s chances of surviving from a heart attack.  Making defibrillators portable allowed paramedics to use them in the field.  Before they got the patient to a hospital.  These portable units have a charged battery that charges a capacitor.  Electronics and computer controls even allow ordinary people to use an automated external defibrillator (AED).  You will see AEDs in crowded areas like airports, shopping malls, casinos, etc.  Anywhere a large concentration of elderly men (the most likely to suffer cardiac arrest) may congregate.  This device often triggers a security alarm when removed to alert first responders.  Someone who witnesses a person suffering a heart attack can follow automated voice instructions from the AED and hook it up on the patient.  The AED will analyze the arrhythmia.  Set the appropriate charge level.  But usually requires someone to press a button for the shock.  To give everyone a chance to get clear from the person before the capacitor discharges its energy.  Because if they are in contact with that body when that charge hits it they may have more than a bad hair day afterwards.  Perhaps even sending their own heart into arrhythmia.  As this shock will be nothing like the one they get after sliding out of a car on a dry winter’s day.



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