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Re: Displacement Current Revisited
On 04/02/99 11:52:22 you wrote:
>
>Original Poster: "j. Grissom" <johngd-at-bellsouth-dot-net>
>I haven't really followed this thread but I can add some hard facts to this
>aspect. You are correct that rectification is involved. Most any oxide,
>particularly aluminum oxide will rectify.
>
>A few years ago I was hired by plaintiff's attorneys as an expert witness to
>investigate something similar. A urologist had been blinded by a defective
>resectoscope (fiber-optic device used to do bladder and urinary tract
surgery).
>The device consisted of two major parts: the fiber optic telescope and the
>resection unit. The latter unit is simply a small stainless loop connected to
>an electrosurgical ("electrosurg") unit. A polyp is hooked by the loop and a
>pedal pushed whereupon an RF current cuts the polyp. The electrosurg unit is
>remarkably like a small solid-state tesla coil, making about 600 watts of RF
in
>the low hundreds of kilohertz and at perhaps 5000 volts. It provides either a
>pure carrier (surgery) or 60 hz AM modulated (coagulation).
>
>The company that made the scope made a louse resection unit and so they had a
>(literally) basement machinist make an anodized aluminum adapter to fit their
>scope to another brand of resector. During surgery, this assembly, about the
>size of a 1st grade pencil, is inserted through the penis (OUCH!) into the
>bladder. The bladder is irrigated with saline. The saline is returned
>through
>another tube in the scope. The aluminum adapter was defective and allowed
>irrigation solution to run down the shaft of the scope. The surgeon was
>cutting
>a polyp from the top of the bladder and so was looking up through the scope.
>Fluid trickled down the shaft and puddled in his eye. When he keyed the
>electrosurg unit, the RF flowed down the stream, into his eye,
>skin-effect-followed the eyeball until it hit the optic nerve whereupon it
blew
>the nerve apart. Instant blindness.
>
>In the lawsuit, the blinded Dr testified that when the RF hit him he jumped
and
>stumbled backward, testimony confirmed by nurses. The company's defense was
>that A) RF won't shock (true) and b) the optic nerve has no feeling (true), c)
>their electrosurg unit was free of DC (true) and thus there was no stimulation
>to cause him to jump backward. My job was to determine what made him jump.
>
>I determined that when the irrigation fluid flowed across the anodized
>aluminum,
>it formed a poor aluminum oxide rectifier. When the adapter in question was
>placed in contact with a container of saline and RF applied, several hundred
>volts of DC appeared. I demonstrated this in court and was not challenged in
>any serious manner by the defense's experts. (Through amazingly massive
>incompetence, including not cross-examining the other side's expert witness,
>the
>Doc's lawyers lost the case for him.)
>
>So yes, rectification capable of generating enough DC to shock is certainly
>possible in a strong RF field. Surely enough to diddle with a compass needle
>(I
>believe that's what this is about, isn't it?)
>
>Something possibly related is what I occasionally see in my shop when
>bombarding
>neon (passing high current from a pole pig through the newly made unit to heat
>and outgas it). If one electrode heats faster than the other, the one to get
>red hot first can act like a diode tube filament. The neon tube then acts
like
>a diode. This is apparent from the 60hz flicker (as opposed to 120 hz) from
>the
>tube and the unhappy growl coming from the pig when its core gets saturated
>from
>DC. I suppose this effect could be present in a static gap on a tesla coil
>too. Anyone observed it?
>
>John
>
>
List,
This is off the subject of displacement current revisited, so I will address
this
side topic just once since I have some familiarity with both medicine and law.
Modern electrosurgical generators fall into two categories. Unipolar and
bipolar.
I use both several times a week. The early machines were unipolar
"hyphricators"
and are amazingly similar to TCs. Modern generators are entirely solid state
and
have sensing circuits that monitor and control total power outout. Still they
will shock the *HELL* out of the operator on occasion. I have been shocked
unexpectedly by the unipolar on more than one occasion. Usually it's due to a
small pin hole in the latex surgical glove and you complete the circuit to
ground.
Invariably the instrument you're holding will involuntarily fly across the
operating room. The burns are not just skin effect, but are deep, painful and
take several weeks to heal. They are usually on the finger tips where you are
holding the instrument. These machines are designed to burn tissue, right.
Unipolar generators produce a modulated high frequency current that cuts, burns
or is a blend of both. High spiked currents cut. A broad waveform that has
more area under the integrated power waveform burns or coagulates. I suspect
the modulating waves are what cause the shock. In the unipolar set up RF
current from the instrument is alternating around an RF grounded patient. You
want to avoid putting yourself into the loop. %^-at-
The bipolar uses two electrodes at the operating tip of the instrument.
Current
passes through one electrode, the tissue and the opposite electrode. Although
patients are usually grounded for safety, the ground is not the return.
Bipolar
generators also produce a modulated high frequency current that cuts, burns
or is a blend of both. Most endoscopic surgical excison loops use bipolar.
Particurally when operating in a a fluid environment such as the urinary
bladder.
Unipolar shouldn't be used since it seeks RF ground through the path of least
reistance in the body. Scarey, huh!
While bipolar is generallly considered safer than unipolar there are still
other
dangers. RF capacitive coupling. If the instrument sheath that passes through
the body part is well insulated or the RF ground is defective, the dielectric
of
the insulated sheath will couple huge amounts of RF to the body parts around
the
sheath. In experimental testing I have seen RF coupled 1/2" sparks and searing
of beef tissue next to one of these insulated sheaths. The sheath must be
designed not to couple RF energy.
Most of these unfortunate patient or physician burns are due to human error.
The most common is inadequate, defective, or no RF ground. These can result
in death or massive tissue desruction. Another is use of the wrong type of
generator. Unipolar for bipolar, vise versa. And, capacitive coupling.
Al oxide rectification (discussed many times on this list) comes far down on
the list of the cause of this unfortnate urologist's injury. Without doubt,
his optic nerve served as the path of least resistance for RF ground return.
These injuries have been will studied and I'm very sure Al oxide rectification
isn't one of them.
>From what you say his lawyers were poorly prepared or just incompetent. There
is a theory in law called "res ipsa loquitor" -- "the thing speaks for itself".
If the urologist was using their equipment and at the time his optic nerve was
destroyed and nothing else was a known cause, then it's up to the
*manufacturer*
to prove it was not due to their negligence. Other than legal malpractice,
I sure there were other facts the jury took into consideration that we don't
know about.
To close the circle on this discussion, how does all this relate to Tesla
coiling? These newer solid state generators may produce an infinite variety
of modulated RF at a wide range of powers. I have considered using one to
drive a TC at various frequencies with different modulation. Specifically,
I've thought about driving a big tube coil. I have not seen any cheap ones
on the resale markets. I think all functioning units go overseas. If anyone
comes across a cheap one, grab it. It will afford endless hours of
experimentation.
RWW