PARKS Flo-Lab User manual

APPENDICES

TECHNICAL ARTICLES

BASIC OPERATING INSTRUCTIONS

USE OF THE PENCIL PROBE IN THE DIAGNOSIS OF ARTERIAL DISEASE IN THE LIMBS

1. THE PROBE

The probe consists of two crystals; one for transmitting the ultrasound waves and the other for
receiving the reflected waves. If either crystal is damaged, the probe will not work properly or
will not work at all. The crystals are covered by a material that is vulnerable to attack by ECG
paste or cream. Therefore, DO NOT use ECG paste as the contact medium between the skin
and the probe. Use AQUASONIC or any gel made for ultrasonic physical therapy equipment. In
an emergency use any surgical jelly or lubricant, even petroleum jelly or mineral oil. Remove
the gel after use with a soft tissue. If you should find the probe with dried gel on it, wash it off
under running water. Do NOT scrape off the gel because you may damage the coating over

the crystals. Do NOT autoclave the probe.

2. POSITION OF THE PROBE

Invariably, people not accustomed to our probe use it incorrectly. The probe we furnish is
different from that of the other manufacturers and is used differently. If you hand someone
the probe and say “Here, try it for yourself”, they will almost always put it over their radial
artery and place the probe perpendicular to the artery—and perhaps with no coupling gel.
Many people have tried to compare our Doppler with other makes by this method. Keep in
mind that you are not buying a Doppler for use on the radial artery, but for use on vessels
you cannot feel. The best testing ground is therefore in your particular area of interest.
We believe our instruments will permit you to find the vessels easier, let you hear the venous
sounds easier and follow the vessels better than any other device on the market, regardless
of price. But it takes some practice in order to be able to do this. We believe the arm is
a good and most convenient limb for you to learn on—to learn how to hold the probe
depending on the depth of the artery and vein. The area about 150 mm each side of the
elbow is a good place to start.

First, put some gel on the tip of the probe. The gel squeeze-bottle must be shaken downward
and then gently squeezed to get the gel to come out. Pile up about 7 mm of gel on the
probe, making certain there are no large air bubbles in the pile, because ultrasound does
not go readily through air. It needs a continuous conducting medium, and the gel is ideal.

Turn the VOLUME control fully down (counter clockwise) and turn the instrument on.
Gradually turn up the volume. You should hear a rumbling sound if you are holding the
probe. This is caused by the vibration of the gel due to tremor in your arm. Now place the
probe over an artery in the arm about half way between the elbow and the wrist. Tilt the
back of the probe toward the hand at an angle of about 45 degrees, making certain there is
gel in the pathway between the probe and the skin. Move the probe and the skin sideways
to try to find the center of the artery and the hissing noise at heart rate, which is the Doppler
sound for an artery. If the sounds you hear are more or less continuous, that is simply the
background noise of the instrument and it means that you are not over the artery. The
main energy of the beam is only about as wide as the crystals in the probe, so there isn’t
much room for error in aiming the probe. For this reason you must always search the area
of the artery and tilt the probe for best Doppler sounds.

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APPENDICES

TECHNICAL ARTICLES

BASIC OPERATING INSTRUCTIONS

When you are looking for deep arteries, or for small or obstructed arteries, you will have to turn
the VOLUME control near maximum. This also means that every time you move the head of
the probe you are going to get some pretty big thumping noises in the earphones. Therefore
you want to avoid moving the head of the probe with respect to the skin as much as possible.
That is why you place the probe over the area where you think the artery is and then you search
for the exact point by moving the skin with the probe and changing the angle of the probe with
respect to the skin. You might wonder why these big transient noises can’t be filtered. We do
limit their intensity, but we do not filter. The reason is that in the search for low-velocity blood
flow, such as in occluded arteries and in the veins, the pitch of the Doppler sounds associated
with the blood flow are very low. Any filtering to eliminate or minimize the sounds accompanying
movement of the probe would also reduce the response to low-velocity blood flow sounds, and
of course this is undesirable.

3. DIAGNOSIS OF ARTERIAL DISEASE

The Doppler method of diagnosing arterial disease of the limbs is only one of several good
methods. It is probably the most convenient and least expensive of the better methods. It
is only qualitative but can be made semi-quantitative by permitting you to make systolic
blood pressure measurements along the leg with the aid of a proper cuff and manometer.

The great sensitivity of the transcutaneous Doppler can cause a doctor or technician to
conclude improperly that an arterial pathway is open when it isn’t. Collateral flow around
an obstruction can be well-developed, especially in the thigh, and cause pulsatile blood to
flow in the distal arteries. Or a major artery may be narrowed, causing pulsatile flow distally.
These mistakes in diagnosis can be avoided almost entirely by simple means and a little
bit of experience. An experienced user of the Doppler can recognize the characteristic
sounds of open and obstructed arteries. Remember that Doppler sounds vary in pitch
(frequency) with the velocity of blood flow. When you hear the Doppler sound on a normal
artery and compare it with a normal arterial pulse-pressure wave, you will recognize the
sound of the dicrotic notch, the very fast rise time of the wave and perhaps a third sound
just before the onset of a new pulse wave. While the origin of these second and third waves
in the descending branch of a pulse wave may be in dispute, their absence in vessels distal
to an obstruction is not disputed. So a diagnostic rule is that whenever you hear the second
and perhaps third sounds of a pulse wave of a major artery, you can be sure the artery is
open proximal to the probe. Plethysmographic studies also show a delayed crest to the
wave, associated with a slower rise time to the wave when there is an obstruction proximally.
Though the Doppler is permitting you to hear velocity changes rather than true volume
changes, the correlation is good enough to be quite valuable diagnostically.

Now the opposite is not necessarily true—that when you can’t hear second and perhaps
third sounds the artery is obstructed proximally to the probe. In the digits and smaller
vessels the pulse wave is smoothed out more, especially when there is some
vasoconstriction. Now of course there are cases that are in doubt. If you cannot clearly
hear the second and third sounds (the third sound is frequently missing), compare with the
same artery on the other limb. If you find a radical difference in the sound of the Doppler,
both in pitch and in amplitude, you are justified in being quite suspicious of the patency of
the artery of the first limb you studied provided you are now fairly skilled at optimizing the
sounds.

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PARKS Medical Electronics, Inc. Aloha, Oregon U.S.A.

APPENDICES

TECHNICAL ARTICLES

BASIC OPERATING INSTRUCTIONS

Another thing you listen for is the relative clarity of the arterial wave. How well it stands
out from the background noise of the instrument and perhaps the venous flow adjacent to
the artery. Move the probe a little to each side of the artery to make this estimation. In a
normal person you will find that you can make the arterial pulse wave almost completely
separate from the venous sounds by positioning of the probe.

The way you really come to a final conclusion that the artery is obstructed proximal to the
probe is by measuring the systolic pressure at the ankle with an ordinary arm cuff. If you
want to measure pressure at other places on the leg you will need a special cuff, the bladder
of which encircles the limb. We sell such cuffs. The method is as follows:

Wrap the cuff around the ankle or slightly above it so you can get the probe on the
posterior tibial and hear the arterial sounds adequately. Inflate the cuff to a pressure
well above the patient’s arm pressure or at least 30 points above the pressure at which
the Doppler sounds disappear. Gradually reduce cuff pressure until you hear blood flow,
though the sound won’t be normal. At that point read the pressure to obtain systolic
pressure at the ankle. If you have doubts, center the probe on the artery and inflate
the cuff again. You can observe at what cuff pressure the blood flow stops and again
where it starts. Where it starts is normally used.

This procedure is very similar to taking pressure on the arm using a stethoscope. There
you are using sounds of turbulence or wall motion. Here we are sensing the flow of blood
under the cuff with a much more sensitive device. You can get a clear indication of systolic
pressures as low as 30 mm of Hg. The only problem is keeping the probe right on the
center of the artery while you are inflating and deflating the cuff. An aneroid manometer
mounted on the inflation bulb of the cuff is preferable. Tycos makes such a device and
perhaps others do too.

The possibility of misdiagnosing is greatly reduced by this method provided you make two
or more measurements and you are skilled at holding the probe in the right place and at
the right angle. A low pressure reading is quite reliable. On diabetics you may get readings
of 300 mm Hg or more, even though they have ulcers on their toes. These people with
end-artery disease studied plethysmographically with the mercury-in-silastic strain gage,
which we also make, will have quite large and normal looking pulsations in the toes. Their
arterial walls are sclerosed so badly sometimes that they will not compress with cuff
pressure.

The normal pressure in the ankles should be about the same as the systolic pressure in
the arm, or a little higher. If the ankle pressure is 30 mm Hg or more lower than the arm
pressure, an obstruction is almost certainly present. Normally one finds that people with
arterial obstructions have pressures of 100 mm Hg or less.

If you have a proper cuff you can take pressures in the same manner (with the probe at the
posterior tibial) just below the knee, just above it and at the top of the thigh. By measuring
systolic pressure (the pressure measurement is always where the cuff is, not where the
probe is) you will find radical differences between measuring sites if the obstruction is between
them or you will find that pressures at corresponding points on the two legs are quite different.
An exception is bilateral obstruction of the bifurcation of the abdominal aorta which may
give you fairly symmetrical pressures on both legs. Unfortunately you cannot use the
Doppler above the top of the thigh. The pressure measurements made on the thigh with a
narrow cuff will be clinically useful, though not accurate.

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APPENDICES

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Once you have determined that there is an obstruction it is often desirable to determine
just where it is. It is permissible to check at certain points provided you are quite familiar
with normal sounds—second and perhaps third sounds. Start at the top of the thigh and
listen for the normal arterial sounds. A little to one side you should hear venous flow varying
with respiration. The adjacent venous flow assures you that you are indeed listening to a
major artery. This is important because you can get beautiful sounds from a collateral that
is aimed toward your probe and giving a tremendous Doppler effect. But a collateral follows
a tortuous path and the venous sounds will not be found adjacent to it. If you have a little
problem hearing the vein (and you shouldn’t over big veins) give the leg a slight squeeze
distal to the probe to increase the velocity of the venous blood and make its pitch higher.
As you follow the superficial femoral artery down toward the knee you will lose the sound,
even on normals, in some parts of the path because of tendons or other anatomical
obstructions between the probe and the artery. You should be able to pick it up again
easily in the popliteal region. Your ear and concentration make a filter to extract wanted
information from background noise that exceeds anything that can be done electronically.
You can follow these small arteries distal to the knee and in some cases they can be followed
all the way to the ankle and beyond. Keep in mind that some people don’t have a dorsalis
pedis artery. If you are working on arteries in the foot, make sure they are dilated by immersing
the foot in a bucket of warm water for a few minutes. Some people are vasoconstricted most
of the time. They usually will dilate for a while after the immersion and in a few minutes be
constricted again. Also they usually do not have arterial disease.

If you want to quickly determine the efficiency of flow in the arterial system of the leg, pick
up the posterior tibial and listen for 2nd and perhaps 3rd sounds. If you hear them, and
you are sure you know the difference between normal and abnormal, go no further. If they
do not sound normal or there is doubt, make a blood pressure measurement and compare
it with systolic pressure on the other ankle and on the arm. To find the location of the
obstruction you can listen with the Doppler, or using a special cuff you can make blood
pressure readings farther up the leg. If the obstruction is in the iliacs you can note it by
the Doppler sound distal to the obstruction or by a much lower than normal blood pressure
at the top of the thigh as measured with the cuff and the Doppler.

4. PRE-OPERATIVE AND POST-OPERATIVE use of the Doppler is very important.

When the patient is on the table, measure systolic pressure at both ankles and record it.
After blood is again permitted to flow, measure
operated leg should be UP compared to the pressure in the other leg, the control. If it
isn’t, then it is pretty safe to assume something is wrong. On rare occasions a limb will
have such a high degree of reactive hyperemia that pressure will not be up and may even
be lower, but the leg will be hot. A large percentage of patients are blocked to some degree
before they get off the table. Blood-pressure measurements will give you an objective
evaluation of the surgery. Some surgeons use the pencil probe directly on the artery (using
sterile jelly for coupling) just distal to the repair. The characteristic of the flow sound is
important. If the runoff is inadequate an experienced ear can detect it and often correct
the cause on the table. You can also use Doppler and pressure measurements for follow
up, comparing pressures at both ankles with systolic pressure at the arm, measured either
with a Doppler or stethoscope.

both

pressures again. The pressure on the

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PARKS Medical Electronics, Inc. Aloha, Oregon U.S.A.

APPENDICES

TECHNICAL ARTICLES

TECHNIQUE OF EVALUATING CALF VENOUS DISEASE

The assessment of calf venous disease by Doppler ultrasound may be achieved with an accuracy
of up to 85% compared to venography when one is experienced with the technique. The status of
the calf veins can be assessed by listening with the Doppler at the posterior tibial vein at the ankle,
the popliteal vein, the superficial femoral vein, and the common femoral vein. The status of the calf
veins is determined by a combination of augmentation maneuvers when listening at these various
points.

NORMAL RESPIRATION FLOW SOUNDS

The Doppler is initially placed over the posterior tibial vein at the ankle behind the medial
malleolus. Generous amounts of acoustic gel must be used, and one must be careful to avoid
undue pressure with the probe which might result in obstruction of venous flow. Initially the
posterior tibial artery signal is elicited. The probe is then moved slightly to either side of the
arterial signal until the windstorm like venous signal is heard. Normally this signal should wax
and wane with respiration. In the presence of calf vein thrombosis, the signal may be more
continuous or there may be no audible signal present. If the feet are vasoconstricted, a venous
flow signal may not be heard until the venous velocity is increased by gentle compression of
the foot.

CHECKING COMPETENCY OF THE VALVES

Once the optimal venous signal is elicited, the calf is then compressed with the hand which is
not holding the probe. The fingers should be spread so that much of the calf muscle is
compressed. During this procedure, no venous flow should be heard. If venous flow signals
are elicited, this is a sign of deep venous valvular incompetence, usually secondary to old deep
vein thrombosis.

AUGMENTING VENOUS VELOCITY BY COMPRESSION

Next the calf is released and one should normally hear an augmentation of venous flow as blood
enters the previously decompressed calf veins. The magnitude and duration of the augmented
signal can be influenced by several factors including the temperature of the foot, the general
vasomotor tone of the patient and the presence or absence of venous thrombosis in the calf. It
is important to compare the augmentation signals in each foot. In vasoconstricted individuals
with cold feet, the posterior tibial venous augmentation may be very minimal but it should be
symmetrical. If there is good augmentation in one leg and poor augmentation in the other, the
latter leg is usually the site of venous thrombosis. Next, the common femoral and then the
superficial femoral veins are examined and the signals assessed for augmentation upon calf
compression. Calf-vein thrombosis will result in a decreased augmentation of the venous signals
at these sites. Similarly the popliteal vein should be examined. In general, the most sensitive
indicator of calf-vein thrombosis is a relative decrease in augmentation upon release of calf
compression with the probe positioned over the posterior tibial vein at the ankle. There are
certain conditions which will imitate calf-vein thrombosis. Such problems as subfascial
hematoma, a ruptured Baker’s cyst, extensive edema, or other conditions which cause increased
pressure on the calf veins may result in a decreased augmentation of flow during the
aforementioned maneuvers. Such conditions can be best diagnosed by a venogram if the
diagnosis is in question.

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