First, let me appologize for posting the last email 3 times.
The first wast not posted within 4 hours, and I thought that the
electron flow was faster than that, and suspected that the message had
been blocked for inappropriate content, so fearing that oldtimers disease
would leave the point unmade (which would have been tragic), I resent.
Now on to the question: Bubble Study=Agitated Saline and Constrast Agents.
Agitated Saline, made by connecting 2 syringes via a 3-way stopcock and
pushing saline back and forth between the syringes a few times, then
diverting the liquid into a vein,
other IV fluids including X-ray and MR contrast agents,
AND ultrasound contrast agents such as Optison, Albunex and such
ALL enhance ultrasound echoes because they contain bubbles.
The bubbles in agitated saline are large, I'll guess that they are 20 to
200 microns in diameter (bigger than a red blood cell) so they don't pass
through the capillaries of the lung, and therefore, if there is no PFO
(right to left atrial shunt) or ventricular or other right to left shunt,
then if injected into the veins, they are not seen in the left heart
chambers or in the aarterial system. So, a PFO can pass large bubbles.
Agitated saline is needed in PFO evaluation (rather than Doppler or
seeing the gap in the intra-atrial septum because a PFO is usually not
large enough to produce a blood velocity jet that can be seen with
Doppler, either spectral or "color".
The bubbles in "ultrasound contrast agents" (EchoGen, SonoView, Albunex,
Optison, Echovist and such) are near 3 micons in diameter, smaller
than a red blood cell (7 or 8 microns in diameter). These small bubbles
do pass through the lung from the venous side to the arterial side, so can
be used to increase echoes from blood in the left heart and arteries. The
strength of ultraosund echoes from blood is 50 deciBels lower than vessel
walls and heart walls, that means that the echoes from blood are 1/100,000
of the echo strength from solid tissue. Contrast agents (agitated saline
or ultrasound contrast agents) increase that echo strength because they
are bubbles filled with air (or gas) and the ultrasound impedance
difference between the liquid blood plasma and the ir is very high.
Bubbles also oscillate when ecposed to ultrasound so the echoes not only
include the transmitted frequency, but also harmonics which are double,
tripple, quadruple .... of the transmitted ultrasound frequency.
The reason that agitated saline does not contain small bubbles is that
small bubbles are not stable, the surface tension becomes more important
as a bubble gets smaller, so the gas in the bubble is compressed by
surface tension when the bubble is small, and the gas is forced into
solution, causing the bubble to vanish.
There are two ways to make small bubbles last long: 1. use a gas that does
not easily dissolve in water (or blood plasma); fluorocarbons are less
soluble than air, so the contrast agents use fluorcarbons. 2. lower the
surface tension between the gas and the liquid using a surfactant or
"shell" or partial enclosure. Albunex uses albumen, other contrast agents
use sugars or other complex molecules. The use of an insoluble gas is not
Some of the manufacturers have talked about the contained gas, but not
about the surface material. During animal testing, some of the
surfactants were found to stay in the lung. When considering toxicity, it
is as important to consider the effects of the surfactant as the gas.
On Thu, 27 Sep 2007, Betty-Sue/Elizabeth wrote:
> Kirk, is agitated saline contrast what Dr Sanbro called a "bubble study" ? E
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