U.S. patent application number 12/717771 was filed with the patent office on 2010-06-24 for ultrasonic material removal system for cardiopulmonary bypass and other applications.
This patent application is currently assigned to Ceeben Systems, Inc.. Invention is credited to Jared Colin Blanton.
Application Number | 20100160846 12/717771 |
Document ID | / |
Family ID | 37802557 |
Filed Date | 2010-06-24 |
United States Patent
Application |
20100160846 |
Kind Code |
A1 |
Blanton; Jared Colin |
June 24, 2010 |
Ultrasonic Material Removal System For Cardiopulmonary Bypass and
Other Applications
Abstract
Devices, systems, and methods manipulate target materials within
fluids, and may be useful for removing microbubbles and other
materials from blood. Ultrasound or acoustic filtering waves may be
directed across a flow of blood, and differences in density between
the target microbubbles and the blood may enhance separation by
driving the lighter matter upward for removal from the blood
stream. A disposable acoustically transmissive conduit can
replaceably engage an ultrasound transmitter to facilitate
sterilization. Exemplary conduits have elongate lumen
cross-sections and an axial path resembling a portion of a Mobius
strip.
Inventors: |
Blanton; Jared Colin;
(Oakland, CA) |
Correspondence
Address: |
TOWNSEND AND TOWNSEND AND CREW, LLP
TWO EMBARCADERO CENTER, EIGHTH FLOOR
SAN FRANCISCO
CA
94111-3834
US
|
Assignee: |
Ceeben Systems, Inc.
Oakland
CA
|
Family ID: |
37802557 |
Appl. No.: |
12/717771 |
Filed: |
March 4, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11463121 |
Aug 8, 2006 |
7699799 |
|
|
12717771 |
|
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|
60711386 |
Aug 26, 2005 |
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Current U.S.
Class: |
604/6.08 |
Current CPC
Class: |
A61M 1/3627 20130101;
B01D 19/0094 20130101; A61M 1/363 20140204 |
Class at
Publication: |
604/6.08 |
International
Class: |
A61M 37/00 20060101
A61M037/00 |
Claims
1. A filter for separating a target matter from a fluid flow, the
filter comprising: a fluid conduit having an input for receiving
the fluid flow, an output, and a lumen defining a fluid flow path
from the input to the output; an ultrasound or acoustic transmitter
for transmitting ultrasound or acoustic waves; and a target matter
port in fluid communication with the conduit lumen, the transmitter
oriented so that the waves drive the target matter across the fluid
flow path toward the port.
2. The filter of claim 1, the fluid flow at the input comprising
the target matter and a biological fluid, the target matter being
less dense than the fluid, wherein transmitter is disposed below
the fluid flow path and the port is disposed above the fluid flow
path.
3. The filter of claim 2, wherein the fluid conduit has an upper
surface, the upper surface sloping, along the fluid flow path,
upward toward the port and then downward away from the port.
4. The filter of claim 3, wherein fluid path resistance across the
lumen is balanced.
5. The filter of claim 4, wherein the lumen defines an axis and at
least 180 degrees of axial twist along the flow path.
6. The filter of claim 4, wherein the conduit comprises a first
body, a second body, and a third body, each body having a channel
and sandwiched between a first end plate and a second end plate,
the channels together defining the lumen; the channel of the second
body defining the upper surface and at least a portion of a target
matter lumen; the first body disposed between the second body and
the first end plate, the channel of the first body coupling the
input to the channel of the second body with a 90 degree twist
therebetween; the third body disposed between the second body and
the second end plate, the channel of the third body coupling the
channel of the second body to the output with a 90 degree twist
therebetween.
7. The filter of claim 4, wherein axial twist extends along a
significant length of the lumen.
8. The filter of claim 1, wherein the fluid path comprises a
laminar fluid path.
9. The filter of claim 8, wherein a bifurcation couples a target
matter lumen to the lumen at the port, the bifurcation having an
acute bifurcation angle.
10. The filter of claim 1, wherein the conduit comprises a material
having an acoustic impedance sufficiently matching an impedance of
the fluid flow to inhibit reflection of the waves.
11. The filter of claim 1, wherein the transmitter is oriented so
that the ultrasound waves impinge on a lumen wall of the conduit at
an angle so as to inhibit reflection of the waves.
12. The filter of claim 1, wherein the transmitter is attached to a
structure having a receptacle, the receptacle removably receiving
the conduit so that the transmitter is acoustically coupled to the
lumen.
13. The filter of claim 1, further comprising a power source
coupled to the transducer, the power source applying an alternating
waveform to the transducer, the waveform having a curvature with a
plurality of changes in sign between a maximum amplitude of the
waveform and an adjacent minimum amplitude of the waveform.
14. The filter of claim 1, further comprising a power source
coupled to the transducer, the power source applying a waveform to
the transducer, the waveform having a frequency that varies during
driving of the target matter with the waves.
15. The filter of claim 1, wherein the target matter comprises gas
bubbles and the fluid flow comprises blood flow.
16. The filter of claim 1, wherein the lumen has an elongate cross
section with a first cross sectional dimension between adjacent the
transmitter and adjacent the target matter lumen, and a second
smaller cross sectional dimension transverse to the first cross
sectional dimension.
Description
CROSS-REFERENCES TO RELATED APPLICATIONS
[0001] The present application is a Divisional of U.S. Ser. No.
11/463,121 filed Aug. 8, 2006 (Allowed), which application claims
the benefit of U.S. 60/711,386 filed Aug. 26, 2005; the full
disclosures, each of which are incorporated herein by reference in
their entirety.
STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSORED
RESEARCH OR DEVELOPMENT
[0002] NOT APPLICABLE
BACKGROUND OF THE INVENTION
[0003] The present invention is generally related to devices,
systems, and methods for manipulating materials within and/or
separating materials from fluids. In exemplary embodiments, the
invention provides an acoustic or ultrasound filter for removal of
microbubbles or other target matter from a fluid, particularly for
target matter having acoustic impedances and/or densities which are
significantly different than that of the remaining fluid.
Separation of microbubbles and other matter from biological fluids
can be (for example) beneficial for removing microbubbles from
blood before introduction of the filtered blood into the patient
during cardiopulmonary bypass systems, when using cell-saver
systems that filter and return blood that might otherwise be lost
during surgery, for dialysis treatment, and the like.
[0004] A number of different types of treatments rely on external
processing of the blood of a patient. An example of external blood
processing is often included in heart surgeries that involve
cardioplegia, in which beating of the heart is temporarily halted.
During cardioplegia, pumping of the blood through the vascular
system, and re-oxygenating the blood can be performed outside the
patient's body by a heart-lung machine of a cardiopulmonary bypass
system. While the patient is relying on the cardiopulmonary bypass
system, the blood flows in a continuous stream from the patient,
through the heart-lung machine, and back into the patient.
Similarly, patients with compromised kidney function rely on
dialysis treatments in which the blood flows from the patient,
through the dialysis machine, and back into the patient.
[0005] In general, biological fluids that are to be introduced into
a patient are handled and processed with great care. This can be
relatively challenging during dialysis treatments, cardiopulmonary
bypass, and other procedures in which a stream of fluids are
removed from the body, processed outside the body, and reintroduced
into the body. Such treatments often involve filtration, gas
exchange, and the like, with the biological fluid passing through
pumps, tubing, filter media, and other artificial structures.
Bubbles of various sizes can be introduced into the biological
fluids by this processing. While removal of larger bubbles can be
relatively straightforward, it can be quite challenging to
effectively remove microbubbles from blood and other biological
fluids prior to introduction into a patient. Small particulates
(and other undesirable materials that are difficult to remove) may
also be inadvertently introduced into blood during processing.
[0006] While a variety of techniques have been proposed and/or
implemented for removal of microbubbles and other impurities from
blood and other biological fluids, many known filtration techniques
have generally been found to be less than ideal. Hence, it would
generally be desirable to provide improved devices, systems, and
methods for manipulation and/or separation of target materials from
within fluids, particularly from biological fluids. It would be
particularly desirable if these improved techniques were compatible
with existing biological fluid processing or even facilitated
improved biological fluid processing to enhance the safety and
efficacy of dialysis treatments, heart-lung machines, and the like.
Ideally, such improved techniques would not significantly increase
the complexity or cost of the existing blood (and other biological
fluid) processing systems, nor increase the difficulty in
sterilizing biological fluid processing systems.
BRIEF SUMMARY OF THE INVENTION
[0007] The present invention generally provides improved devices,
systems, and methods for manipulating target materials within
and/or separating target materials from fluids, particularly from
biological fluids. Embodiments of the invention may be useful for
removing microbubbles and other acoustically manipulatable (and
often embolizable) materials from blood, particularly for
treatments involving cardiopulmonary bypass, dialysis treatments,
and the like. When used for filtration of blood or other biological
fluids, embodiments of the invention may benefit from a mismatch of
acoustic impedance between the (and from differences in density
between) the target matter (such as microbubbles, microspheres,
microbeads, or the like) and the remaining biological fluids, with
exemplary embodiments employing waves of acoustic or ultrasound
energy sweeping upward across a stream of the biological fluid so
that acoustic filtering and gravity together drive a lighter target
matter upward for easy removal from the fluid stream. A disposable
conduit that is at least in part acoustically transmissive can
acoustically couple the fluid stream to an ultrasound transmitter,
facilitating sterilization of the system by replacement of the
conduit. An exemplary laminar-flow conduit has an elongate
cross-section, ideally with a height (in the upward direction
traveled by the propagating waves) which is significantly greater
than a width across the conduit. Deleterious reflection of the
waves can be inhibited by a sufficient match between the acoustic
impedance of the conduit material opposite the transducer and the
biological fluid, by controlling the angle at which the waves from
the biological fluid impinge on the conduit material, and the like.
An exemplary conduit in which filtration takes place has a path
resembling a portion of a Mobius strip, providing a balanced flow
resistance across the conduit lumen and allowing removal of the
target matter from an at least local maximum height within the
lumen.
[0008] In a first aspect, the invention provides a filter for
separating a target matter from a fluid flow. The filter comprises
a fluid conduit having an input for receiving the fluid flow, an
output, and a lumen defining a fluid flow path from the input to
the output. An ultrasound or acoustic transmitter can generate
ultrasound or acoustic waves. A target matter port is in fluid
communication with the conduit lumen. The transmitter is oriented
so that the waves drive the target matter across the fluid flow
path toward the port.
[0009] In many embodiments, the fluid flow at the input will
include the target matter and a biological fluid. The target matter
will often be less dense than the fluid, and the transmitter can be
disposed below the fluid flow path. The port may open to the lumen
from above the fluid flow path, allowing the less dense target
matter to be removed from the top of the biological fluid so that
gravity aids in separation and removal of the target matter.
[0010] The fluid conduit can have an upper surface which, in the
direction along the fluid flow path, slopes upward toward the port.
After passing the port, the upper surface may then slope downward
away from the port. Hence, gravity may further tend to urge
microbubbles and other low density target matter upstream and/or
downstream toward the port. Regardless of the orientation, an
elongate lumen cross-section may extending in the direction of the
wave propagation may enhance filter efficiency and/or
effectiveness.
[0011] The fluid path resistance across the lumen can be balanced
to facilitate separation. For example, the lumen may define a
portion of a Mobius-strip-like structure, having an axis that
includes at least 180.degree. of axial twist along the flow path.
This axial twisting (often again with an elongate lumen
cross-section) may be defined by channels in a stack of plates, by
twisting a flexible conduit about it axis, or the like. The fluid
path will preferably comprise a laminar fluid path, and the port
will be included within a bifurcation having an acute angle between
the target matter flow path (along a target matter lumen) and the
fluid flow path.
[0012] The conduit will often comprise a material having an
acoustic impedance that sufficiently matches an impedance of the
fluid flow to inhibit reflection of the waves when the waves from
the biological fluid impinge on the conduit. For example, the
conduit material may have a Rayles number that is within about 15%
of the Rayles number of the biological fluid, ideally being within
about 10% of the Rayles number of the biological fluid. Where the
biological fluid comprises blood, suitable materials for including
in the conduit may have an acoustic impedance of between about 1.2
MRayle and 1.7 MRayle, with exemplary materials comprising an
ultrasound probe head material, a polymethyl pentane such as TPx
(which may be commercially available from Mitsubishi Corp. of
Japan), HDPE, or UHDPE. Reflection of the waves may also be
inhibited by controlling the angle at which the waves from the
biological fluid strike the conduit, with exemplary embodiments
having waves striking the conduit at close to about 90.degree.,
such as between about 80 and 110.degree..
[0013] The transmitter may be attached to a structure having a
receptacle which removably receives the conduit, and which
maintains acoustical coupling between the transmitter and conduit.
While some embodiments may employ a fluid bath encompassing the
conduit and at least a portion of the transmitter and/or openings
in the conduit to directly expose the transducer surface to the
fluid flow, exemplary embodiments may rely on simple engagement
between a flexible conduit material and the transducer surface to
facilitate removal and replacement of the conduit so as to avoid
cross-contamination of sequential fluid flows and decrease the need
for costly sterilization. Such coupling may optionally be enhanced
by a gel at the interface between the transmitter and the conduit
material.
[0014] While a variety of standard wave forms might be employed to
sweep the target matter from the stream of fluid, exemplary
embodiments may employ non-standard complex waveforms to drive the
transmitter. For example, rather than a simple standard sign wave,
a square wave, a triangular wave, or the like, tailored waveforms
having multiple changes in curvature (such as a waveform that
undergoes a plurality of changes between a positive second
derivative and a negative second derivative) as the wave advances
between a minimum and maximum amplitude within a single cycle.
Waveforms generated by a less than 25% duty cycle (such as a
waveform generated by a 10% duty cycle) may also be employed.
Varying or sweeping of the ultrasound frequency may also be
employed to inhibit the formation and/or deleterious effects of
standing waves.
[0015] The target matter may comprise gas bubbles such as
microbubbles or the like, and the fluid flow may comprise blood
flow. Alternative embodiments may filter microspheres, polymer or
other beads, or the like from biological or other fluids, and/or
may manipulate these target tissues within biological or other
fluids.
[0016] In another aspect, the invention provides a method for
filtering a biological fluid. The method comprises flowing the
fluid along a fluid flow path. Target matter is driven from within
the flowing fluid towards a target matter port by directing
ultrasound or acoustic waves across the fluid flow path. The target
matter is removed from the fluid flow path through the port.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 schematically illustrates a cardiopulmonary bypass
system including an embodiment of a filter of the present
invention.
[0018] FIG. 2 is a side view showing an exemplary filter for the
system of FIG. 1.
[0019] FIG. 3 is a cross-sectional view within the filter of FIG.
2, showing gravity-assisted ultrasound waves driving microbubbles
upward within a conduit from a blood flow path.
[0020] FIG. 4 is a side view of an alternative embodiment of a
biological fluid filter for use in the system of FIG. 1.
[0021] FIGS. 4A and 4B are a prospective view and end view,
respectively, of the filter conduit structure of the filter of FIG.
4.
[0022] FIGS. 4C through 4G are side views showing the structures of
plates that can be stacked together to form the filter of FIG.
4.
[0023] FIG. 5 schematically illustrates a complex waveform having a
plurality of changes in curvature sign between adjacent maximum and
minimum amplitudes.
[0024] FIG. 5A schematically illustrates an alternative waveform
having a 10% energized pulse duty cycle for driving the ultrasound
transducer.
[0025] FIG. 6 schematically illustrates sweeping the driving
frequency of the transducer so as to inhibit the formation of
standing waves within the filtering conduit.
DETAILED DESCRIPTION OF THE INVENTION
[0026] The present invention generally provides improved devices,
systems, and methods for manipulating target materials within
fluids and/or separating those target materials from fluids.
Advantageous embodiments allow filtration of acoustically
manipulatable or low-density materials (such as bubbles,
microbubbles, microspheres, beads, microbeads, and/or the like)
from blood or other biological fluids. Exemplary embodiments use
acoustic or ultrasound waves to drive microbubbles across a flow of
blood within a conduit and towards a target matter removal port.
Hence, aspects of the invention may have applications for removing
gaseous bubbles or microparticulates during cardiopulmonary bypass,
dialysis treatments, cell savers blood scavenging and separation
for return to the patient during surgery, as a supplemental system
for catheters, during femoral artery to femoral artery (sometimes
referred to as "fem-fem") bypass procedures, during known or newly
developed blood filtration (including custom filtration)
treatments, and the like. Additional embodiments may be used for
filtration of other fluids, including medications or the like.
Still further alternative embodiments may be used during filtration
of other fluids, such as removal of microbubbles from industrial
fluids.
[0027] Referring now to FIG. 1, an exemplary cardiopulmonary bypass
system 10 may include a heart-lung machine 12 for pumping and
oxygenation of blood from a patient P. Blood from the patient P
enters the heart-lung machine, which generally operates under the
control of a controller 14. As a result of the processing of the
blood within heart-lung machine 12, the blood leaving the
heart-lunch machine may include gaseous microbubbles and/or other
embolized microparticulates.
[0028] Before the blood from heart-lung machine 12 is reintroduced
into patient P, the blood passes through a filter 16. Filter 16
generally makes use of acoustic or ultrasound waves to drive
microbubbles and/or particulates across a flow of the blood toward
a target matter removal port, with the waves being generated by a
transmitter energized by a driver 18 under the control of
controller 14. While schematically shown in FIG. 1 as being
separate from heart-lung machine 12, filter 16 may be incorporated
into heart-lung machine 12 of cardiopulmonary bypass system 10.
Alternatively, the individual components of heart-lung machine 12
may be separated into a variety of alternative fluid path
structures. Optionally, a sensor 20 determines the efficacy of
filter 16 and/or cardiopulmonary bypass system 10, providing
feedback signals to the processor 14 of the system.
[0029] Processor 14 will typically comprise digital and/or analog
data processing circuitry, often including the electronic hardware
and/or computer programming software. Suitable hardware may include
a general purpose personal computer, workstation, or the like, or
may include a specialized proprietary processor or processor board.
The hardware of processor 14 will often be combined with software
in the form of machine-readable programming instructions or code
for implementing one, some, or all of the methods described herein.
The code will often be embodied in a tangible media such as a
memory, a magnetic recording media, an optical recording media 22,
or the like, and/or may be transmitted to processor 14 as
electrical signals, optical signals, wireless data signals, or the
like. Data and code transmission may be implemented via a cable, an
Intranet, an Internet, a wireless network, or the like. Processor
14 will often have or be coupled to appropriate input and output
devices for communications between the processor and the user, such
as a keyboard, mouse, touchscreen display or other user interface
for communications with a user of cardiopulmonary bypass system
10.
[0030] Referring now to FIG. 2, an exemplary filter 16 includes a
conduit 28 held in place relative to an ultrasound transmitter 30
by a support structure 32. Conduit 28 includes an input end 34
coupled to an output end 36 by a lumen 38. Blood flows into input
end 34 from heart-lung machine 12, and flows out from output end 36
toward the patient P. The input and output ends may include
couplers such as Luer fittings or the like. Conduit 28 may comprise
any of a wide range of polymer or other materials, with lumen 38
optionally having one or more coatings to inhibit deleterious
interaction between the bloodstream and the surrounding conduit
material. Conduit 28 may, for example, comprise a cast, molded, or
extruded TPx, high-density polyurethane, or ultra high density
polyurethane.
[0031] Exemplary conduit 28 shown in FIG. 2 has a form that is
described herein as resembling a portion of a Mobius strip. In
general, the lumen within conduit 28 will promote laminar flow of
the bloodstream, at least adjacent ultrasound transmitter 30. Such
laminar flow can be promoted in a variety of different ways, such
as by providing appropriate luminal surface shapes for the Reynolds
number of the blood flow that will pass therethrough by providing
sufficiently smooth luminal surfaces, transitions, and the like.
The lumen adjacent transmitter 30 will typically have a height H
which is significantly greater than the luminal width, the height
typically being at least two times the luminal width, often being
at least four times the luminal width at the transmitter. The
exemplary Mobius filter structure has an axial twist of about
90.degree. between the inlet end 34 and transmitter 30, and another
axial twist of about 90.degree. between transmitter 30 and the
output end 36. This can help balance the flow resistance across the
lumen. Also, filter 28 will often be positioned so that an upward
orientation 40 of the lumen adjacent transmitter 30 helps urge
microbubbles toward a target filter matter port and associated
target matter lumen 42. By sufficiently aligning the direction of
the applied acoustic force upon the target matter with the
direction of the buoyant force on the target matter, separation can
be enhanced. Gravity forces on the target material may be opposed
to the buoyant force, and both drag and flow may be at least
partially perpendicular to the buoyant force. The exemplary Mobius
filter has an upper luminal surface that slopes upward prior to
adjacent transmitter 30, and then slopes downward after transmitter
30 (as can be understood with reference to FIGS. 2 and 3).
Alternative conduit shapes, cross sections, and flow paths may also
be used, including non-twisting, locally peaking channels.
[0032] In operation, the waves directed from transmitter 30 drive
microbubbles 54 upward and toward a target matter port 44 for
extraction from lumen 38 via a target matter lumen 42. Ultrasound
transmitter 30 may comprise any of a wide variety of commercially
available ultrasound transmitting structures, including transducers
having transmitting and receiving capabilities. One exemplary
transmitter comprises a 1'' diameter (optionally having a 2''
diameter) ceramic ultrasound transducer commercially available from
Channel Industries, Inc. of Santa Barbara, Calif. under the model
name Navy III.TM. 5800 PZT 1 MHz transducer. This exemplary
transducer may, for example, transmit ultrasound waves at 1 MHz or
less, with the effective size of the transmitting surface often
being less than the overall transducer size (the primary mode of
the transducer often comprising about the center 2/3rds of the
overall transducer radius). One MHz ultrasound energy may have a
wavelength of about 1.4 mm in blood, with lower wavelengths
generally providing better filtering performance. Driving such a
transducer at lower frequencies, such as at about 580 kHz, may
improve filtering effect, while altering, varying, and/or sweeping
the driving frequency can inhibit standing waves and improve the
overall capabilities of the filter. Relatively large transmitting
surfaces may transmit waves more uniformly across lumen 38,
inhibiting deleterious reflection of the waves by limiting an angle
at which the waves propagating through the lumen strike the luminal
wall of conduit 28. Deleterious reflection of the waves may also be
inhibited by sufficiently matching acoustic impedance of the
conduit material to that of the fluid within in the lumen. For
example, suitable materials for a blood filtering may have an
acoustic impedance in a range of from numbers of about 1.2 MRayle
to about 1.7 MRayle.
[0033] A variety of structures and approaches may be employed to
provide acoustic coupling between transmitter 30 and the blood flow
within conduit 28. In the exemplary embodiment, support 32 includes
a plurality of arms 46 that hold conduit 28 in position with the
conduit acoustically coupled to transmitter 30. Advantageously,
arms 46 of support structure 32 may replaceably hold conduit 28 in
acoustic engagement with transmitter 30. Specifically, inner
surfaces of the arms 46 may each define receptacles, with the
receptacles together sufficiently supporting and positioning the
conduit for use. Removal and replacement of conduit 28 between
treatment of different patients may help avoid cross-contamination.
Arms 46 may be, for example, movable relative to the conduit to
facilitate replacement of conduit 28 with a different conduit for
treatment of another patient. In other embodiments, the conduit may
deform sufficiently to be held by detents of the arms, the arms
being fixed. A wide variety of alternative receptacle surface
structures might also be employed, including structures which
support the conduit using fasteners (such as threaded fasteners or
the like) latches, or the like. Optionally, a fluid tank similar to
that described in U.S. Pat. No. 5,344,136, the full disclosure of
which is incorporated herein by reference, may enhance acoustic
coupling by including at least a portion of the transducer surface
and conduit in a fluid bath, although such coupling may instead be
accomplished without a fluid bath by direct engagement between
conduit 28 and transducer 30, by a gel at the conduit/transducer
interface, or the like.
[0034] Removal of microbubbles from the bloodstream within conduit
28 can be understood with reference to FIGS. 2 and 3. Waves 50
propagate through laminar flow 52 of the blood through lumen 38.
Aided by gravity, waves 50 drive microbubbles 54 upward across the
flow within lumen 38. Drawing the target matter through target
matter lumen 42 with a speed sufficient to roughly matching the
flow velocities at the entrance of the target matter lumen with
that of the flow in lumen 38 may help maintain laminar flow
adjacent target matter port 44. Laminar flow may also be maintained
by providing a relatively narrow bifurcation angle adjacent port 44
between the target matter lumen 42 and lumen 38. Sufficient
smoothing of the bifurcation and the like may also help maintain
the smooth laminar flow. The blood (or other fluid) continues to
flow as it is being filtered, and the filtering by waves 50 does
not expose the blood flow to a large filter media surface area that
might add to microparticulate embolization, generate additional
microbubbles, or the like.
[0035] Microbubbles 54 tend to collect between peaks of waves 50,
so that the microbubbles may be moved laterally across the
bloodflow path as the waves propagate. The wavelength and power of
waves transmitted by transmitter 30 will preferably be sufficiently
low to avoid cavitation or damage to the blood, and specific power
and wavelengths for a particular conduit may be determined by
appropriate parametric studies. Typical filters will have powers of
from about 20 to about 50 W, with frequencies of from about 400 kHz
to about 4.5 MHz. Transducers capable of handling 250 watts at 15
volts rms (or greater, optionally being 100 volts rms) and 10 amps
may be suitable for some embodiments. Including a suitable material
in the conduit where the waves strike the luminal wall can inhibit
reflections, as can maintaining the angle between the impinging
waves and the luminal surface sufficiently close to about
90.degree..
[0036] An alternative filter 60 can be understood with reference to
FIGS. 4 and 4A through 4G. Filter 60 again includes a conduit with
a lumen providing fluid communication between an input 62 and an
output 64. In this embodiment, the conduit comprises a series of
plates having channels therein, with the channels together defining
a lumen 66 when the plates are stacked together. Lumen 66 once
again follows a path 68 similar in form to Mobius strip, with the
luminal walls presenting an elongate, relatively thin cross-section
adjacent transmitter 30.
[0037] The lumen path 68 within filter 60 can be understood by
reviewing the individual channels of the plates from which the
conduit is formed (see FIGS. 4C-4G), and by comparing those
channels to the side, end, and perspective view of FIGS. 4, 4B and
4A, respectively. The conduit of filter 60 includes three plates
72, 74 positioned between two end plates 78, 80. Central plate 74
may also define the target matter lumen 82 and port 84. An opening
86 in each of the plates accommodates ultrasound transmitter 30. As
can be seen in FIG. 4A, ultrasound transmitter 30 may optionally be
acoustically coupled to the flow within the lumen by providing an
opening in the conduit.
[0038] Referring now to FIG. 5, the general characteristics of a
waveform which may enhance filtering efficacy when applied by
driver 18 to the ultrasound transmitter of filter 16 (see FIG. 1)
is schematically illustrated. The curvature of waveform 90 varies
between a positive curvature (second derivative of greater than 0)
and a negative curvature (second derivative of less than 0) a
plurality of times within a single cycle between a maximum
amplitude 92 and a minimum amplitude 94. An alternative waveform
which may enhance filtering efficacy is illustrated in FIG. 5A,
with the waveform here having a 10% duty cycle. Sign waves, square
waves, triangular waves, and other standard shapes may be used in
some embodiments, but not provide the same microbubble filtering
efficacy, even though waveform 90 may be generated without
providing true resonance in the driving circuit as is typically
desired for power circuits.
[0039] Referring now to FIG. 6, driving the transducer with a
frequency f which changes over time may inhibit the formation of
standing waves. Such standing waves might otherwise interfere with
filtering of target matter from the fluid flow. A variety of
changes, alterations, or variations to the frequency might be
employed, with the exemplary sweeping of the frequency comprising a
smooth and gradual change from about 50 kHz below an optimized or
desired filtering frequency Opt to about 50 kHz above the optimized
or desired filtering frequency. Each sweep may take between about
0.01 sec and about 50 sec. Incremental changes in frequency might
also be employed in other embodiments.
[0040] While the exemplary embodiments have been described in some
detail, by way of example and for clarity of understanding, those
of skill in the art will recognize that a variety of modification,
adaptations, and changes may be employed. For example, multiple
ultrasound filter stages may be used to decrease blood or other
filtered fluid loss. High density target materials might be
filtered from lower density fluids using gravity assistance by
positioning the target material port below the lumen. A wide
variety of other changes might similarly be made. Hence, the scope
of the present invention should be limited solely by the appending
claims.
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