U.S. patent application number 10/820169 was filed with the patent office on 2004-12-09 for implantable arteriovenous shunt device.
Invention is credited to Faul, John L., Kao, Peter N., Nishimura, Toshihiko, Pearl, Ronald G..
Application Number | 20040249335 10/820169 |
Document ID | / |
Family ID | 33299817 |
Filed Date | 2004-12-09 |
United States Patent
Application |
20040249335 |
Kind Code |
A1 |
Faul, John L. ; et
al. |
December 9, 2004 |
Implantable arteriovenous shunt device
Abstract
A long-term implantable arteriovenous shunt device is provided
that can be used as a therapeutic method. The shunt device is
implanted between an artery and a vein, preferably between the
aorta and the inferior vena cava. The shunt device decreases the
systemic vascular resistance and allows a blood flow rate through
the shunt device of at least 5 ml/min after the implantation. The
blood flow rate could be controlled either via an open loop or a
closed loop control means. The shunt device could also be a
self-adjustable shunt device to self-adjust its structure to
control the blood flow rate through its lumen. Based on the effects
of the shunt device to the respiratory, cardiac and circulatory
system, the implantable shunt device could be beneficial as a
therapy to patients with problems or conditions related to these
systems.
Inventors: |
Faul, John L.; (Stanford,
CA) ; Nishimura, Toshihiko; (Menlo Park, CA) ;
Kao, Peter N.; (Palo Alto, CA) ; Pearl, Ronald
G.; (Palo Alto, CA) |
Correspondence
Address: |
LUMEN INTELLECTUAL PROPERTY SERVICES, INC.
2345 YALE STREET, 2ND FLOOR
PALO ALTO
CA
94306
US
|
Family ID: |
33299817 |
Appl. No.: |
10/820169 |
Filed: |
April 6, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60461467 |
Apr 8, 2003 |
|
|
|
Current U.S.
Class: |
604/9 ;
623/1.24 |
Current CPC
Class: |
A61M 1/3655 20130101;
A61M 2230/205 20130101; A61M 2230/30 20130101; A61B 5/026 20130101;
A61B 2017/00252 20130101; A61B 2017/1139 20130101; A61M 2230/06
20130101; A61B 2017/1107 20130101; A61M 1/3653 20130101; A61F 2/06
20130101; A61M 2230/202 20130101; A61B 2017/1135 20130101; A61B
17/11 20130101; A61M 5/1723 20130101; A61M 5/14276 20130101 |
Class at
Publication: |
604/009 ;
623/001.24 |
International
Class: |
A61F 002/06 |
Claims
What is claimed is:
1. A therapeutic method for a human, comprising: decreasing the
systemic vascular resistance by having for a long-term period an
implantable arteriovenous shunt device between an artery and vein
of said human, said shunt device having a blood flow rate through
said shunt device of at least 5 ml/min after said implantation.
2. The method as set forth in claim 1, wherein said artery is an
aorta and said vein is an inferior vena cava.
3. The method as set forth in claim 1, wherein said method is a
respiratory or cardio-respiratory therapy.
4. The method as set forth in claim 3, wherein said respiratory or
said cardio-respiratory therapy is based on an increase of the
partial pressure of O.sub.2 dissolved in the arterial blood plasma,
an increase of the hemoglobin O.sub.2 saturation in arterial or
venous blood, or an increase of the O.sub.2 concentration in
arterial or venous blood.
5. The method as set forth in claim 1, wherein said method is a
cardiac therapy.
6. The method as set forth in claim 5, wherein said cardiac therapy
is based on an increase of the cardiac output.
7. The method as set forth in claim 1, wherein said method is a
circulatory therapy.
8. The method as set forth in claim 7, wherein said circulatory
therapy is based on a decrease of the pulmonary arterial blood
pressure, a decrease of the systemic arterial blood pressure, a
decrease of the systemic systolic pressure or a decrease of the
systemic diastolic pressure.
9. The method as set forth in claim 1, further comprising
controlling said blood flow rate through said shunt device at a
blood flow rate level or range.
10. The method as set forth in claim 9, wherein said controlling
further comprises sensing and using physiological parameters,
wherein said physiological parameters are blood pressure, heart
rate, cardiac output, paO2, O.sub.2 saturation, O.sub.2 saturation,
mean systemic arterial pressure or mean systemic venous
pressure.
11. The method as set forth in claim 1, further comprising
self-adjusting said blood flow rate through said shunt at a
predetermined blood flow rate level or range by having said shunt
device capable of self-adjusting its cross sectional area or its
length, or both, as a function of the pressure difference across
said shunt device.
12. The method as set forth in claim 1, wherein said shunt device
is implantable via an open surgical procedure, a minimally invasive
surgical procedure, or an intravascular procedure.
13. An apparatus for therapy in a human, comprising: a long-term
implantable arteriovenous shunt device between an artery and a vein
in said human to decrease the systemic vascular resistance, wherein
the cross sectional area and the length of the lumen of said shunt
device are selected to having a blood flow rate through said shunt
device of at least 5 ml/min after said implantation.
14. The apparatus as set forth in claim 13, wherein said artery is
an aorta and said vein is an inferior vena cava.
15. The apparatus as set forth in claim 13, wherein said cross
sectional area is in the range of about 19 mm.sup.2 to about 750
mm.sup.2
16. The apparatus as set forth in claim 13, wherein said length is
in the range of about 2.5 mm to about 15 mm.
17. The apparatus as set forth in claim 13, wherein the radius is
in the range of about 2.5 mm to about 15 mm.
18. The apparatus as set forth in claim 13, further comprising a
control means to control said blood flow rate through said shunt at
a blood flow rate level or range.
19. The apparatus as set forth in claim 18, wherein said control
means comprises one or more sensors to sense said blood flow rate
or the pressure difference across said shunt device.
20. The apparatus as set forth in claim 18, wherein said control
means comprises one or more flow control elements.
21. The apparatus as set forth in claim 13, wherein said shunt
device is a self-adjustable shunt device to self-adjust its cross
sectional area or its length, or both, as a function of the
pressure difference across said shunt device to automatically
control said blood flow rate through said shunt at a predetermined
blood flow rate level or range.
22. The apparatus as set forth in claim 13, wherein the inner wall
of said shunt device has a coating to prevent clot formation or
atheroma formation.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is cross-referenced to and claims priority
from U.S. Provisional Application 60/461,467 filed Apr. 8, 2003,
which is hereby incorporated by reference.
FIELD OF THE INVENTION
[0002] The present invention relates generally to medical devices
and methods. More particularly, the present invention relates to
non-cardiac devices and methods that provide a fistula or lumen
between the arterial system and venous system.
BACKGROUND
[0003] Chronic obstructive pulmonary disease affects millions of
patients in the United States alone. The present standard of care
is oxygen therapy, which requires a patient to remain near a
stationary oxygen source or carry a bulky portable oxygen source
when away from home or a treatment facility. It is easy to
appreciate that such oxygen therapy has many disadvantages.
[0004] Lung reduction surgery has recently been proposed for
treating patients with chronic obstructive pulmonary disease. Such
surgery, however, is not a panacea. It can be used on only a small
percentage of the total patient population, requires long recovery
times, and does not always provide a clear patient benefit. Even
when successful, patients often continue to require supplemental
oxygen therapy.
[0005] For these reasons, it would be desirable to provide improved
approaches, including both devices and methods, for treating
patients suffering from chronic obstructive pulmonary disease. It
would be desirable if such devices and methods were also useful for
treating patients with other conditions, such as congestive heart
failure, hypertension, hypotension, respiratory failure, pulmonary
arterial hypertension, lung fibrosis, adult respiratory distress
syndrome, and the like. Such devices and methods should provide for
effective therapy, preferably eliminating the need for supplemental
oxygen therapy in the treatment of chronic obstructive pulmonary
disease. After the procedures, such devices and methods should
optionally be adjustable so that the degree of therapy is
responsive to the patient's needs at any particular time. At least
some of these objectives will be met by the invention described
hereinafter.
SUMMARY OF THE INVENTION
[0006] The present invention is a long-term implantable
arteriovenous shunt device that can be used as a therapeutic
method. The shunt device is implanted between an artery and a vein,
preferably between the aorta and the inferior vena cava. The shunt
device is implanted for a long-term period of at least 6 weeks and
the implantation could be established via an open surgical
procedure, a minimally invasive surgical procedure, or an
intravascular procedure.
[0007] The objective of the shunt device is to decrease the
systemic vascular resistance and allow a blood flow rate through
the lumen of the shunt device of at least 5 ml/min after the
implantation. The cross sectional area (or radius) and the length
of the lumen of the shunt device are selected to having such a
blood flow rate, with the cross sectional area in the range of
about 19 mm.sup.2 to about 750 mm.sup.2, the length in the range of
about 2.5 mm to about 15 mm, and the radius in the range of about
2.5 mm to about 15 mm. In one embodiment, the inner wall of the
shunt device has a coating to prevent clot formation or atheroma
formation.
[0008] In some situations it might be desirable to control the
blood flow rate. Therefore, the present invention includes a
control means to control the blood flow rate through the shunt at a
desirable blood flow rate level or range. The control means could
be as simple as an on/off mechanism (or switch), or could be more
sophisticated by regulating the rate of flow ranging from either an
open loop control or a closed loop control with feedback provided
by physiological parameters. For each level of sophistication, the
control means could include a controller (ranging from a switch to
a decision algorithm), one or more flow control elements that
control the rate of flow through the lumen, and/or one or more
sensors to provide feedback to a controller. Examples of
physiological parameters that could be sensed or measure are blood
pressure, heart rate, cardiac output, paO.sub.2, O.sub.2
saturation, O.sub.2 saturation, mean systemic arterial pressure or
mean systemic venous pressure.
[0009] In an alternate embodiment, the shunt device could a
self-adjustable shunt device to self-adjust its cross sectional
area or its length, or both, as a function of the pressure
difference across the shunt device. The self-adjustable shunt could
then automatically control the blood flow rate through the shunt at
a predetermined blood flow rate level or range. The material of
such a self-adjustable shunt device would then have expansion and
contraction features to change the cross sectional area or the
length, or both.
[0010] The reduction of systemic vascular resistance and
(controlled) blood flow through the shunt device from the arterial
system to the venous system has some important consequences that
could benefit various kinds of patients. These consequences are
related to respiratory, cardiac and circulatory effects. For
example, the method could be a respiratory or cardio-respiratory
therapy based on an increase of the partial pressure of O.sub.2
dissolved in the arterial blood plasma, an increase of the
hemoglobin O.sub.2 saturation in arterial or venous blood, or an
increase of the O.sub.2 concentration in arterial or venous blood.
Accordingly, patients with respiratory problems could benefit from
the consequences as a respiratory or cardio-respiratory therapy. In
another example, the method could be is a cardiac therapy based on
an increase of the cardiac output. Accordingly, patients with
cardiac problems could benefit from the consequences as a cardiac
therapy. In yet another example, the method could be a circulatory
therapy based on a decrease of the pulmonary arterial blood
pressure, a decrease of the systemic arterial blood pressure, a
decrease of the systemic systolic pressure or a decrease of the
systemic diastolic pressure. Accordingly, patients with circulatory
problems could benefit from the consequences as a circulatory
therapy.
BRIEF DESCRIPTION OF THE FIGURES
[0011] The objectives and advantages of the present invention will
be understood by reading the following detailed description in
conjunction with the drawings, in which:
[0012] FIG. 1 shows the concept of decreasing systemic vascular
resistance according to the present invention;
[0013] FIG. 2 shows an example blood flowing, with or without a
shunt device of the present invention, from a high resistance
arterial system with a high oxygen concentration to the low
resistance venous system with a low oxygen concentration;
[0014] FIG. 3 shows an example of shunt device positioned between
the aorta and inferior vena cava according to the present
invention;
[0015] FIG. 4 shows examples of shunt devices according to the
present invention;
[0016] FIG. 5 shows an example of shunt device with a control means
according to the present invention;
[0017] FIG. 6 shows an example of shunt device with a controllable
or self-adjustable mechanism according to the present
invention;
[0018] FIG. 7 shows an example of shunt device with a controllable
mechanism based on a smart material according to the present
invention;
[0019] FIG. 8 shows an example of a self-adjustable shunt device
according to the present invention;
[0020] FIG. 9 shows an example of shunt device with a means to
increase resistance to blood flow according to the present
invention; and
[0021] FIGS. 10-12 show additional information regarding some
physiological effects of an aorto-caval fistula in rats according
to the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0022] Blood flows from the heart via the arterial system AS to the
vasculature of the tissues from which it returns back to the heart
via the venous system VS as shown by system 110 in FIG. 1. Blood
returning to the right side of the heart is pumped to the lungs
where it binds oxygen (becomes oxygenated, or re-oxygenated) before
returning to the left side of the heart to be pumped to the body's
tissues via the arterial system. Blood flow experiences a
resistance from all of the systemic vasculature, which is referred
to as the systemic vascular resistance (SVR). SVR excludes the
pulmonary vasculature but when these two are combined it is
sometimes referred as total peripheral resistance (TPR). SVR is
determined by factors that influence vascular resistance in
individual vascular beds. Mechanisms that cause vasoconstriction
(reducing the caliber of a vessel) will increase SVR, and those
that cause vasodilation (increasing the caliber of a vessel) will
decrease SVR. The actual change in SVR in response to neurohumoral
activation, for example, will depend upon the degree of activation
and vasoconstriction, the number of vascular beds involved, and the
relative in-series and parallel arrangements of these vascular beds
to each other. Although SVR is primarily determined by changes in
blood vessel diameters, changes in blood viscosity will also affect
SVR.
[0023] The present invention decreases the SVR by having an
arteriovenous shunt device 130 implanted to shunt and re-circulate
blood from the arterial system AS to the venous system VS in system
120 as shown in FIG. 1. The re-circulated blood through shunt
device 130 bypasses the peripheral microcirculation and decreases
the SVR when one would compare system 110 with SVR.sub.0 to system
120 with SVR.sub.1; i.e. SVR.sub.1 is lower than SVR.sub.0. A
desired decrease of the SVR would be at least 5% after the
implantation of shunt device 130.
[0024] In general, shunt device 110 could be implanted between a
large (proximal) artery and a large (proximal) vein. The location
is selected to shunt and (quickly) re-circulate blood from the high
resistance arterial system with a high oxygen concentration to the
low resistance venous system with a low oxygen concentration as
shown by system 120 in FIG. 2. In a preferred embodiment,
implantation of shunt device 130 is between the aorta 310 and the
inferior vena cava 320, either proximal of the renal arteries, or
more preferably distal of the renal arteries, as shown in FIG.
3.
[0025] Blood flow through a lumen 230 of the shunt device 130
typically results from a pressure gradient between the blood in the
arterial system and the blood in the venous system, indicated by
the large P and small p in FIG. 2 (note different font sizes). The
blood flow rate through shunt device 130 after implantation should
be at least (about) 5 ml/min. While the pressure gradient between
the arterial and venous sides of the vasculature will generally be
sufficient to achieve and control the target volume of blood flow,
in some instances it may be desirable to utilize a control means or
self-adjustable mechanism to either maintain a level/range or
increase/decrease the blood flow rate (see also infra).
[0026] The reduction of SVR and (controlled) blood flowing through
shunt device 130 from the arterial system to the venous system has
some important consequences when system 110 (pre-implantation) and
is compared with system 120 (post-implantation). These consequences
are related to cardiac, circulatory and respiratory effects.
[0027] With respect to the cardiac effects, an important
consequence of decreasing the SVR is that the cardiac output
increases according to: 1 CO = MAP - CVP SVR
[0028] whereby CO is cardiac output, MAP is mean arterial pressure,
and CVP is central venous pressure. Since CVP is normally near 0
mmHg, the calculation is often simplified to: 2 CO = MAP SVR
[0029] Cardiac output is equivalent to the blood flow rate
according to:
CO=SV*HR
[0030] whereby SV is stroke volume and HR is heart rate.
[0031] When SVR decreases, MAP decreases to a smaller degree. The
decrease in MAP is due to a small drop in systolic pressure
(P.sub.systolic) and a larger drop in diastolic pressure
(P.sub.diastolic). P.sub.diastolic is dependent on the SVR whereby
a drop in SVR results in a drop in P.sub.diastolic. The pulse
pressure (P.sub.systolic-P.sub.diastolic) is then increased. For
instance, before implantation MAP could be 90 mmHg and SVR could be
18 dynes, which results in a CO of 5 liters per minute. SVR of 18
dynes is determined by dividing an SVR of 1440 dynes by a
conversion factor of 80. MAP of 90 mmHg is determined by using: 3
MAP P diastolic + 1 3 ( P systolic - P diastolic )
[0032] with an exemplary PP of 30 mmHg given a P.sub.systolic of
110 mmHg and P.sub.diastolic of 80 mmHg.
[0033] After implantation, SVR could for instance drop from 1440
dynes to 1000 dynes and with the conversing factor of 80 drop from
18 to 12.5. If blood pressure has a P.sub.systolic of 100 mmHg over
a P.sub.diastolic of 55 mmHg, then MAP is 70 mmHg; i.e. in this
example the P.sub.systolic could have dropped by 10 mmHg, but the
P.sub.diastolic could have dropped by 25 mmHg. Combining these
exemplary numbers would result in a cardiac output of 5.6 liters
per minute; i.e. 70 mmHg divided by 12.5.
[0034] With respect to the respiratory effects, an important
consequence of shunting arterial blood to the venous circulation
(such as the aorta to the inferior vena cava) is that blood with
high O.sub.2 content circulates to the venous blood system without
having the O.sub.2 extracted in tissue capillaries. The O.sub.2
"rich" arterial blood re-circulates to, and mixes with, the low
O.sub.2 concentration of the venous system. As a result, the blood
flowing through shunt device 130 increases the O.sub.2
concentration in the venous blood, which is illustrated by the
different (font) sizes of O.sub.2 in FIG. 2. The increase of
O.sub.2 concentration in the venous blood system leads to an
increase in the O.sub.2 concentration in the arterial blood in two
ways, which is also illustrated by the different (font) sizes of
O.sub.2 in FIG. 2. First, since the blood that is shunted does not
have O.sub.2 extracted by tissue capillaries, the blood returning
to the lungs has a higher O.sub.2 concentration after the creation
of the shunt than before. Second, O.sub.2 is carried in the blood
in two forms: (i) dissolved in arterial plasma, and (ii) bound to a
protein called hemoglobin that is contained in red blood cells.
Oxygen binds to hemoglobin with curvilinear kinetics, so that
O.sub.2 very efficiently binds to (and is carried by) hemoglobin at
high PaO.sub.2 (partial pressure of O.sub.2 in arterial plasma),
but when the PaO2 is low (in particular below a PaO.sub.2 of 60
mmHg), O.sub.2 is less efficiently bound to (or carried by)
hemoglobin. Since the amount of O.sub.2 that is bound to hemoglobin
is related to the PaO.sub.2, an increase in PaO2 will result in
greater binding of O.sub.2 to hemoglobin, and increased oxygen
carrying capacity.
[0035] With respect to circulatory effects, an important
consequence of decreasing SVR is related to the fact that the lungs
regulate their blood flow according to the O.sub.2 content. A low
O.sub.2 content in the small pulmonary arteries impairs blood flow
to the lung resulting in a high pulmonary pressure--a process
called hypoxic pulmonary vasoconstriction. Therefore increasing the
O.sub.2 content in the pulmonary arterial blood should decrease the
pulmonary arterial blood pressure. Other important circulatory
consequences, as described supra with respect to cardiac
consequences, are a decrease in systemic arterial blood pressure, a
decrease in systemic arterial systolic pressure and/or a decrease
in systemic arterial diastolic pressure.
[0036] As a person of average skill in the art would readily
appreciate, the different distinct effects could be beneficial to
patients with cardiac problems as a cardiac therapy, to patients
with respiratory problems as a respiratory or cardio-respiratory
therapy, or to patients with circulatory problems as a circulatory
therapy. An illustrative list of therapies is for instance:
[0037] Cardiac therapies. The shunt device of the present invention
could benefit patients with cardiac failure or patients who suffer
from a low cardiac output (congestive heart failure) by providing
an increased cardiac output.
[0038] Respiratory or cardio-respiratory therapies. The shunt
device of the present invention could benefit patients with
pulmonary arterial hypertension to lower pulmonary arterial blood
pressure, patients with heart and/or respiratory failure by
increasing arterial oxygen concentration, patients with chronic
obstructive pulmonary disease by increasing of blood oxygen
concentration.
[0039] Circulatory therapies: The shunt device of the present
invention could benefit patients with hypertension to lower
systemic arterial, systolic and/or diastolic blood pressure.
[0040] Other diseases or conditions that could benefit from the
present invention are, for instance, hypotension (by increasing
cardiac output), lung fibrosis, adult respiratory distress
syndrome, and the like.
[0041] The blood flow rate through the shunt device is preferably
at least 5 ml/min. In case the shunt device is a cylinder then the
parameters of the lumen of the shunt device that determine the
blood flow rate through its lumen can be determined with the
Poiseuille equation: 4 BFR = Pr 4 3 l
[0042] whereby the volume flow rate (BFR) is a function of a blood
with viscosity .eta., the pressure difference .DELTA.P across the
lumen of the shunt device, length l of the lumen of the shunt
device and radius r of the lumen of the shunt device as shown by
shunt device 410 in FIG. 4. One could also refer to the cross
sectional area CSA of the lumen of shunt device 410, which is in
case of a cylinder equivalent to .pi.r.sup.2. Generally speaking,
the shape of the lumen could be a circle, an oval or any other
shape as long as the requirement of blood flow is met.
[0043] In an illustrative example using the Poiseuille equation,
.DELTA.P could range from about 30 mmHg (in someone with a MAP of
40 mmHg and a venous pressure of 10 mmHg) to about 150 (in someone
with a MAP of 160 mmHg and a venous pressure of 10 mmHg). The blood
viscosity could be determined in a variety of ways that could for
instance be obtained from a paper by Johnston B M et al. (2004)
entitled "Non-Newtonian blood flow in human right coronary
arteries: steady state simulations" and published in J Biomechanics
37:709-720. With a viscosity of 0.0345P and a combination of a
radius of 3 mm and a length of 3 mm of the lumen of the shunt
device one would achieve a blood flow rate through the shunt of
over 5 ml/min. As a person of average skill would readily
appreciate, different combinations of radius and length could be
determined to achieve the desired blood flow rate. In general, the
length could range from about 2.5 mm to about 15 mm, and the radius
could range from about 2.5 mm to about 15 mm. For the length one
could determine a minimum length of e.g. 2.5 mm given an exemplary
wall thickness of a human adult aorta of about 1.5 mm and an
exemplary wall thickness of a human adult inferior vena cava of
about 1 mm. One could also express the lumen opening in terms of
cross section area, which could range from about 19 mm.sup.2 to
about 750 mm.sup.2.
[0044] The shunt device is preferably made from any biocompatible
material strong enough or sufficiently reinforced to maintain a
lumen that meets the desired blood flow rate. In one embodiment,
the shunt device is made of metal, preferably titanium, while in
other embodiments the shunt device could be formed from
conventional vascular graft materials, polytetrafluoroethylene
(PTFE), nickel titanium memory, elastic material, or the like. The
inner surface of the shunt device is preferably coated in whole or
in part to inhibit the formation of blood clots. The surface could
be coated with for instance polytetrafluoroethylene (Teflon.RTM.),
or similar coatings/products. The shunt device might also be coated
with antibiotic to prevent atheroma, infection, and/or
anti-proliferative or anticoagulant agents to prevent clot
formation in the lumen.
[0045] In a preferred embodiment, loosing the connection of the
shunt device with the artery and vein should be avoided. Different
techniques could be employed to provide such a secure connection.
For instance, for attachment of shunt devices formed from typical
fabric graft materials one could use sutures, staples,
biocompatible glues, or the like. In the case of metals and other
rigid materials, the shunt device could be formed with flared or
flanged ends, such as the umbrella or funnel device 424 (shown in
FIG. 4). Umbrella ends 424 are placed at opposite ends of a tubular
element 422 that form shunt device 420. Umbrella ends 424 are
positioned respectively inside the artery and inside the vein, and
the tubular element connects in between the artery and the vein. In
a different embodiment, umbrella ends 434 could be positioned more
or less perpendicular with respect to tubular element 432 as shown
in shunt device 430. The key idea is that the diameter of the
securing (connection) elements is larger than the opening in the
artery and vein thereby keeping the shunt device in place. The
securing elements could include a mechanism that unfolds when the
shunt device is in place and implanted in the artery and vein. The
art teaches different techniques and securing type mechanisms that
could be used in the present invention.
[0046] The shunt device(s) could be implanted in a variety of ways,
including the open surgical procedures, the laparoscopic and other
minimally invasive techniques, and the intravascular techniques
(where all or a portion of the shunt device is introduced at least
partially through the lumen of one of the blood vessels to be
shunted). The shunt device could also be implanted by, for
instance, a surgical procedure such as an aortic surgery. The shunt
device could further be implanted through interventional procedures
such as, for instance, by means of a catheter through the iliac
artery and guided by fluoroscopy. The shunt device could be
deployed over a guidewire (e.g. the Seldinger technique) and
assembled in the body through interventional radiology techniques
like the opening of an umbrella. All such surgical and
interventional techniques are well known in the art. It is
preferred to leave the shunt device implanted in the person for a
long-term period (at least 6 weeks, but most often for years).
[0047] In some cases it might be desired to include a control means
to control the blood flow rate with one or more flow control
elements, one or more controllers and/or one or more sensors. A
flow control element 520 could be placed in the shunt device 510 as
shown in FIG. 5. It could be placed at either end of the shunt
device or somewhere in between. In one example, the function of the
flow control element could be as simple as to have an electrically,
magnetically or mechanically open/close mechanism such as a switch
or one-way valve. Such an open/close element could also be a hook
with a lever or a gearshift. In another example, a controller 530
could be used to control the timing of opening/closing (e.g.
frequency and duration) or to control changes in blood flow rate.
Controller 530 could control flow control element 510 such as
one-way valve(s), pump(s) (positive displacement pump(s), rotary
pump(s), peristaltic pump(s), and the like), controllable
orifice(s) and the like. The flow control element could be
electrically charged using an internal battery (e.g. a lithium
battery; not shown) or by external power (not shown) using a
magnetic impeller, both of which are common techniques in the
art.
[0048] Yet another advancement of the control means for the shunt
device is to include one or more sensors 540 that provide feedback
to the controller 530. The figures show two sensors, however, the
present invention is not limited to two sensors and could be at
least one sensor that is implanted inside the shunt device, near
the shunt device, or inside or near the vasculature system. The
sensor(s) could also be placed outside the body. Sensors 540 could
sense (and/or measure) physiological parameter(s) in real time
either periodically or continuously. The selection of one or more
physiological parameters could be to reflect the condition of a
person or patient who is being treated. Examples of physiological
parameters that could be sensed with one or more sensors are blood
pressure, heart rate, cardiac output, paO.sub.2, O.sub.2
saturation, O.sub.2 saturation, mean systemic arterial pressure,
and/or mean systemic venous pressure. The controller could include
a decision method to determine appropriate action on the flow
control element. The controller could either be a stand-alone
implantable controller and/or could be operated from outside the
body. It might be useful to update the controller or change the
current controller settings; e.g. in cases when the controller
controls a set-value, a particular range or critical boundaries
(minima/maxima), or when the controller requires an upgrade of its
code.
[0049] The controller may select different criteria that are e.g.
dependent on the type of disease, condition and/or desired therapy.
In one example, the heart rate could be maintained at a reasonable
physiological range and not exceed the person's maximum heart rate.
The controller could have a target heart rate range of, for
instance, 80 to 140 beats per minute, more usually from 90 to 110
beats per minute. In another example, it might be desired to
increase cardiac output, partial pressure of O.sub.2 dissolved in
the arterial blood plasma (PaO.sub.2), the hemoglobin O.sub.2
saturation in arterial or venous blood, or the O.sub.2
concentration in arterial or venous blood. These increases could be
at least 5% compared to their value before implantation, except for
HbO.sub.2, which could be at least 1%. In a preferred situation
these increases could be higher and on the order of 10% or 20% and
up (5% and 10% for HbO.sub.2). In still another example, it might
be desired to decrease the pulmonary arterial blood pressure, the
systemic arterial blood pressure, the systemic systolic pressure or
the systemic diastolic pressure. These decreases could be at least
5% compared to their value before implantation. In a preferred
situation these decreases could be higher and on the order of 10%
or 20% and up. In yet another example, the blood flow rate could
increase from at least 5 ml/min compared to before implantation to
a situation where the shunt is capable of carrying up to 5000
ml/min of blood at e.g. a pressure differential across the shunt
device of 70 mmHg.
[0050] The description supra relates to a shunt device whereby the
blood flow rate could be changed and controlled. In these
situations, the structural parameters of the shunt device, such as
the length, cross section area and radius are fixed. However, in an
alternate embodiment, described infra, the shunt device could
change its cross section area, radius and/or length. This could be
accomplished either in a controlled fashion, like with a controller
and sensor(s) as described supra, or in a self-adjustable fashion
(i.e. self-organizing fashion).
[0051] FIG. 6 shows an example of a shunt device 610, 620 with a
mechanism of leaves 630 disposed in the lumen of the shunt device
that could change the cross section area of the lumen. Leaves 630
could be attached to a central axis or to the inner wall of shunt
device 610, 620 respectively. Two or more leaves could be used with
the capability of changing their position from a closed position
gradually to an open position (compare 610 and 612, and 620 and 622
respectively). The leaves in shunt devices 610, 620 could be
integrated with a controller 640 and/or sensor(s) 650 in a similar
fashion as described supra.
[0052] Leaves 630 could also be included as a self-adjusting
mechanism for opening and closing of the shunt device. When the
blood flow increases or blood pressure increases, the flexible
leaves automatically open up from a more or less closed position to
a more or less open position, and vice versa.
[0053] FIG. 7 shows an example of a shunt device 710 that is made
of a smart material such as a memory metal/alloy that can change
its length and cross sectional area (radius). For instance, shunt
device 710 could be made longer as shown by 720 or wider as shown
by 730 (larger cross sectional area). Shunt devices 710 could be
integrated with a controller 740 and/or sensor(s) 750 in a similar
fashion as described supra. Mechanisms of memory metals/alloys
(including particular stent-graft materials) and their controls are
known in the art.
[0054] In a self-adjustable fashion it could e.g. be desirable to
keep the blood flow rate at a level or range across the shunt
device without any controller; i.e. the shunt device is
self-organizing. To establish this the length and radius need to
work in tandem as a function of .DELTA.P and according to the
Poiseuille equation (see supra) (see FIG. 8). For instance, length
and .DELTA.P have a linear relationship such that when .DELTA.P
increases the length increases in a linear fashion to maintain the
blood flow rate at the same level, and vice versa. The radius and
.DELTA.P have an inverse non-linear relationship such that when
.DELTA.P increase the radius decreases in a non-linear fashion to
maintain the blood flow rate at the same level, and vice versa. It
is pointed out that the length and radius have to work in opposite
and unequal value to maintain a particular blood flow rate (see
supra for Poiseuille equation). Shunt device 810 should then be
made of a material that is capable of increasing its length, but
simultaneously decreasing its radius when .DELTA.P increases,
(indicated by changing from 810 and 820). Examples of such
materials are elastic materials with reinforced filaments or fibers
arranged and distributed over (or within) the shunt device (not
shown in 810, 820) to ensure selected and directional changes,
according to Poiseuille equation; i.e. (i) an increase in cross
sectional area with a decrease in length, and (ii) a decrease in
cross sectional area with an increase in length.
[0055] Other than following the Poiseuille equation one could
change the blood flow rate by following Ohm's law by increasing the
resistance to blood flow through the shunt device. Means to
increase this resistance could for instance be accomplished by
disposing roughness or obstacles such as bumps 930 or
filaments/spokes 940 to the inner wall of the lumen of shunt device
910, 920 respectively as shown in FIG. 9. The blood flow could then
also change from laminar flow to non-laminar flow.
[0056] FIGS. 10-12 show additional information regarding some
physiological effects of an aorto-caval fistula in rats. These
effects are the result of a study performed by the inventors of the
present invention. FIG. 10 shows the effect of an aorto-caval
fistula on several groups of experimental animals. In each group
the presence of an aorto-caval fistula was associated with
increased aortic blood flow (AF) and with increased partial
pressure of oxygen in arterial blood (PaO.sub.2) in rats that were
receiving supplemental oxygen (FiO.sub.2 =0.24, or the fraction of
inspired oxygen was 24%). Measurements of: (A): Aortic flow (24%
O2) and (B): Arterial blood oxygen tension (FiO.sub.2=0.24)
(PaO.sub.2). Note that groups PM and PFM received FiO.sub.2=0.50
during experimentation. Group N represents normal rats (n=6), Group
F underwent aorto-caval fistula (n=6), Group P underwent left
pneumonectomy (n=6), Group PF underwent left pneumonectomy and the
creation of an aorto-caval fistula (n=6), Group M received a toxin
that causes pulmonary hypertension called monocrotaline (n=6),
Group FM underwent aorto-caval fistula and received monocrotaline
(n=6), Group PM underwent left pneumonectomy and received
monocrotaline (n=6), Group PFM underwent left pneumonectomy and the
creation of an aorto-caval fistula and then received monocrotaline
(n=6). (**=p<0.01).
[0057] FIG. 11 shows the effect of the presence of an aorto-caval
fistula in several groups of experimental animals. Aorta-caval
fistuala attenuates the development of pulmonary arterial
hypertension. The measurements shown in FIG. 11 are of mean
pulmonary artery pressures (PAP). Group N represents normal rats
(n=6), Group F underwent aorto-caval fistula (n=6), Group P
underwent left pneumonectomy (n=6), Group PF underwent left
pneumonectomy and the creation of an aorto-caval fistula (n=6),
Group M received monocrotaline (n=6), Group FM underwent
aorto-caval fistula and received monocrotaline (n=6), Group PM
underwent left pneumonectomy and received monocrotaline (n=6),
Group PFM underwent left pneumonectomy and the creation of an
aorto-caval fistula and then received monocrotaline (n=6).
(*=p<0.05,**=p<0.01).
[0058] FIG. 12 shows photomicrographs of small pulmonary arteries
(A-D). (A) shows an example that normal rat (group N) arterioles do
not have evidence of neointimal formation (grade 0). (B) shows an
example of a grade 1 neointimal lesion (<50% occlusion) seen in
rats that received monocrotaline alone (group M). (C) shows an
example of grade 1 neointimal lesion (<50% occlusion) seen in
rats that underwent left pneumonectomy and the creation of an
aortocaval fistula (ACF) and then received monocrotaline (group
PMF). (D) shows an example of a grade 2 neointimal lesion (>50%
occlusion) seen in rats that underwent left pneumonectomy and
received monocrotaline (group PM). All photomicrographs (X400),
elastin van Gieson stain.
[0059] The present invention has now been described in accordance
with several exemplary embodiments, which are intended to be
illustrative in all aspects, rather than restrictive. Thus, the
present invention is capable of many variations in detailed
implementation, which may be derived from the description contained
herein by a person of ordinary skill in the art. For example, in
some instances, it may be possible and desirable to implant two or
more shunt devices at different locations between the arterial and
venous sides of the vasculature. In cases of such multiple shunt
device implantations, the individual shunts may be implanted in
close proximity to each other or may be distributed at different
regions of the vasculature.
[0060] In another aspect, it should be pointed out that the present
invention could be used as preventative care or as a therapy for a
condition or disease. Furthermore, as a person of average skill
would readily appreciate, the long-term implantable shunt device
could be beneficial to improve the performance in athletes,
military service personnel, performance animals (e.g. dogs and
horses).
[0061] The preferred location of the shunt device is between the
aorta and inferior vena cava as described supra. However, it would
be feasible to implant one or more shunt devices for a long-term
period in the pelvis area to link the common iliac artery and vein
or femoral artery and vein. In another embodiment the shunt device
could be positioned in the axilla and it would link the axillary
artery and vein. In yet another embodiment the device could be
positioned close to the clavicle and link the subclavian artery and
vein.
[0062] All such variations and other variations are considered to
be within the scope and spirit of the present invention as defined
by the following claims and their legal equivalents.
* * * * *