1. Field of the Invention
This application relates to cannulae and, in particular, to cannulae capable of enhancing blood flow around the cannulae within the vasculature of a patient.
2. Description of the Related Art
Treatment and diagnosis of a variety of health conditions in a patient can involve withdrawing blood from the patient's vascular system. For example, a syringe can be inserted into the patient's vasculature to withdraw blood for testing. It is sometimes necessary to introduce blood or other fluids into a patient's vasculature, e.g., an injection via an intravenous line, to provide treatment or obtain a diagnosis.
Treatment of organ failure can involve coordinated withdrawal and introduction of blood, in connection with some additional treatment. Dialysis, for example, involves withdrawing blood from the vasculature, filtering the blood, and infusing the blood back into the vasculature for further circulation. An emerging treatment for congestive heart failure involves coordinated withdrawal of blood from and infusion of blood into the vasculature without further treatment. Both such treatments sometimes call for the insertion of a cannula into the vasculature of the patient.
The size of the cannula employed in these and other vascular treatments can sometimes approach the size of the vessel into which it is inserted. For example, relatively large cannula size may be required where the treatment requires significant amounts of blood to be withdrawn at relatively high flow rates. The desirability of employing multilumen cannulae is another factor that contributes to increased cannula size. Depending on the application, larger cannulae can present a risk to tissue located downstream of where the cannulae are applied. For example, as the size of the cannula to be introduced approaches the size of the blood vessel, blood-flow downstream of the cannula may be restricted. Prolonged restriction of the vessel can lead to ischemia-related pathology.
Overcoming many if not all of the limitations of the prior art, the present invention, in one embodiment, provides a perfusion cannula system for directing blood through the vasculature of a patient. The cannula system includes a cannula body that comprises a proximal end, a distal end, and at least one lumen extending therebetween. The cannula system also includes a balloon and a means for deploying the balloon within the vasculature. The balloon is located on an exterior surface of the cannula body. The cannula system provides space between a vessel wall and the cannula body when the cannula body resides within the patient to permit blood flow past the cannula body.
In another embodiment, a perfusion cannula system for directing blood through the vasculature of a patient comprises means for creating space around the cannula body within the vasculature to permit blood flow past the cannula.
In another embodiment, a perfusion system for directing blood through the vasculature of a patient comprises a multilumen cannula. A plurality of radially spaced balloons are configured to be selectively inflated while residing with the vasculature to create space around the cannula within the vasculature to permit blood flow past the cannula.
In an additional embodiment, a perfusion cannula system comprises a cannula body having an aperture formed therein in fluid communication with a lumen. A sleeve is carried by the cannula and is configured to be moveable relative to the aperture to selectively cover and uncover the aperture as desired.
In another embodiment, a perfusion cannula system comprises means for enhancing blood flow past the cannula when the cannula body resides within the patient.
In another embodiment, an extracardiac heart assist system comprises a pump that has an inlet and an outlet. An inflow conduit is coupled with the inlet. An outflow conduit is coupled with the outlet. An intravascular conduit is configured to provide fluid communication between the vasculature of a patient and at least one of the inflow conduit and the outflow conduit. The intravascular conduit has a proximal end, a distal end, at least one lumen extending therebetween, and a means for selectively enhancing blood flow past the cannula when the cannula resides within the patient.
In another embodiment, a method of treating a patient using an extracardiac heart assist system comprises the steps of: inserting a cannula system into the vasculature of a patient, the cannula system being actuatable to enhance blood flow past the cannula when the cannula resides in the vasculature of the patient; and selectively actuating the cannula system, whereby blood flow past the cannula is enhanced.
These and other features and advantages of the invention will now be described with reference to the drawings, which are intended to illustrate and not to limit the invention.
Turning now to the drawings provided herein, more detailed descriptions of various embodiments of heart assist systems and cannulae for use therewith are provided below.
A variety of cannulae are described herein that can be used in connection with a variety of heart assist systems that supplement blood perfusion. Such systems preferably are extracardiac in nature. In other words, the systems supplement blood perfusion, without the need to interface directly with the heart and aorta. Thus, the systems can be applied without major invasive surgery. The systems also lessen the hemodynamic burden or workload on the heart by reducing afterload, impedence, and/or left ventricular end diastolic pressure and volume (preload). The systems also advantageously increase peripheral organ perfusion and provide improvement in neurohormonal status. As discussed more fully below, the systems can be applied using one or more cannulae, one or more vascular grafts, and a combination of one or more cannulae and one or more vascular grafts. For systems employing cannula(e), the cannula(e) can be applied through multiple percutaneous insertion sites (sometimes referred to herein as a multi-site application) or through a single percutaneous insertion site (sometimes referred to herein as a single-site application).
A. Heart Assist Systems and Methods Employing Multi-Site Application
With reference to
The heart assist system 10 comprises a pump 32, having an inlet 34 and an outlet 36 for connection of conduits thereto. The pump 32 preferably is a rotary pump, either an axial type or a centrifugal type, although other types of pumps may be used, whether commercially-available or customized. The pump 32 preferably is sufficiently small to be implanted subcutaneously and preferably extrathoracically, for example in the groin area of the patient 12, without the need for major invasive surgery. Because the heart assist system 10 is an extracardiac system, no valves are necessary. Any inadvertent backflow through the pump 32 and/or through the inflow conduit would not harm the patient 12.
Regardless of the style or nature chosen, the pump 32 is sized to generate blood flow at subcardiac volumetric rates, less than about 50% of the flow rate of an average healthy heart, although flow rates above that may be effective. Thus, the pump 32 is sized and configured to discharge blood at volumetric flow rates anywhere in the range of 0.1 to 3 liters per minute, depending upon the application desired and/or the degree of need for heart assist. For example, for a patient experiencing advanced congestive heart failure, it may be preferable to employ a pump that has an average subcardiac rate of 2.5 to 3 liters per minute. In other patients, particularly those with minimal levels of heart failure, it may be preferable to employ a pump that has an average subcardiac rate of 0.5 liters per minute or less. In yet other patients it may be preferable to employ a pump that is a pressure wave generator that uses pressure to augment the flow of blood generated by the heart.
In one embodiment, the pump 32 is a continuous flow pump, which superimposes continuous blood-flow on the pulsatile aortic blood-flow. In another embodiment, the pump 32 has the capability of synchronous actuation; i.e., it may be actuated in a pulsatile mode, either in copulsating or counterpulsating fashion.
For copulsating action, it is contemplated that the pump 32 would be actuated to discharge blood generally during systole, beginning actuation, for example, during isovolumic contraction before the aortic valve opens or as the aortic valve opens. The pump 32 would be static while the aortic valve is closed following systole, ceasing actuation, for example, when the aortic valve closes.
For counterpulsating actuation, it is contemplated that the pump 32 would be actuated generally during diastole, ceasing actuation, for example, before or during isovolumic contraction. Such an application would permit and/or enhance coronary blood perfusion. In this application, it is contemplated that the pump 32 would be static during the balance of systole after the aortic valve is opened, to lessen the burden against which the heart must pump. The aortic valve being open encompasses the periods of opening and closing, wherein blood is flowing therethrough.
It should be recognized that the designations copulsating and counterpulsating are general identifiers and are not limited to specific points in the patient's heart cycle when the pump 32 begins and discontinues actuation. Rather, they are intended to generally refer to pump actuation in which the pump 32 is actuating, at least in part, during systole and diastole, respectively. For example, it is contemplated that the pump 32 might be activated to be out of phase from true copulsating or counterpulsating actuation described herein, and still be synchronous, depending upon the specific needs of the patient or the desired outcome. One might shift actuation of the pump 32 to begin prior to or after isovolumic contraction or to begin before or after isovolumic relaxation.
Furthermore, the pulsatile pump may be actuated to pulsate asynchronously with the patient's heart. Typically, where the patient's heart is beating irregularly, there may be a desire to pulsate the pump 32 asynchronously so that the perfusion of blood by the heart assist system 10 is more regular and, thus, more effective at oxygenating the organs. Where the patient's heart beats regularly, but weakly, synchronous pulsation of the pump 32 may be preferred.
The pump 32 is driven by a motor 40 and/or other type of drive means and is controlled preferably by a programmable controller 42 that is capable of actuating the pump 32 in pulsatile fashion, where desired, and also of controlling the speed or output of the pump 32. For synchronous control, the patient's heart would preferably be monitored with an EKG in which feedback would be provided the controller 42. The controller 42 is preferably programmed by the use of external means. This may be accomplished, for example, using RF telemetry circuits of the type commonly used within implantable pacemakers and defibrillators. The controller may also be autoregulating to permit automatic regulation of the speed, and/or regulation of the synchronous or asynchronous pulsation of the pump 32, based upon feedback from ambient sensors monitoring parameters, such as pressure or the patient's EKG. It is also contemplated that a reverse-direction pump be utilized, if desired, in which the controller is capable of reversing the direction of either the drive means or the impellers of the pump. Such a pump might be used where it is desirable to have the option of reversing the direction of circulation between two blood vessels.
Power to the motor 40 and the controller 42 may be provided by a power source 44, such as a battery, that is preferably rechargeable by an external induction source (not shown), such as an RF induction coil that may be electromagnetically coupled to the battery to induce a charge therein. Alternative power sources are also possible, including a device that draws energy directly from the patient's body; e. g., the patient's muscles, chemicals or heat. The pump can be temporarily stopped during recharging with no appreciable life threatening effect, because the system only supplements the heart, rather than substituting for the heart.
While the controller 42 and power source 44 are preferably pre-assembled to the pump 32 and implanted therewith, it is also contemplated that the pump 32 and motor 40 be implanted at one location and the controller 42 and the power source 44 be implanted in a separate location. In one alternative arrangement, the pump 32 may be driven externally through a percutaneous drive line or cable, as shown in
The inlet 34 of the pump 32 is preferably connected to an inflow conduit 50 and an outflow conduit 52 to direct blood flow from one peripheral blood vessel to another. The conduits 50, 52 preferably are flexible conduits, as discussed more fully below. The conduits 50, 52 are coupled with the peripheral vessels in different ways in various embodiments of the heart assist system 10. As discussed more fully below, at least one of the conduits 50, 52 can be connected to a peripheral vessel, e.g., as a graft, using an anastomosis connection, and at least one of the conduits 50, 52 can be coupled with the same or another vessel via insertion of a cannula into the vasculature. Also, more than two conduits are used in some embodiments, as discussed below.
The inflow and outflow conduits 50, 52 may be formed from Dacron, Hemashield, Gortex, PVC, polyurethane, PTFE, ePTFE, nylon, or PEBAX materials, although other synthetic materials may be suitable. The inflow and outflow conduits 50, 52 may also comprise biologic materials or pseudobiological (hybrid) materials (e.g., biologic tissue supported on a synthetic scaffold). The inflow and outflow conduits 50, 52 are preferably configured to minimize kinks so blood flow is not meaningfully interrupted by normal movements of the patient or compressed easily from external forces. In some cases, the inflow and/or outflow conduits 50, 52 may come commercially already attached to the pump 32. Where it is desired to implant the pump 32 and the conduits 50, 52, it is preferable that the inner diameter of the conduits 50, 52 be less than 25 mm, although diameters slightly larger may be effective.
In one preferred application, the heart assist system 10 is applied in an arterial-arterial fashion; for example, as a femoral-axillary connection, as is shown in
Where the conduit 50 is at least partially extracorporeal, the inflow cannula 60 also may be inserted through a surgical opening (e.g., as shown in
In another embodiment, the inflow conduit 50 is connected to the first blood vessel via an end-to-side anastomosis, rather than via the inflow cannula 60. The inflow conduit 50 could also be coupled with the first blood vessel via a side-to-side anastomosis connection mid-stream of the conduit where the inflow conduit were connected at its second end to an additional blood vessel or at another location on the same blood vessel (neither shown). Further details of these arrangements and other related applications are described in U.S. application Ser. No. 10/289,467, filed Nov. 6, 2002, the entire contents of which is hereby incorporated by reference in its entirety and made a part of this specification.
In another embodiment, the outflow conduit 52 also is coupled with the second blood vessel via a cannula, as shown in
It is preferred that application of the heart assist system 10 to the peripheral or non-primary blood vessels be accomplished subcutaneously; e.g., at a shallow depth just below the skin or first muscle layer so as to avoid major invasive surgery. It is also preferred that the heart assist system 10 be applied extrathoracically to avoid the need to invade the patient's chest cavity. Where desired, the entire heart assist system 10 may be implanted within the patient 12, either extravascularly, e.g., as in
In the case of an extravascular application, the pump 32 may be implanted, for example, into the groin area, with the inflow conduit 50 fluidly connected subcutaneously to, for example, the femoral artery 26 proximate the pump 32. The outflow conduit would be tunneled subcutaneously through to, for example, the left subclavian artery 24. In an alternative arrangement, the pump 32 and associated drive and controller could be temporarily fastened to the exterior skin of the patient, with the inflow and outflow conduits 50, 52 connected percutaneously. In either case, the patient may be ambulatory without restriction of tethered lines.
While the heart assist system 10 and other heart assist systems described herein may be applied to create an arterial-arterial flow path, given the nature of the heart assist systems, i.e., supplementation of circulation to meet organ demand, a venous-arterial flow path may also be used. For example, with reference to
When venous blood is mixed with arterial blood either at the inlet of the pump or the outlet of the pump the ratio of venous blood to arterial blood should be controlled to maintain an arterial saturation of a minimum of 80% at the pump inlet or outlet. Arterial saturation can be measured and/or monitored by pulse oximetry, laser doppler, colorimetry or other methods used to monitor blood oxygen saturation. The venous blood flow into the system can then be controlled by regulating the amount of blood allowed to pass through the conduit from the venous-side connection.
The connections of any or all of the conduits of the system 110 to the blood vessels may be via an anastomosis connection or via a connector, as described below in connection with
It is contemplated that, where an anastomosis connection is not desired, a connector may be used to connect at least one of the inflow conduit and the outflow conduit to a peripheral blood vessel. With reference to
Other types of connectors having other configurations are contemplated that may avoid the need for an anastomosis connection or that permit connection of the conduit(s) to the blood vessel(s). For example, it is contemplated that an L-shaped connector be used if it is desired to withdraw blood more predominantly from one direction of a peripheral vessel or to direct blood more predominantly into a peripheral vessel. Referring to
One advantage of discrete connectors manifests in their application to patients with chronic CHF. A connector eliminates a need for an anastomosis connection between the conduits 250, 252 and the peripheral blood vessels where it is desired to remove and/or replace the system more than one time. The connectors could be applied to the first and second blood vessels semi-permanently, with an end cap applied to the divergence for later quick-connection of the present invention system to the patient. In this regard, a patient might experience the benefit of the heart assist systems described herein periodically, without having to reconnect and redisconnect the conduits 250, 252 from the blood vessels via an anastomosis procedure each time. Each time it is desired to implement any of the embodiments of the heart assist system, the end caps would be removed and a conduit attached to the connector(s) quickly.
In the preferred embodiment of the connector 268, the divergence 276 is oriented at an acute angle significantly less than 90 degrees from the axis of the T-shaped fitting 270, as shown in
With or without a connector, with blood flow directed proximally toward the aorta 16, the result may be concurrent flow down the descending aorta, which will result in the reduction of afterload, impedence, and/or reducing left ventricular end diastolic pressure and volume (preload). Thus, the heart assist systems described herein may be applied so to reduce the afterload on the patient's heart, permitting at least partial if not complete CHF recovery, while supplementing blood circulation. Concurrent flow depends upon the phase of operation of the pulsatile pump and the choice of second blood vessel to which the outflow conduit is connected.
A partial external application of the heart assist systems is contemplated where a patient with heart failure is suffering an acute decompensation episode; i.e., is not expected to last long, or in the earlier stages of heart failure (where the patient is in New York Heart Association Classification (NYHAC) functional classes II or III). With reference to
Similarly, the outflow conduit 352 has a first end 362 and a second end 364 wherein the second end 364 is connected to a second non-primary blood vessel (e.g., the left subclavian artery 24, as shown in
As shown in
An alternative variation of the embodiment of
Specific methods of applying this alternative embodiment may further comprise coupling the inflow conduit 352 upstream of the outflow conduit 350 (as shown in
It is contemplated that a means for minimizing the loss of thermal energy in the patient's blood be provided where any of the heart assist systems described herein are applied extracorporeally. Such means for minimizing the loss of thermal energy may comprise, for example, a heated bath through which the inflow and outflow conduits pass or, alternatively, thermal elements secured to the exterior of the inflow and outflow conduits. Referring to
If desired, the present inventive system may further comprise a reservoir that is either contained within or in fluid communication with the inflow conduit. This reservoir is preferably made of materials that are nonthrombogenic. Referring to
As explained above, one of the advantages of several embodiments of the heart assist system is that such systems permit the patient to be ambulatory. If desired, the systems may be designed portably so that it may be carried directly on the patient. Referring to
B. Heart Assist Systems and Methods Employing Single-Site Application
As discussed above, heart assist systems can be applied to a patient through a single cannulation site. Such single-site systems can be configured with a pump located outside the vasculature of a patient, e.g., as extravascular pumping systems, inside the vasculature of the patient, e.g., as intravascular systems, or a hybrid thereof, e.g., partially inside and partially outside the vasculature of the patient.
1. Single-Site Application of Extravascular Pumping Systems
In one embodiment, the multilumen cannula 460 includes a first lumen 466 and a second lumen 468. The first lumen 466 extends from a proximal end 470 of the multilumen cannula 460 to a first distal end 472. The second lumen 468 extends from the proximal end 470 to a second distal end 474. In the illustrated embodiment, the second end 458 of the inflow conduit 450 is connected to the first lumen 466 of the multilumen cannula 460 and the second end 464 of the outflow conduit 452 is connected to the second lumen 468 of the multilumen cannula 460.
Where there is a desire for the patient 12 to be ambulatory, the multilumen cannula 460 preferably is made of material sufficiently flexible and resilient to permit the patient 12 to be comfortably move about while the multilumen cannula 460 is indwelling in the patient's blood vessels without causing any vascular trauma.
The application shown in
The pump 432 draws blood from the patient's vascular system in the area near the distal end 472 and into the lumen 466. This blood is further drawn into the lumen of the conduit 450 and into the pump 432. The pump 432 then expels the blood into the lumen of the outflow conduit 452, which carries the blood into the lumen 468 of the multilumen cannula 460 and back into the patient's vascular system in the area near the distal end 474.
The vascular graft 550 has a first end 554 and a second end 556. The first end 554 is sized and configured to couple to a non-primary blood vessel 558 subcutaneously to permit application of the extracardiac pumping system 510 in a minimally-invasive procedure. In one application, the vascular graft conduit 550 is configured to couple to the blood vessel 558 via an anastomosis connection. The second end 556 of the vascular graft 550 is fluidly coupled to the pump 532 to conduct blood between the non-primary blood vessel 558 and the pump 532. In the embodiment shown, the second end 556 is directly connected to the pump 532, but, as discussed above in connection with other embodiments, intervening fluid conducting elements may be interposed between the second end 556 of the vascular graft 550 and the pump 532. Examples of arrangements of vascular graft conduits may be found in U.S. application Ser. No. 09/780,083, filed Feb. 9, 2001, entitled EXTRA-CORPOREAL VASCULAR CONDUIT, which is hereby incorporated by reference in its entirety and made a part of this specification.
The insertion site 560 is configured to receive the cannula 562 therethrough in a sealable manner in the illustrated embodiment. In another embodiment, the insertion site 560 is configured to receive the outflow conduit 552 directly. The cannula 562 includes a first end 564 sized and configured to be inserted through the insertion site 560, through the cannula 550, and through the non-primary blood vessel 558. The conduit 552 has a second end 566 fluidly coupled to the pump 532 to conduct blood between the pump 532 and the blood vessel 558.
The extracardiac pumping system 510 can be applied to a patient, as shown in
2. Single-Site Application of Intravascular Pumping Systems
The impeller blade(s) 616 of the pumping means 614 of this embodiment may be driven in one or a number of ways known to persons of ordinary skill in the art. In the embodiment shown in
Variations of the intravascular embodiment of
In one embodiment, the pumping means 644 also includes a conduit 652 in which the pump 646 is housed. The conduit 652 may be relatively short, as shown, or may extend well within the designated blood vessel or even into an adjoining or remote blood vessel at either the inlet end, the outlet end, or both. The intravascular extracardiac system 642 may further comprise an additional parallel-flow conduit, as discussed below in connection with the system of
The intrasvascular extracardiac system 642 may further comprise inflow and/or outflow conduits or cannulae (not shown) fluidly connected to the pumping means 644, e.g., to the inlet and outlet of pump 646. Any suitable conduit or cannula can be employed. For example, a cannula having a downstream blood flow enhancing portion, such as the any of the cannulae of
In another embodiment, an intrasvascular pumping means 644 may be positioned within one lumen of a multilumen catheter so that, for example, where the catheter is applied at the left femoral artery, a first lumen may extend into the aorta proximate the left subclavian and the pumping means may reside at any point within the first lumen, and the second lumen may extend much shorter just into the left femoral or left iliac. Such a system is described in greater detail in U.S. application Ser. No. 10/078,283, incorporated by reference herein above.
The intravascular extracardiac system described herein may be inserted into a patient's vasculature in any means known by one of ordinary skill or obvious variant thereof. In one method of use, such a system is temporarily housed within a catheter that is inserted percutaneously, or by surgical cutdown, into a non-primary blood vessel and advanced through to a desired location. The catheter preferably is then withdrawn away from the system so as not to interfere with operation of the system, but still permit the withdrawal of the system from the patient when desired. Further details of intravascular pumping systems may be found in U.S. patent application Ser. No. 10/686,040, filed Oct. 15, 2003, which is hereby incorporated by reference herein in its entirety.
C. Potential Enhancement of Systemic Arterial Blood Mixing
One of the advantages of the present invention is its potential to enhance mixing of systemic arterial blood, particularly in the aorta. Such enhanced mixing ensures the delivery of blood with higher oxygen-carrying capacity to organs supplied by arterial side branches off of the aorta. A method of enhancing mixing utilizing the present invention preferably includes taking steps to assess certain parameters of the patient and then to determine the minimum output of the pump that, when combined with the heart output, ensures turbulent flow in the aorta, thereby enhancing blood mixing.
Blood flow in the aortic arch during normal cardiac output may be characterized as turbulent in the end systolic phase. It is known that turbulence in a flow of fluid through pipes and vessels enhances the uniform distribution of particles within the fluid. It is believed that turbulence in the descending aorta enhances the homogeneity of blood cell distribution in the aorta. It is also known that laminar flow of viscous fluids leads to a higher concentration of particulate in the central portion of pipes and vessels through which the fluid flows. It is believed that, in low flow states such as that experienced during heart failure, there is reduced or inadequate mixing of blood cells leading to a lower concentration of nutrients at the branches of the aorta to peripheral organs and tissues. As a result, the blood flowing into branch arteries off of the aorta will likely have a lower hematocrit, especially that flowing into the renal arteries, the celiac trunk, the spinal arteries, and the superior and inferior mesenteric arteries. That is because these branches draw from the periphery of the aorta The net effect of this phenomenon is that the blood flowing into these branch arteries has a lower oxygen-carrying capacity, because oxygen-carrying capacity is directly proportional to both hematocrit and the fractional O2 saturation of hemoglobin. Under those circumstances, it is very possible that these organs will experience ischemia-related pathology.
The phenomenon of blood streaming in the aorta, and the resultant inadequate mixing of blood resulting in central lumenal concentration of blood cells, is believed to occur when the Reynolds number (NR) for the blood flow in the aorta is below 2300. To help ensure that adequate mixing of blood will occur in the aorta to prevent blood cells from concentrating in the center of the lumen, a method of applying the present invention to a patient may also include steps to adjust the output of the pump to attain turbulent flow within the descending aorta upstream of the organ branches; i.e., flow exhibiting a peak Reynolds number of at least 2300 within a complete cycle of systole and diastole. Because flow through a patient is pulsatile in nature, and not continuous, consideration must be given to how frequently the blood flow through the aorta has reached a certain desired velocity and, thus, a desired Reynolds number. The method contemplated herein, therefore, should also include the step of calculating the average Womersley number (NW), which is a function of the frequency of the patient's heart beat. It is desired that a peak Reynolds number of at least 2300 is attained when the corresponding Womersley number for the same blood flow is approximately 6 or above.
More specifically, the method may comprise calculating the Reynolds number for the blood flow in the descending aorta by determining the blood vessel diameter and both the velocity and viscosity of the fluid flowing through the aorta. The Reynolds number may be calculated pursuant to the following equation:
where: V=the velocity of the fluid; d=the diameter of the vessel; and υ=the viscosity of the fluid. The velocity of the blood flowing through the aorta is a function of the cross-sectional area of the aorta and the volume of flow therethrough, the latter of which is contributed both by the patient's own cardiac output and by the output of the pump of the present invention. Velocity may be calculated by the following equation:
where Q=the volume of blood flowing through the blood vessel per unit time, e. g., the aorta, and r=radius of the aorta. If the relationship between the pump output and the velocity is already known or independently determinable, the volume of blood flow Q may consist only of the patient's cardiac output, with the knowledge that that output will be supplemented by the subcardiac pump that is part of the present invention. If desired, however, the present system can be implemented and applied to the patient first, before calculating Q, which would consist of the combination of cardiac output and the pump output.
The Womersley number may be calculated as follows:
NW=r{square root}{square root over (2πω/)}υ
where r is the radius of the vessel being assessed, ω is the frequency of the patient's heartbeat, and υ=the viscosity of the fluid. For a peak Reynolds number of at least 2300, a Womersley number of at least 6 is preferred, although a value as low as 5 would be acceptable.
By determining (i) the viscosity of the patient's blood, which is normally about 3.0 mm2/sec sec (kinematic viscosity), (ii) the cardiac output of the patient, which of course varies depending upon the level of CHF and activity, and (iii) the diameter of the patient's descending aorta, which varies from patient to patient but is about 21 mm for an average adult, one can determine the flow rate Q that would result in a velocity through the aorta necessary to attain a Reynolds number of at least 2300 at its peak during the patient's heart cycle. Based upon that determination of Q, one may adjust the output of the pump of the present invention to attain the desired turbulent flow characteristic through the aorta, enhancing mixing of the blood therethrough.
One may use ultrasound (e.g., echocardiography or abdominal ultrasound) to measure the diameter of the aorta, which is relatively uniform in diameter from its root to the abdominal portion of the descending aorta. Furthermore, one may measure cardiac output using a thermodilution catheter or other techniques known to those of skill in the art. Finally, one may measure viscosity of the patient's blood by using known methods; for example, using a capillary viscosimeter. It is expected that in many cases, the application of this embodiment of the present method will provide a basis to more finely tune the system to more optimally operate the system to the patient's benefit. Other methods contemplated by the present invention may include steps to assess other patient parameters that enable a person of ordinary skill in the art to optimize the present system to ensure adequate mixing within the vascular system of the patient.
Alternative inventive methods that provide the benefits discussed herein include the steps of, prior to applying a shape change therapy, applying a blood supplementation system (such as one of the many examples described herein) to a patient, whereby the methods are designed to improve the ability to reduce the size and/or wall stress of the left ventricle, or both ventricles, thus reducing ventricular loading. Specifically, one example of such a method comprises the steps of providing a pump configured to pump blood at subcardiac rates, providing inflow and outflow conduits configured to fluidly communicate with-non-primary blood vessels, fluidly coupling the inflow conduit to a non-primary blood vessel, fluidly coupling the outflow conduit to the same or different (primary or non-primary) blood vessel and operating the subcardiac pump in a manner, as described herein, to reduce the load on the heart, wherein the fluidly coupling steps may comprise anastomosis, percutaneous cannulazation, positioning the distal end of one or both conduits within the desired terminal blood vessel or any combination thereof. The method further comprises, after sufficient reduction in ventricular loading, applying a shape change therapy in the form of, for example, a cardiac reshaping device, such as those referred to herein, or others serving the same or similar function, for the purpose of further reducing the size of and/or wall stress on one or more ventricles and, thus, the heart, and/or for the purpose of maintaining the patient's heart at a size sufficient to enhance recovery of the patient's heart.
With reference to
With reference to
The cannula 700 comprises a proximal end 708, a distal end 712, and at least one lumen that extends therebetween. With reference to
One or more apertures 726 may be formed in the cannula 700 proximate the distal end 712, although such apertures may also be formed proximate the distal end 724. The apertures 726 may be positioned close together or spaced circumferentially around the portion of the cannula 700 defining the lumen 716. The apertures 726 decrease the pressure drop across the distal end 712, thereby minimizing damage to vessel walls from jetting effects. Where one ore more apertures are formed proximate the distal end 724, the apertures decrease the pressure differential across the distal end 724, thereby minimizing the tendency of the vessel wall to be sucked into the distal end 724. Further tip arrangements that may be advantageously employed that provide desired outflow characteristics are described in more detail in U.S. patent application Ser. No. 10/706,346, filed Nov. 12, 2003, which is hereby expressly incorporated by reference herein in its entirety.
The lumens 716, 720 of the cannula 700 may be arranged in any of a number of different ways. For example, the two lumens may be joined in a side-by-side manner, forming a “figure-8” when viewed from the proximal end 708. In another embodiment, the cannula 700 may contain within it two or more side-by-side lumens. A cylindrical cannula body could be formed with a wall extending across the cylinder at a diameter to form two lumens. A cylindrical cannula body with concentrically positioned lumens is also contemplated.
The cannula system also includes an auxiliary lumen 728 that is in fluid communication with the balloon 704. The auxiliary lumen 728 may be defined in the body of the cannula 700. The lumen 728 preferably extends from the proximal end 708 of the cannula 700 to the balloon 704. The lumen 728 is referred to herein as an “auxiliary lumen” because it is generally substantially smaller than the lumens 716, 720 and because it enables a function that is not primary to the operation of the cannula 700. The lumen 728 is one means for deploying the balloon 704 within the vasculature and in one embodiment is an inflation lumen for the balloon 704. Preferably, the lumen 728 may be selectively fluidly coupled with a source of any suitable inflation media. The inflation media may be another means for deploying the balloon 704. The inflation media may include a suitable gas or liquid, such as saline. The inflation media may be delivered by way of a syringe (not shown), which is another means for deploying the balloon 704.
The balloon 704 is formed of an inflatable material that can be actuated from a deflated state to an inflated state. When in the deflated state, the balloon 704 preferably substantially conforms to at least a portion of the outside surface of the cannula 700. The balloon 704 is also one form of a collapsible element that can be selectively collapsed to ease insertion of the cannula system 700 into the vasculature. After being inserted into the patient, as described in more detail below, the balloon 704 may be inflated to the inflated state shown in
In one embodiment, the balloon 704 has a tubular configuration when in the inflated state. The tubular configuration of the balloon 704 provides an inside surface that defines a perfusion lumen 732. The perfusion lumen 732 is a generally longitudinally extending lumen, e.g., one that is generally parallel to the lumens 716, 720. As shown in
Additional features that may be incorporated into the cannula 700 include a tapered tip 736 at the first distal end 712 and/or a tapered tip 740 at the second distal end 724. The tapered tips 736, 740 may facilitate insertion and threading of the cannula 700 into the patient. The cannula 700 may also be provided with a radiopaque marker 744, which may be positioned proximate the distal end 712. The cannula 700 could further comprise markings 748 near the proximal end 708 and a known distance from one or more of the distal ends 712, 724. The markings 748, as well as the radiopaque marker 744, can be used to accurately position the cannula 700 when inserted within the patient.
With reference to
The balloons 804 are one form of an expandable element, e.g., one that may be selectively expanded to provide the function of passive perfusion, as discussed above. The balloon 804 is also one form of a collapsible element that is selectively collapsible to ease insertion of a cannula system into the vasculature. Other forms of collapsible and expandable elements are also possible, such as those that employ one or more mechanically actuatable elements and those that employ one or more elements that automatically collapse or expand, such as self-expanding elements.
The balloons 804 may be made of inflatable material, e.g., one capable of taking on an inflated and deflated state. In the deflated state, the balloons 804 would conform to at least a portion of the outside surface of the cannula 800. Once inserted within the patient, as described in more detail below, the balloons 804 would be inflated to the inflated state shown in
With reference to
In one embodiment the sleeve 972 is carried by the cannula 902 and is configured to be moveable relative to the apertures 968 to selectively cover and uncover the apertures 968 as desired. The sleeve 972 can be carried on either the outside or the inside of the cannula 902. For example, when the apertures 968 are formed on the body of the cannula 902 to provide fluid communication between the lumen 916 and the blood vessel, the sleeve 972 could be carried within the lumen 916. The sleeve 972 could be carried within the lumen 920 in a similar fashion to selectively cover and uncover apertures formed in the body of the cannula 902 to provide fluid communication between the lumen 920 and the blood vessel. In the illustrated embodiment, the sleeve 972 is on the outside of the body of the cannula 902. The sleeve 972 can be configured to move radially with respect to the cannula 902. The sleeve 972 can also be configured to move longitudinally, e.g., distally or proximally, with respect to the cannula 902.
The apertures 968 can be selectively uncovered while the cannula system 900 resides within a patient's body. Here, the sleeve 972 and apertures 968 are used primarily to selectively provide active perfusion of blood downstream of the location of the cannula 902 within the blood vessel. As used herein “active perfusion” is used in its ordinary sense and is a broad term that includes providing additional flow of blood under external blood pressure, e.g., the blood pressure generated by a pump forcing blood into the lumen 916, into the vessel to increase downstream flow of blood.
Any of the cannulae described herein may be made from various materials to improve their viability in long-term treatment applications. For example, it is preferred that the biocompatibility of the cannula be improved compared to uncoated cannulae to prevent adverse reactions such as compliment activation and the like. To prevent such side effects, the interior lumens of the cannulae can be coated with biocompatible materials. Also known in the art are anti-bacterial coatings. Such coatings may be very useful on the outer surface of the cannula. This is especially true at or about where the cannula enters the patient's skin. At such a location, the patient is vulnerable to introduction of bacteria into the body cavity. Anti-bacterial coatings can reduce the likelihood of infection and thus improve the viability of long-term treatments.
In one application, a cannula may be integrated into a heart assist system. The heart assist system may be configured in any number of ways. Various heart assist systems have been described above. In addition, as shown in to
Referring to
In operation, the pump draws blood from the patient's vascular system in the area near the distal end 724 and into the second lumen 720. The blood is further drawn into the lumen of the inflow conduit 780 and into the pump 784. The pump 784 then expels the blood into the lumen of the outflow conduit 776. The lumen of the outflow conduit 776 carries the blood into the second lumen 716 of the cannula 700 and back into the patient's vascular system in the area near the distal end 712.
According to one method of treating a patient using an extracardiac heart assist system, the cannula system is inserted into the vasculature of a patient and selectively actuated to enhance blood flow past the cannula. As described in greater detail below, with reference to embodiments illustrated in
Referring to
Referring to
Referring to
Although the foregoing invention has been described in terms of certain preferred embodiments, other embodiments will be apparent to those of ordinary skill in the art. Additionally, other combinations, omissions, substitutions and modification will be apparent to the skilled artisan, in view of the disclosure herein. Accordingly, the present invention is not intended to be limited by the recitation of the preferred embodiments, but is instead to be defined by reference to the appended claims.