Blood flow measurement system

Abstract

To provide a blood flow rate measurement system that measures a fluid flow rate in a blood vessel having a catheter-based heart pump inserted therein, without relying on measurement of electric current drawn out by a motor that drives the heart pump.SOLUTION: A turbine (200) is disposed at or near a distal end of a heart pump catheter (202). Blood or other fluid flowing through the blood vessel urges blades (204) of the turbine (200) to rotate. The turbine (200) is mechanically coupled to a signal generator, which generates a signal indicative of a rotational speed of the turbine (200), where the rotational speed of the turbine (200) is dependent at least in part on a speed of the fluid flowing through the blood vessel. A blood tachometer external to the body of the patient calculates the blood flow rate from the rotational speed of the turbine (200). In some cases, the blades (204) are collapsible to reduce diameter of the turbine (200), thereby facilitating insertion of the system into the blood vessel.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of U.S. Patent Application No. 16 / 353,132, entitled "Blood Flow Rate Measurement System," filed March 14, 2019, the entire contents of which are incorporated herein by reference for all purposes.

[0002] Technical Field The present invention relates to blood flow measurement systems, and more particularly to catheter-mounted, turbine-driven blood flow measurement systems. [Background technology]

[0003] Related Technology Many patients with coronary artery disease (CAD) would benefit from stent percutaneous coronary intervention (CPI) or coronary artery bypass graft surgery. However, some of these patients are considered to be at too high risk for complications that may arise during these procedures. Risk factors include older age; history of disease such as kidney disease, stroke, or diabetes; location of CAD, such as left main or two-vessel disease; difficult plaque type, such as calcified or long lesions; chronic total occlusion of a coronary artery; previous open-heart surgery; and advanced heart failure.

[0004] Interventional cardiologists treat some of these high-risk patients with an advanced catheter procedure called percutaneous coronary intervention (CHIP) for complete or complex high-risk cases. However, high-risk CAD patients who have also been diagnosed with advanced heart failure or severe valvular heart disease are particularly vulnerable during a CHIP procedure because their weakened heart muscle compromises blood pressure and cannot efficiently pump blood throughout the body.

[0005] For high-risk CAD patients, a ventricular assist device may be used during CHIP to provide temporary support to the patient's heart by assisting in the circulation of blood through the patient's cardiovascular system. For example, a catheter with a heart pump on one end may be inserted by standard catheterization techniques through the femoral artery, into the ascending aorta, across the aortic valve, and into the left ventricle. Once in place, the heart pump assists the movement of blood from the left ventricle, through an inlet port near the tip and a cannula, to an outlet port, and into the ascending aorta.

[0006] Temporarily supporting the heart with a ventricular assist device during CHIP, such as for less than about 6 hours, is referred to as protected PCI. Exemplary ventricular assist devices include the Impella 2.5® and Impella CP® heart pumps available from Abiomed, Inc., Danvers, Mass. The Impella 2.5 heart pump has a catheter diameter of only 9 Fr and a pump motor diameter of only 12 Fr (versus 14 Fr for the Impella CP heart pump), although smaller catheter and motor diameters are highly desirable. Summary of the Invention

[0007] Overview of Aspects In one aspect of the present invention, a blood flow measurement system is provided. The system includes a catheter, a turbine, a signal generator, and a signal lead. The catheter has a length. The catheter is configured to be inserted into a blood vessel of a living organism, such as a human. The turbine is disposed near a distal end of the catheter.

[0008] The turbine includes at least one blade. The at least one blade is configured to rotate. The at least one blade is configured to rotate relative to the catheter. The at least one blade is configured to rotate in response to fluid flow through a blood vessel. The at least one blade is configured to rotate at a rotational speed that is at least partially dependent on a rate of fluid flow through a blood vessel.

[0009] A signal generator is mechanically coupled to the turbine. The signal generator is configured to generate a signal indicative of a rotational speed of the at least one blade. A signal lead is configured to carry a signal indicative of a rotational speed of the at least one blade. The signal lead is connected to the signal generator. The signal lead extends along the catheter.

[0010] In any embodiment, the signal generator may include a generator.

[0011] In any embodiment, the signal generator may include a magnet.

[0012] In any embodiment in which the signal generator includes a magnet, the blood flow measurement system may also include a coil. The magnet may be configured to rotate relative to the coil in response to rotation of the at least one blade.

[0013] In any embodiment in which the signal generator includes a magnet, the blood flow measurement system may also include a Hall effect sensor. The magnet may be configured to rotate relative to the Hall effect sensor in response to rotation of the at least one blade.

[0014] In any embodiment, the signal leads may include first and second conductive leads and / or optical fibers.

[0015] In any embodiment, a blood flow velocity meter may be included, which may be coupled to the signal lead, and which may be configured to measure a rate of fluid flow through a blood vessel based on a signal indicative of a rotational speed of the at least one blade.

[0016] In any embodiment, the at least one blade may be radially foldable.

[0017] In any embodiment, the signal lead may be configured to extend along the catheter to a location outside the living organism.

[0018] In any embodiment, a duct configured to direct at least a portion of fluid flow through a blood vessel toward the at least one blade may be included, and the at least one blade may be configured to rotate relative to the catheter at a rotational speed that depends at least in part on the shape and size of the duct.

[0019] In any embodiment having a duct, the duct may be radially collapsible.

[0020] In any embodiment having a duct, the duct may be tapered. [Brief description of the drawings]

[0021] The present invention will be better understood by reference to the following detailed description of illustrative embodiments taken in conjunction with the accompanying drawings, in which:

[0022] [Figure 1] 1 illustrates a percutaneous left heart pump inserted into a patient's blood vessel according to the prior art; [Diagram 2] FIG. 1 is an isometric view of the distal end of a heart pump catheter with a turbine and optional duct located at the end of the catheter to measure blood flow, according to one embodiment of the present invention. [Diagram 3]FIG. 13 is an isometric view of the distal end of a heart pump catheter with a turbine located near the end of the catheter to measure blood flow, according to another aspect of the present invention. [Figure 4] FIG. 4 is a schematic diagram of a signal generator mechanically coupled to the turbine of FIG. 2 or FIG. 3 according to one embodiment of the present invention. [Diagram 5] FIG. 5 is a detailed schematic diagram of the signal generator of FIG. 4 according to one embodiment of the present invention. [Figure 6] FIG. 5 is a detailed schematic diagram of the signal generator of FIG. 4 according to another embodiment of the present invention. [Figure 7] FIG. 5 is a detailed schematic diagram of the signal generator of FIG. 4 according to a third embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS Aspects of the invention provide an apparatus and method for measuring blood flow, such as total blood flow including natural heart action plus heart pump action, in a patient's blood vessel when the catheter-based heart pump is inserted into the vessel without relying on measuring the current drawn by the motor driving the heart pump. Aspects of the invention include a turbine disposed at or near the distal end of the heart pump catheter. Rotation of the turbine blades is induced by blood or other fluid flowing through the vessel. The turbine is mechanically coupled to a signal generator that generates a signal indicative of the rotational speed of the turbine; the rotational speed of the turbine is at least partially dependent on the velocity of the fluid flowing through the vessel. The signal is conveyed by a lead to the proximal end of the catheter outside the patient's body where a blood flow velocimetry device calculates blood flow from the rotational speed of the turbine. Advantageously, the lead is small in diameter.

[0024] definition As used herein, the following terms have the following definitions unless otherwise stated.

[0025] A turbine is a rotating mechanical device that extracts energy from a flowing fluid and converts it into useful work. When combined with a generator, the work produced by a turbine can be used to generate electricity. A turbine is a turbomachine with at least one moving part called a rotor assembly, which includes a shaft or drum on which blades are attached. The moving fluid acts on the blades, which move them and impart rotational energy to the rotor (Wikipedia, turbine). Turbines as used herein include, but are not limited to, Pelton turbines, Francis turbines, and Kaplan turbines.

[0026] Reduction in diameter of prior art heart pumps FIG. 1 shows an exemplary prior art heart pump 100 including an elongated catheter 102 whose distal portion 104 is inserted through a patient's blood vessel 106 into a heart 108. A proximal end 110 of the catheter 102 is connected to an external control unit 112, such as an Automated Impella® Controller available from Abiomed, Inc., Danvers, Mass. Conventional heart pumps, such as the Impella 2.5® and Impella CP®, include an electric motor that drives impeller blades. Blood is drawn through an inlet port 114 and expelled through an outlet port 116. Pumped blood is indicated by arrows 118, 120, and 122. The speed of the motor 124, and therefore the speed of the pump 100 and the amount of blood pumped, can be automatically ascertained by the control unit 112 by measuring the current drawn by the motor 124. However, as mentioned above, the motor 124 is relatively large in diameter.

[0027] By relocating the motor 124 from the distal portion 104 of the catheter 102 to a location outside the patient's body and driving the impeller blades with a flexible drive shaft (not shown) that extends through the catheter 102, the diameter of the heart pump 100 is reduced. However, such a long flexible drive shaft experiences significant friction and other losses along its length. Thus, the current drawn by the external motor is not a reliable indicator of the rotational speed of the impeller blades or of the amount of blood pumped by the heart pump.

[0028] Turbine-type blood flow measurement system To overcome this problem and to provide a reliable measurement of fluid flow rate through a blood vessel, one embodiment of the present invention includes a turbine 200 at or near the distal end of a catheter 202 that also contains a heart pump (not shown), as illustrated in Figures 2 and 3.

[0029] One or more blades 204 of the turbine 200 rotate about an axis 206 driven by a fluid, such as blood, flowing past the turbine 200 and impinging on the blades 204. The axis 206 may, but need not, be aligned with a longitudinal axis 208 of the catheter 202. Optionally, a duct 210 (shown in phantom) may be included to protect the vessel wall during insertion and removal of the turbine 200 and to prevent the blades 204 from engaging the vessel wall and impeding the rotation of the blades 204 once the turbine 200 is in position. Optionally, the duct 210 may be tapered to increase the flow rate of the fluid flow 212 through the turbine 200. The duct 210 may be attached to the catheter 200 by, for example, a rigid or foldable fin, represented by fin 214. For clarity, the optional duct 210 is omitted from FIG. 3.

[0030] As shown diagrammatically in Figure 4, the turbine 200 drives a signal generator 400. The signal generator 400 generates a signal 404 indicative of the rotational speed of the turbine blades 204. The blades 204 are configured to rotate relative to the catheter 202 (Figure 2) at a rotational speed that depends at least in part on the velocity of the fluid 402 flowing through the blood vessel and the configuration of the duct 210 (if present), such as the taper of the duct 210.

[0031] The signal generator 400 is configured to generate a signal 404 indicative of the rotational speed of the blades 204. A signal lead 406, exemplified by two wires 408 and 410, is configured to carry the signal 404 to a blood flow velocimetry meter 412. The blood flow velocimetry meter 412 is configured to measure the rate of flow of the fluid 402 through the blood vessel based on the signal 404. In one embodiment, the blood flow velocimetry meter 412 calculates the flow rate by multiplying the rotational speed of the blades 204 by a coefficient. The coefficient may represent a linear or non-linear relationship between the rotational speed of the blades 204 and the flow rate of the fluid 402. This relationship may be determined empirically or by modeling the blades 204, the fluid 402, the vessel geometry, friction, etc.

[0032] In one embodiment, as shown diagrammatically in FIG. 5, the signal 404 indicative of the rotational speed of the turbine blades 204 is an AC signal whose frequency is proportional to the rotational speed of the blades 204 (not shown in FIG. 5 for clarity). In one such embodiment, the blades 204 are mechanically coupled to a magnet 500, so that the magnet 500 rotates with the blades 204, as indicated by arrow 502. A coil 504 is disposed in close proximity to the magnet 500. Each rotation of the magnet 500 induces a pulse of the signal 404 (one cycle 506 of a sine wave in this embodiment). The blood flow velocimetry meter 412 may count the pulses (cycles) received during a predefined time interval to measure the frequency of the signal 404. The coil 504 is shown with a core, although any suitable core, such as an iron core or an air core, may be used. Additionally, although the coil 504 is shown divided into two sections, the coil need not be divided.

[0033] Alternatively, the hemovelocity meter 404 may measure the voltage of the signal 404 , which is proportional to the rotational speed of the turbine blades 204 .

[0034] In another embodiment, illustrated diagrammatically in Figure 6, the coil 504 (Figure 5) is replaced by a Hall effect sensor 600. The output signal from the Hall effect sensor 600 may be processed (if necessary) by a threshold detector 602 to generate a signal 404 indicative of the rotational speed of the turbine blades 204 (not shown in Figure 6 for clarity). In this embodiment, the signal 404 consists of rectangular pulses 604. As with the first embodiment described with respect to Figure 5, the frequency of the pulses 604 is proportional to the rotational speed of the blades 204.

[0035] In yet another embodiment, illustrated diagrammatically in Figure 7, the leads 408 and 410 from the coil 504 described with respect to Figure 5 are connected to a light emitting diode (LED) 700. The LED 700 is optically coupled to the distal end of an optical fiber 702. Each pulse (cycle) of the signal from the coil 504 causes the LED to flash, thereby sending a light pulse along the optical fiber 702. This series of light pulses collectively form a signal 404 indicative of the rotational speed of the blade 204. Thus, in this embodiment, the optical fiber 702 is a lead 406 configured to carry the signal 404 to a blood flow velocimetry meter 412, which includes a light sensor (not shown) for detecting the light pulses.

[0036] In either embodiment, the leads 406 configured to carry the signal 404 may be discrete and may extend along the lumen of the catheter 202. Alternatively, the leads 406 may be integral to the catheter 202. For example, in some embodiments, the wires 408 and 410 are printed on the exterior and / or interior surface of the catheter 202 or embedded within the wall of the catheter 202. Similarly, in one embodiment, the optical fiber 702 is embedded within the wall of the catheter 202.

[0037] Although an embodiment with one magnet per turbine has been described, each turbine may include more than one magnet, in which case signal 404 may include more than one pulse per revolution of blade 204.

[0038] Although the heart pump pumps blood, the action of the patient's heart also pumps some blood. The total amount of blood flowing through the blood vessels is important to the health of the patient. "Upstream" means in the opposite direction to the direction of blood or other fluid flow, and "downstream" means in the same direction as the flow of blood or other fluid. Advantageously, if the turbine is located a distance upstream from the inlet port 114 (FIG. 1) of the heart pump or a distance downstream from the outlet port 116 of the heart pump, the aspects of the blood flow measurement system described herein measure the total fluid flow in the vessels, not just the amount of blood pumped by the heart pump. However, if the turbine is located between the inlet port 114 of the heart pump and the outlet port 116 of the heart pump, the blood flow measurement system measures the blood flow caused by the action of the heart plus the additional blood flow around the heart pump caused by jet pumping driven by blood ejected from the outlet port 116 of the heart pump.

[0039] Foldable turbine blades In some embodiments, the blades 204 are foldable in the radial direction, i.e., toward the axis 206. In some such embodiments, the blades 204 are made of a flexible material that can fold, contract, or compress to reduce the outer diameter 216 (FIG. 2) of the blades 204, at least while the catheter is inserted into the blood vessel. In some embodiments, the blades 204 are resilient. In some embodiments, the blades 204 are made of a shape-memory material that returns to a memory shape when warmed to a temperature equal to or slightly lower than the temperature of blood circulating in the human body. In some embodiments, each blade 204 includes multiple struts that fold or expand depending on the mode of the blade 204 (folded mode or extended mode). As a result, once the catheter is in position, the blades 204 open or otherwise return to an efficient shape to be driven by the fluid flowing through the blood vessel.

[0040] Any suitable structure and / or method may be used to initially compact the blades 204, extend the blades 204 once the turbine 200 is in place, and then fold the blades 204 in preparation for removing the turbine 200. Exemplary structures and methods are described in U.S. Pat. Nos. 9,611,743, 9,416,783, 8,944,748, 9,416,791, 9,314,558, 9,339,596, 9,067,006, 9,642,984, 8,932,141, 8,814,933, 8,814,933, and 9,750,860, and U.S. Patent Publication Nos. 2018 / 0080326, 2014 / 0039465, and 2018 / 0296742, the entire contents of each of which are incorporated herein by reference for all purposes. Some of the structures and / or methods described in the aforementioned documents include wires or drive shafts to advance, retract, and / or rotate components to extend or compress the impeller blades and / or pump. The same wires or drive shafts may be used in a similar manner to actuate structures configured to extend and / or compress the blades 204 of the turbine 200. Optionally or alternatively, different or additional wires or drive shafts may be used to actuate structures configured to extend and / or compress the blades 204 of the turbine 200. Optionally or alternatively, the reed 406, or a portion of the reed 406, may be used to actuate structures configured to extend and / or compress the blades 204 of the turbine 200.

[0041] The present invention is described through the above exemplary embodiments, but modifications and variations to the illustrated embodiments are possible without departing from the inventive concept disclosed herein. For example, specific parameter values ​​such as dimensions and materials may be stated in the context of the disclosed embodiments, but within the scope of the present invention, the values ​​of all parameters may vary over a wide range to suit different applications. Unless otherwise indicated in the context or understood by those skilled in the art, terms such as "about" mean within ±20%.

[0042] In this specification and in the claims, the term "and / or" when used in connection with a list of items means one or more of the items in the list, i.e., at least one of the items in the list, but not necessarily every item in the list. In this specification and in the claims, the term "or" when used in connection with a list of items means one or more of the items in the list, i.e., at least one of the items in the list, but not necessarily every item in the list. "Or" does not mean exclusive or.

[0043] Although aspects of the embodiments may be described with reference to flowcharts and / or block diagrams, the functions, operations, decisions, etc. of all or a portion of each block or combination of blocks may be combined, separated into separate operations, or performed in other orders. References to "modules" are for convenience and are not intended to limit the embodiment. All or a portion of each block, module, or combination thereof may be implemented as computer program instructions (e.g., software), hardware (e.g., combinatorial logic, application specific integrated circuit (ASIC), field programmable gate array (FPGA), processor, or other hardware), firmware, or a combination thereof.

[0044] The blood flow velocimetry device, the heart pump control unit, or portions thereof, may be implemented by one or more processors that execute or are controlled by instructions stored in a memory. Each processor may be a general-purpose processor, such as a central processing unit (CPU), a graphics processing unit (GPU), a digital signal processor (DSP), a special-purpose processor, or a combination thereof, as appropriate. However, when programmed with these instructions, the combination of the processor and memory collectively forms a special-purpose processor.

[0045] The memory may be a random access memory (RAM), a read only memory (ROM), a flash memory, or any other memory, or combination thereof, suitable for storing control software or other instructions and data. The instructions that define the functionality of the present invention may be delivered to the processor in many forms, including, but not limited to, information permanently stored on a non-transitory, non-writable tangible storage medium (e.g., a read only memory device within the computer, such as a ROM, or a device readable by the computer's I / O accessories, such as a CD-ROM or DVD disk), information alterably stored on a non-transitory, writable tangible storage medium (e.g., a floppy disk, a removable flash memory, and a hard drive), or information communicated to the computer over a communication medium, including a wired or wireless computer network. Additionally, although aspects may be described in conjunction with various example data structures, the system may be embodied using a variety of data structures.

[0046] The aspects of the present disclosure, or portions thereof, may be combined in ways not recited above and / or not expressly claimed. In addition, the embodiments disclosed herein may be suitably practiced in the absence of any element not specifically disclosed herein. Thus, the present invention should not be viewed as being limited to the disclosed embodiments.

[0047] Numerical terms such as "first," "second," and "third," used herein, for example, to distinguish respective wires 408 and 410 from one another, are not intended to indicate a particular order or total number of items in any particular embodiment. Thus, for example, a given embodiment may include only a second wire and a third wire.

Claims

1. at least one impeller blade configured to be driven by a motor (124), the rotation of the at least one impeller blade drawing blood into one or more inlet ports (114) of the heart pump (100) and expelling blood through one or more outlet ports (116) of the heart pump (100); a turbine (200) comprising at least one turbine blade (204) adjacent the at least one impeller blade, the at least one turbine blade (204) configured to rotate in response to fluid flow through the blood vessel (106) at a rotational speed that is at least partially dependent on the rate of fluid flow through the blood vessel (106); a signal generator (400) mechanically coupled to the turbine (200) and configured to generate a signal (404) indicative of a rotational speed of the at least one turbine blade (204); A system comprising:

2. The system of claim 1 , wherein the signal generator (400) comprises a generator.

3. The system of claim 1 , wherein the signal generator comprises a magnet (500).

4. The system of claim 3, further comprising a coil (504), the magnet (500) configured to rotate relative to the coil (504) in response to rotation of the at least one turbine blade (204).

5. The system of claim 3, further comprising a Hall effect sensor (600), the magnet (500) configured to rotate relative to the Hall effect sensor (600) in response to rotation of the at least one turbine blade (204).

6. The system of claim 1 , wherein the at least one turbine blade (204) is radially foldable.

7. 2. The system of claim 1, further comprising a duct (210) configured to direct at least a portion of a fluid flow through a blood vessel toward the at least one turbine blade (204); and the at least one turbine blade (204) configured to rotate relative to the catheter (202) at a rotational speed that is at least in part dependent on the shape and size of the duct (210).

8. The system of claim 7 , wherein the duct (210) is radially collapsible.

9. The system of claim 7 , wherein the duct (210) is tapered.

10. 8. The system of claim 7, wherein the duct is configured to be attached to the catheter (102, 202) by one or more fins (214).

11. The system of claim 1 , further comprising a motor (124), the motor (124) disposed at a location external to the patient.

12. The system of claim 11, wherein the motor (124) is configured to drive at least one impeller blade with a flexible drive shaft extending through the catheter (102, 202).

13. The system of any preceding claim, wherein the turbine (200) is positioned an upstream distance from the one or more inlet ports (114).

14. The system of any preceding claim, wherein the turbine (200) is positioned a downstream distance from the one or more outlet ports (116).

15. The system of any preceding claim, wherein the turbine (200) is disposed between the one or more inlet ports (114) and the one or more outlet ports (116).

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