Patent Description:
The present invention relates to blood flow measurement systems and, more particularly, to catheter-mounted, turbine-driven blood flow measurement systems.

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 too high-risk for complications that may occur during these procedures. Risk factors include: advanced age; history of disease, such as kidney disease, stroke or diabetes; location of the CAD, including left main or bifurcated disease; challenging plaque types, including calcified or long lesions; chronic total occlusion of the coronary arteries; previous open-heart surgery; and advanced heart failure.

Interventional cardiologists treat some of these high-risk patients with an advanced catheter-based procedure, referred to as complete or complex higher risk indicated percutaneous coronary intervention (CHIP). However, high-risk CAD patients that have also been diagnosed with advanced heart failure or severe heart valve disease are particularly vulnerable during CHIP procedures, due to weakened heart muscle, which compromises blood pressure and cannot pump blood efficiently to the body.

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

Temporarily, such as for less than about six hours, supporting the heart with a ventricular assist device during CHIP is referred to as protected PCI. Exemplary ventricular assist devices include Impella <NUM>® and Impella CP® heart pumps available from Abiomed, Inc. , Danvers, MA. Although the Impella <NUM> heart pump has a catheter diameter of only <NUM> Fr, and a pump motor diameter of only <NUM> Fr (<NUM> Fr for the Impella CP heart pump), smaller diameter catheters and motor diameters are highly desirable. Further prior art can be found in <CIT>.

According to the invention, a blood pump system comprising the features of claim <NUM> is provided. An example of the present disclosure provides a blood flow rate measurement system. 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 being, such as a human being. The turbine is disposed proximate a distal end of the catheter.

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 the blood vessel. The at least one blade is configured to rotate at a rotational speed that depends at least in part on speed of the fluid flow through the blood vessel.

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

In any embodiment, the signal generator may include an electrical generator.

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

In any embodiment in which the signal generator includes a magnet, the blood flow rate 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.

In any embodiment in which the signal generator includes a magnet, the blood flow rate 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.

In any embodiment, the signal lead may include first and second electrically conductive leads and/or an optical fiber.

Any embodiment may include a tachometer. The tachometer may be coupled to the signal lead. The tachometer may be configured to measure the speed of the fluid flow through the blood vessel, based on the signal indicative of the rotational speed of the at least one blade.

In any embodiment, the at least one blade may be radially collapsible.

In any embodiment, the signal lead may be configured to extend along the catheter to a location outside the living being.

Any embodiment may also include a duct configured to direct at least a portion of the fluid flow through the blood vessel toward the at least one blade. The at least one blade may be configured to rotate, relative to the catheter, at a rotational speed dependent at least in part on shape and size of the duct.

In any embodiment having the duct, the duct may be radially collapsible.

In any embodiment having the duct, the duct may be tapered.

The invention will be more fully understood by referring to the following Detailed Description of Specific Embodiments in conjunction with the Drawings, of which:.

Embodiments of the present disclosure provide apparatus and methods for measuring blood flow, such as total blood flow due to natural heart action plus heart pump action, in a blood vessel of a patient when a catheter-based heart pump is inserted into the blood vessel, without relying on measurements of electric current drawn by a motor that drives the heart pump. The present invention includes a turbine disposed at or near a distal end of the heart pump catheter. Rotation of the turbine blades is induced by blood or other fluid flowing through the blood vessel. The turbine is mechanically coupled to a signal generator, which generates a signal indicative of rotational speed of the turbine, which is dependent, at least in part, on speed of the fluid flowing through the blood vessel. The signal is carried by a lead to a proximal end of the catheter, external to the patient's body, where a tachometer calculates the blood flow rate from the rotational speed of the turbine. Advantageously, the lead is small in diameter.

As used herein, the following terms shall have the following definitions, unless otherwise indicated:
A turbine is a rotary mechanical device that extracts energy from a fluid flow and converts the energy into useful work. The work produced by a turbine can be used for generating electrical power when combined with a generator. A turbine is a turbomachine with at least one moving part called a rotor assembly, which includes a shaft or drum with blades attached. Moving fluid acts on the blades so that they move and impart rotational energy to the rotor. (Wikipedia, turbine. ) As used herein, turbines include, without limitation, Pelton, Francis and Kaplan turbines.

<FIG> shows an exemplary prior art heart pump <NUM> that includes an elongated catheter <NUM>, a distal portion <NUM> of which is inserted through a blood vessel <NUM> into a heart <NUM> of a patient. A proximal end <NUM> of the catheter <NUM> is connected to an external control unit <NUM>, such as an Automated Impella® Controller, available from Abiomed, Inc. , Danvers, MA. Conventional heart pumps, such as the Impella <NUM>® and Impella CP® heart pumps, include electric motors that drive impeller blades. Blood is drawn in through inlet ports <NUM> and expelled through outlet ports <NUM>. Pumped blood flow is indicated by arrows <NUM>, <NUM> and <NUM>. Speed of a motor <NUM>, and therefore speed of the pump <NUM> and amount of blood pumped, can be automatically ascertained by the control unit <NUM> by measuring electrical current drawn by the motor <NUM>. However, as noted, the motor <NUM> is relatively large in diameter.

Relocating the motor <NUM> from the distal portion <NUM> of the catheter <NUM> to a location outside the patient's body, and driving the impeller blades with a flexible drive shaft (not shown) extending through the catheter <NUM>, reduces the diameter of the heart pump <NUM>. However, such a long, flexible drive shaft is subject to significant friction and other losses along its length. Therefore, the current drawn by an 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.

To overcome this problem, and to provide reliable measurements of flow rate of a fluid through a blood vessel, an embodiment of the present invention includes a turbine <NUM> at or near the distal end of a catheter <NUM> that also includes a heart pump (not shown), as illustrated in <FIG> and <FIG>.

One or more blades <NUM> of the turbine <NUM> are driven to rotate, about an axis <NUM>, by fluid, such as blood, flowing past the turbine <NUM> and impinging on the blades <NUM>. The axis <NUM> may, but need not necessarily, align with a longitudinal axis <NUM> of the catheter <NUM>. Optionally, a duct <NUM> (shown in phantom) may be included to protect the walls of the blood vessel during insertion and removal of the turbine <NUM>, and to prevent the blades <NUM> engaging the walls, thereby preventing rotation of the blades <NUM>, once the turbine <NUM> is in position. Optionally, the duct <NUM> may be tapered to increase rate of fluid flow <NUM> through the turbine <NUM>. The duct <NUM> may, for example, be attached to the catheter <NUM> by rigid or collapsible fins, represented by fin <NUM>. The optional duct <NUM> is omitted from <FIG> for clarity.

The turbine <NUM> drives a signal generator <NUM>, as shown schematically in <FIG>. The signal generator <NUM> generates a signal <NUM> that is indicative of rotational speed of the turbine blades <NUM>. The blades <NUM> are configured to rotate, relative to the catheter <NUM> (<FIG>), at a rotational speed that is dependent, at least in part, on speed of the fluid <NUM> flowing through the blood vessel, and configuration of the duct <NUM> (if present), such as the taper of the duct <NUM>.

The signal generator <NUM> is configured to generate the signal <NUM> indicative of the rotational speed of the blades <NUM>. A signal lead <NUM>, exemplified by two electric wires <NUM> and <NUM>, is configured to carry the signal <NUM> to a tachometer <NUM>. The tachometer <NUM> is configured to measure the speed of the fluid <NUM> flow (flow rate) through the blood vessel, based on the signal <NUM>. In one embodiment, the tachometer <NUM> calculates the flow rate by multiplying the rotational speed of the blades <NUM> by a factor. The factor may represent a linear or non-linear relationship between rotational speed of the blades <NUM> and flow rate of the fluid <NUM>. This relationship may be determined empirically or by modeling the blades <NUM>, the fluid <NUM>, blood vessel geometry, friction, etc..

In one embodiment, schematically illustrated in <FIG>, the signal <NUM> indicative of the rotational speed of the turbine blades <NUM> is an AC signal, in which frequency of the signal <NUM> is proportional to the rotational speed of the blades <NUM> (not shown in <FIG> for clarity). In one such embodiment, the blades <NUM> are mechanically coupled to a magnet <NUM>, so the magnet <NUM> rotates with the blades <NUM>, as indicated by an arrow <NUM>. A coil <NUM> is disposed proximate the magnet <NUM>. Each revolution of the magnet <NUM> induces a pulse (in this example, one cycle <NUM> of a sine wave) of the signal <NUM>. The tachometer <NUM> may count the pulses (cycles) received during a predetermined time interval to measure the frequency of the signal <NUM>. Although the coil <NUM> is shown with a core, any suitable core, such as an iron core or an air core, may be used. In addition, although the coil <NUM> is shown split into two portions, the coil need not be split.

Alternatively, the tachometer <NUM> may measure voltage of the signal <NUM>, which is proportional to the rotational speed of the turbine blades <NUM>.

In another embodiment, schematically illustrated in <FIG>, the coil <NUM> (<FIG>) is replaced by a Hall effect sensor <NUM>. An output signal from the Hall effect sensor <NUM> may be processed by a threshold detector <NUM> (if needed) to generate the signal <NUM> indicative of the rotational speed of the turbine blades <NUM> (not shown in <FIG> for clarity). In this embodiment, the signal <NUM> consists of rectangular pulses <NUM>. As with the first embodiment described with respect to <FIG>, the frequency of the pulses <NUM> is proportional to the rotational speed of the blades <NUM>.

In yet another embodiment, schematically illustrated in <FIG>, the leads <NUM> and <NUM> from the coil <NUM> described with respect to <FIG> are connected to a light-emitting diode (LED) <NUM>. The LED <NUM> is optically coupled to a distal end of an optical fiber <NUM>. Each pulse (cycle) of the signal from the coil <NUM> causes the LED to flash, which sends an optical pulse along the optical fiber <NUM>. A series of these optical pulses collectively form the signal <NUM> indicative of the rotational speed of the blades <NUM>. Thus, in this embodiment, the optical fiber <NUM> is a lead <NUM> configured to carry the signal <NUM> to the tachometer <NUM>, and the tachometer <NUM> includes an optical sensor (not shown) to detect the optical pulses.

In any embodiment, the lead <NUM> configured to carry the signal <NUM> may be discrete and extend along a lumen of the catheter <NUM>. Alternatively, the lead <NUM> may be integral with the catheter <NUM>. For example, in some embodiments, the wires <NUM> and <NUM> are printed on an outside and/or inside surface of the catheter <NUM>, or imbedded within a wall of the catheter <NUM>. Similarly, in one embodiment, the optical fiber <NUM> is imbedded within the wall of the catheter <NUM>.

Although embodiments with one magnet per turbine have been described, each turbine can include more than one magnet, in which case the signal <NUM> may include more than one pulse per revolution of the blades <NUM>.

Although the heart pump pumps blood, the patient's heart action also pumps some blood. The total amount of blood flowing through the blood vessel is important to patient wellbeing. "Upstream" means in a direction opposite the direction of flow of blood or other fluid, and "downstream" means in the same direction as the flow of blood or other fluid. Advantageously, if the turbine is disposed a distance, in the upstream direction, from the heart pump inlet ports <NUM> (<FIG>) or a distance, in the downstream direction, from the heart pump outlet ports <NUM>, the blood flow rate measurement system embodiments described herein would measure total fluid flow in the blood vessel, not merely the amount of blood pumped by the heart pump. However, if the turbine is disposed between the heart pump inlet ports <NUM> and the heart pump outlet ports <NUM>, the blood flow rate measurement system would measure blood flow caused by heart action, plus additional blood flow around the heart pump caused by jet pumping driven by blood being ejected from the heart pump outlet ports <NUM>.

In some embodiments, the blades <NUM> are radially collapsible, i.e., in a direction toward the axis <NUM>. In some such embodiments, the blades <NUM> are made of a flexible material that can be folded, shrunk or compacted to reduce outside diameter <NUM> (<FIG>) of the blades <NUM>, at least while the catheter is being inserted into a blood vessel. In some embodiments, the blades <NUM> are resilient. In some embodiments, the blades <NUM> are made of a shape-memory material that rebounds to its memorized shape upon being heated to a temperature equal to, or slightly less than, the temperature of circulating blood in a human body. In some embodiments, each blade <NUM> includes a plurality of struts that collapse or expand, depending on the mode (collapsed or expanded) of the blade <NUM>. Consequently, once the catheter is in position, the blades <NUM> unfold or otherwise rebound into an efficient shape for being driven by flowing fluid in the blood vessel.

Any suitable structure and/or method may be used to initially make the blades <NUM> compact, to expand the blades <NUM> once the turbine <NUM> is in place, and to collapse the blades <NUM> in preparation for removal of the turbine <NUM>. Exemplary structures and methods are described in <CIT><CIT><CIT><CIT><CIT><CIT><CIT><CIT><CIT><CIT><CIT> and <CIT>, and <CIT><CIT> and<CIT>. 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 expand or compress impeller blades and/or pumps. The same wires or drive shafts may be used in similar ways to actuate a structure configured to expand and/or compress the blades <NUM> of the turbine <NUM>. Optionally or alternatively, different or additional wires or drive shafts may be used to actuate the structure configured to expand and/or compress the blades <NUM> of the turbine <NUM>. Optionally or alternatively, the lead <NUM> or part of the lead <NUM> may be used to actuate the structure configured to expand and/or compress the blades <NUM> of the turbine <NUM>.

While the invention is described through the above-described exemplary embodiments, modifications to, and variations of, the illustrated embodiments may be made without departing from the inventive concepts disclosed herein. For example, although specific parameter values, such as dimensions and materials, may be recited in relation to disclosed embodiments, within the scope of the invention, the values of all parameters may vary over wide ranges to suit different applications. Unless otherwise indicated in context, or would be understood by one of ordinary skill in the art, terms such as "about" mean within ±<NUM>%.

As used herein, including in the claims, the term "and/or," 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 all the items in the list. As used herein, including in the claims, the term "or," 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 all the items in the list. "Or" does not mean "exclusive or.

Although aspects of embodiments may be described with reference to flowcharts and/or block diagrams, functions, operations, decisions, etc. of all or a portion of each block, or a combination of blocks, may be combined, separated into separate operations or performed in other orders. References to a "module" are for convenience and not intended to limit its implementation. All or a portion of each block, module or combination thereof may be implemented as computer program instructions (such as software), hardware (such as combinatorial logic, Application Specific Integrated Circuits (ASICs), Field-Programmable Gate Arrays (FPGAs), processor or other hardware), firmware or combinations thereof.

The tachometer, heart pump control unit, or portions thereof, may be implemented by one or more processors executing, or controlled by, instructions stored in a memory. Each processor may be a general purpose processor, such as a central processing unit (CPU), a graphic processing unit (GPU), digital signal processor (DSP), a special purpose processor, etc., as appropriate, or combination thereof. However, once programmed with these instructions, the combination of the processor and the memory collectively form a special purpose processor.

The memory may be random access memory (RAM), read-only memory (ROM), flash memory or any other memory, or combination thereof, suitable for storing control software or other instructions and data. Instructions defining the functions of the present invention may be delivered to a processor in many forms, including, but not limited to, information permanently stored on tangible non-transitory non-writable storage media (e.g., read-only memory devices within a computer, such as ROM, or devices readable by a computer I/O attachment, such as CD-ROM or DVD disks), information alterably stored on tangible non-transitory writable storage media (e.g., floppy disks, removable flash memory and hard drives) or information conveyed to a computer through a communication medium, including wired or wireless computer networks. Moreover, while embodiments may be described in connection with various illustrative data structures, systems may be embodied using a variety of data structures.

Disclosed aspects, or portions thereof, may be combined in ways not listed above and/or not explicitly claimed. In addition, embodiments disclosed herein may be suitably practiced, absent any element that is not specifically disclosed herein. However, the invention is defined by the claims.

Claim 1:
A blood pump system comprising a heart pump and a blood flow rate measurement system, the blood flow measurement system comprising:
a catheter (<NUM>) including the heart pump and being configured to be inserted into a blood vessel of a living being;
a turbine (<NUM>) proximate a distal end of the catheter (<NUM>) and comprising at least one blade (<NUM>), the at least one blade (<NUM>) being configured to rotate, relative to the catheter, in response to fluid flow through the blood vessel and at a rotational speed dependent at least in part on speed of the fluid flow through the blood vessel;
a signal generator (<NUM>) mechanically coupled to the turbine (<NUM>) and configured to generate a signal (<NUM>) indicative of the rotational speed of the at least one blade (<NUM>); and
a signal lead (<NUM>) configured to carry the signal (<NUM>) indicative of the rotational speed of the at least one blade (<NUM>), the signal lead (<NUM>) being connected to the signal generator (<NUM>) and extending along the catheter (<NUM>).