INTRAVASCULAR BLOOD FLOW SENSING BASED ON VORTEX SHEDDING

Abstract

The invention relates to an intravascular blood flow sensor (200) comprising a guidewire or catheter (202) for intravascular insertion, and a vibration sensor (206) arranged and configured to provide a vibration sensor signal indicative of an oscillation frequency of blood flow propagating along a main direction (L) of intravascular blood flow. The vibration sensor comprises a flagellum (206.1) that extends from the catheter or guidewire (204) in the main direction of intravascular blood flow and is elastically deformable in a direction perpendicular to the main direction of intravascular blood flow by the blood flow oscillations.

Claims

1. An intravascular blood flow sensing device comprising: a guidewire or catheter for intravascular insertion and a vibration sensor arranged and configured to provide a vibration sensor signal indicative of an oscillation frequency of blood flow oscillations, wherein the vibration sensor comprises a flagellum that extends from the catheter or guidewire in the main direction of intravascular blood flow and is elastically deformable in the direction perpendicular to the main direction of intravascular blood flow, said direction of deformability, by the blood flow oscillations, wherein the flagellum comprises: an optical fiber segment configured to receive and guide light to and from a reflective fiber-segment tip, or an electro-active polymer material configured to generate and provide the vibration sensor signal in the form of a time-varying electrical signal depending on a deformation in the direction of deformability.

2. The intravascular device of claim 1, wherein the guidewire or catheter comprises a bluff part that is shaped for generation of vortices propagating along the main direction (L) of intravascular blood flow.

3. The intravascular device of claim 1, wherein the flagellum is less deformable in a second direction perpendicular to the main direction of intravascular blood flow than in the direction of deformability.

4. The intravascular device of claim 1, wherein the flagellum, in a non-deformed state, has a flat shape with a thickness in the direction of deformability that is smaller than a length extension in the main direction of intravascular blood flow, and smaller than a width extension in a direction perpendicular to the direction of deformability and to the main direction of intravascular blood flow.

5. The intravascular device of claim 1, wherein the flagellum is made of an electro-active polymer material and configured to generate and provide the vibration sensor signal in the form of a time-varying electrical signal having an amplitude depending on a deformation amount in the direction perpendicular to the main direction of intravascular blood flow.

6. The intravascular device of claim 1, wherein the flagellum is an optical fiber segment configured to receive and guide light to and from a reflective fiber-segment tip.

7. The intravascular device of claim 2, wherein the bluff part comprises a barrier section that protrudes from the catheter or guidewire in the direction perpendicular to the main direction of intravascular blood flow for generation of vortices propagating along the main direction of intravascular blood flow.

8. An intravascular blood flow sensor system comprising: an intravascular blood flow sensor according to claim 1; and a signal processing unit for determining a value of a blood flow quantity characterizing blood flow inside a blood vessel, the signal processing unit comprising: a vibration sensor signal input, which is configured to receive a vibration sensor signal from the intravascular vibration sensor, the vibration sensor signal comprising a vibration sensor signal component caused by blood flow oscillations of intravascular blood flow; and a blood flow determination unit which is configured, using the vibration sensor signal, to determine the vibration sensor signal component; using the vibration sensor signal component, to determine an oscillation frequency of the blood flow oscillations; and, using the determined oscillation frequency of the blood flow oscillations, to determine and provide the value of the blood flow quantity.

9. The intravascular system of claim 8, wherein the blood flow determination unit comprises a signal transformation unit, which is configured to determine a frequency-domain representation of the vibration sensor signal received during a predetermined measuring time span and to determine the oscillation frequency of the blood flow oscillations using the frequency-domain representation.

10. The intravascular system of claim 8, wherein the blood flow determination unit comprises a filter unit configured to filter out frequency components of the vibration sensor signal that are associated with a heartbeat frequency.

11. The intravascular system of claim 8, wherein the blood flow determination unit is further configured to hold or receive geometrical data indicative of a characteristic size of the blood vessel at a current intravascular position of the vibration sensor.

12. The intravascular system of claim 8, wherein the blood flow determination unit is configured to determine respective oscillation frequencies of the blood flow oscillations at at least two different measuring times and to determine and provide as an output a frequency ratio of the determined oscillation frequencies at the two measuring times as the value of the blood flow quantity.

13. The intravascular system of claim 8, further comprising a signal communication unit configured to receive the vibration sensor signals and to transmit the vibration sensor signals via a wireless carrier signal to the signal processing unit; wherein the signal processing unit is further configured to extract the vibration sensor signals from the carrier signal.

14. The intravascular system of claim 8, further comprising: a light source configured to provide light for coupling into the optical fiber segment; and a light sensor arranged to receive light reflected from the fiber-segment tip and modulated in intensity by oscillating deformation of the optical fiber segment, the light sensor being configured to provide the vibration sensor signal in the form of a light-sensor signal indicative of a time-varying reflected light intensity.

15. A method for controlling operation of an intravascular blood flow sensing system for determining a value of a blood flow quantity characterizing blood flow inside a blood vessel, the method comprising: receiving a vibration sensor signal from an intravascular device according to claim 1, the vibration sensor signal comprising a vibration sensor signal component caused by blood flow oscillations of intravascular blood flow; determining, using the vibration sensor signal, the vibration sensor signal component; determining, using the vibration sensor signal component, an oscillation frequency of the blood flow oscillations; and determining, using the oscillation frequency of the blood flow oscillations, and providing the value of the blood flow quantity.

16. The intravascular system of claim 12, wherein the blood flow quantity is a coronary flow reserve.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0066] In the following drawings:

[0067] FIG. 1A shows a schematic representation of a flow of a medium around stream-line shaped object;

[0068] FIG. 1B shows a schematic representation of the same flow of the medium around a bluff or barrier generating vortices in the flow;

[0069] FIG. 2 illustrates an embodiment of an intravascular blood flow sensor system comprising a signal processing unit and an intravascular blood flow sensor;

[0070] FIG. 3 shows another embodiment of an intravascular blood flow sensor system;

[0071] FIG. 4 shows another embodiment of an intravascular blood flow sensor system; and

[0072] FIG. 5 shows a flow diagram of a method for controlling operation of an intravascular blood flow sensor system.

DETAILED DESCRIPTION OF EMBODIMENTS

[0073] FIG. 1A and FIG. 1B show schematic illustrations of blood flow around a stream-line shaped object 100.a and around a bluff body 100.b in a blood vessel 101 at a fixed time. An incoming blood flow 102 in a main direction of blood flow that is indicated by the arrows 103 is the same in both figures and generally illustrated by straight flow lines upstream of the bluff body. In FIG. 1A, a stream-lined shape of the object 100.a does not generate vortices in the blood flow behind the object 104.a. In the case of FIG. 1B, the bluff body 100.b generates vortex shedding in the blood flow behind it.

[0074] Generally, vortex shedding is known per se as an oscillating flow that occurs under suitable circumstances when a fluid flows past a bluff body. The parameters relevant for vortex shedding to occur comprise a viscosity of the fluid, a flow velocity, as well as a size and shape of the object. The former can be characterized, for example, by a Reynolds number. The vortex shedding induced by the presence of the bluff body 100.b in the blood flow 102 generates a so-called Krmn vortex street 104.b downstream of the bluff body 100.b. Existing vortices propagate to positions further away from the bluff body along the main direction of blood flow indicated by the arrows 102, while new vortices are generated close to the body 100.b. Vortices are generated at alternating sides of the body and are associated with oscillations in the blood flow in a direction perpendicular to the main flow direction. At a given time, the vortices generated are distributed as exemplarily shown in FIG. 1B.

[0075] It is noted that the use of vortex-generated blood flow oscillations forms an advantageous embodiment. However, blood flow oscillation generated by other causes can be used to the same effect in other embodiments. The generation of such blood flow oscillations may be due to the inserted guidewire or catheter, or it may be due to intrinsic causes such as the geometry of the blood vessel. The present description of embodiments with reference to the drawings focuses in some parts on the example of vortex-generated oscillations without intention to thereby restrict the scope of the invention to such cases.

[0076] FIG. 2 is a schematic illustration of an embodiment of an intravascular blood flow sensor system 200 for measuring blood flow inside a blood vessel 201. The intravascular blood flow sensor system 200 comprises an intravascular blood flow sensor 203 that includes an intravascular guidewire 202 that has a guidewire body 204 with an atraumatic tip section 204.1. This particular intravascular blood flow sensor comprises a bluff part 205 that is suitably shaped for generation of vortices propagating along a main direction L of intravascular blood flow. It is noted that the bluff part 205 of the intravascular blood flow sensor need not necessarily be different in shape from other parts of the guide wire body 204 for enabling the formation of vortices. However, to facilitate reliable generation of vortices even at low blood flow velocities, it is advantageous to add features that shape the body of a typical guide wire or catheter in a less stream-lined way, such as for example providing a guidewire or a catheter comprising a bluff part.

[0077] The guidewire body 204 may have a rotational symmetry along its longitudinal direction, which in FIG. 2 corresponds to the direction L. However, in other embodiments (not shown), the generation of vortices is alternatively or additionally made possible or enhanced by providing a shape of the microcatheter or guidewire that exhibits a break of a rotational symmetry in at least part of the tip.

[0078] The tip section 204.1 includes a vibration sensor 206. The vibration sensor 206 comprises a flagellum 206.1 extending from a front surface of the tip section 204.1 in the main direction L of the intravascular blood flow. The flagellum 206.1 is elastically deformable in a direction P perpendicular to L which in the present example are the two mutually opposite directions P. An oscillating bending motion of the flagellum 206.1 in the direction P is driven by the vortex-generated oscillating motion of blood, as explained with reference to FIG. 1B. At a given time, the propagating vortices thus show a respective distribution that alternates vortices at different downstream positions of the tip section 204.1 in the longitudinal direction L (as exemplarily shown in FIG. 1B). Vortex-generated oscillations may occur in any direction that is perpendicular to the longitudinal direction L. By providing flagellums that are less deformable in a second direction perpendicular to the main direction of intravascular blood flow than in the direction of deformability, preferred deformation directions of the flagellum are achieved. Particularly suitable are with flagellums that in a non-deformed state, have a flat shape with a thickness in the direction of deformability that is smaller than a length extension in the main direction of intravascular blood flow and smaller than a width extension in a direction perpendicular to the direction of deformability and to the main direction of intravascular blood flow. Preferably, the length of the flagellum in the main direction of intravascular blood flow is at least five times longer than its width, which in turn is at least five times longer than its thickness.

[0079] In a real 3D vessel, more complex vortex configurations are possible that cannot be faithfully represented in a 2D illustration such as FIGS. 1A and 1B. The vibration sensor is thus configured to provide a vibration sensor signal indicative of the blood flow oscillations, but not necessarily of the propagation direction of the vortices.

[0080] The flagellum 206.1 is shown in FIG. 2 in two different phases of an oscillating bending motion corresponding to two different bending positions of the flagellum 206.1. A first phase of the oscillating motion is represented by a solid line, and a second phase is represented by a dotted line.

[0081] The flagellum 206.1 comprised by the vibration sensor 206 can be made of an electro-active polymer material and configured to generate and provide the vibration sensor signal in the form of a time-varying electrical signal having an amplitude depending on a deformation amount in the direction perpendicular to the main direction of intravascular blood flow.

[0082] In other blood flow sensors, the flagellum is an optical fiber segment configured to receive and guide light to and from a reflective fiber-segment tip

[0083] The intravascular blood flow sensor system 200 also comprises a signal processing unit 208 for determining a value of a blood flow quantity characterizing blood flow inside a blood vessel. The signal processing unit comprises a vibration sensor signal input 211 receives the vibration sensor signals from the vibration sensor of the intravascular blood flow sensor. The vibration sensor signal comprises a vibration sensor signal component caused by vortex-generated blood flow oscillations of intravascular blood flow. In general, the vibration sensor signal component caused by the vortex-generated blood flow oscillations is a component in a direction perpendicular to the main direction of blood flow. The signal processing unit 208 further comprises a blood flow determination unit 213 with is configured to determine the vibration sensor signal component using the vibration sensor signal, to determine the oscillation frequency of the vortex-generated blood flow oscillations using the vibration sensor signal component, and to determine and provide the value of the blood flow quantity using the determined oscillation frequency. In this exemplary signal processing unit 208 these three distinct tasks are performed by three respective units 213.1, 213.2 and 213.3. In other signal processing units, the three described tasks are performed by a processor.

[0084] Some signal processing units include a blood flow determination unit that additionally comprises a signal transformation unit (212), which is configured to determine a frequency-domain representation of the vibration sensor signal received during a predetermined measuring time span and to determine the oscillation frequency of the vortex-generated blood flow oscillations using the frequency-domain representation. To this end, the signal transformation unit 212 receives the vibration sensor signals from the vibration sensor signal input over a predetermined measuring time span associated with a given measuring time. The signal transformation unit 212 determines the oscillation frequency for the given measuring time using a frequency-domain representation of the vibration sensor signal during the respective measuring time span. Suitably, the signal transformation unit 212 is a Fast Fourier Transform unit that determines the Fourier Transform of the vibration sensor signal. From the transformed vibration sensor signal, an oscillation frequency can be determined in a simple manner as a frequency of a Fourier component having a maximum amplitude in an expected oscillation frequency range above 100 Hz, typically in the range of a few hundred Hz.

[0085] To make detection of the oscillation frequency easier, some signal processing units of the present embodiment further comprises a filter unit 214 that is configured to filter out frequency components from the vibration sensor signal that are associated with heart beat frequency. The heart beat frequency range is typically below 100 Hz.

[0086] Some signal processing unit further determines a frequency ratio of the determined oscillation frequencies at two measuring times. This way, blood flow quantities can be determined. Such blood flow quantities provide important information regarding the current physiological state of a blood vessel, and assist in the identification and quantitative characterization of a stenosis. For calculation and output of the CFR value, the measurements are made in a state of hyperemia and in a state of normal blood flow (e.g., at rest). The coronary flow reserve (CFR) is then determined and provided by the signal-processing unit with particular ease and reliability as the frequency ratio of respective vibration sensor signals at the measuring time corresponding to the state of hyperemia and at the measuring time corresponding to the state of normal blood flow.

[0087] In some signal processing units, a user interface 210 is provided for user input of control signals, such as for triggering the oscillation measurements by controlling the operation of the vibration sensor signal input, and for output of the value of the blood flow quantity determined. The user interface is in some embodiments used to provide geometrical data indicative of a characteristic size of the blood vessel at a current intravascular position of the intravascular blood flow sensor, which is required to provide a value of a flow velocity according to:

[00003]$v=\frac{f.Math.d}{S},$

wherein
v is the flow velocity;
f is the determined oscillation frequency of the vortex-generated blood flow oscillation;
d is the characteristic size of the blood vessel; and
S is a constant representing the Strouhal number applicable to blood flow in the given blood vessel.

[0088] In other signal processing units, the geometrical data is locally stored in a storage unit 215 which is accessed by the blood flow determination unit 213 for determining the value of the flow velocity v.

[0089] In other embodiments, the signal processing unit receives the geometrical data from an external imaging device or an external image processing device that is configured to image the blood vessel at a current intravascular position of the intravascular blood flow sensor and to determine and provide the geometrical data at that position.

[0090] As another mode of operation, which is available to a user as an alternative to the CFR determination, the signal processing unit 208 determines and provides relative changes in blood flow over time from a sequence of measurements, as compared to a first measurement of the sequence that can be triggered by user input.

[0091] FIG. 3 shows another embodiment of the intravascular blood flow sensor system 300. The following discussion will be focused on the differences between the intravascular blood flow sensor system 200 of FIG. 2 and the intravascular blood flow sensor system 300 of FIG. 3. Identical features are thus be referred to using the same numerals, except for the first digit, which is 2 for the features of the intravascular blood flow sensor system 200 of FIG. 2 and 3 for the features of the intravascular blood flow sensor system 300 of FIG. 3.

[0092] The flagellum 306 comprised by the vibration sensor 303 is an optical fiber segment 320 configured to receive and guide light to and from a reflective fiber-segment tip. The signal processing unit 308 of this particular intravascular flow sensors system 300 also comprises a light source 322 that is configured to provide light for coupling into the fiber segment and a light sensor 324 arranged to receive light reflected from the fiber-segment tip and modulated in intensity by oscillating deformation of the fiber segment. The light sensor is configured to provide the vibration sensor signal in the form of an electronic light-sensor signal indicative of a time-varying reflected light intensity.

[0093] A further variant of the intravascular blood flow sensor of FIGS. 2 and 3, which is not shown, comprises, instead of the guidewire 202, 302, a microcatheter provided with the flagellum-type vibration sensor 206, 306 in its tip section. The above description is otherwise equally applicable to that variant.

[0094] FIG. 4 shows a further embodiment of an intravascular blood flow sensor system 400 having an intravascular blood flow sensor 403 in an inserted state inside a blood vessel 401. The blood flow sensor 403 comprises a guidewire 402 with a guidewire body 404. The blood flow sensor 403 also comprises a vibration sensor 406 comprising a flagellum implemented as a vibration sensor discussed with reference to the embodiments of FIGS. 2-3. As visible from FIG. 4, no bluff part is used in this embodiment.

[0095] The blood flow sensor 403 further comprises a signal communication unit 408 that is configured to receive the vibration sensor signals from the vibration sensor 406 and to perform wireless transmission of the vibration sensor signals to the signal processing unit 410 using a carrier signal. The signal processing unit 410 has a corresponding signal communication unit, of which only an antenna 411 is shown, that is configured to receive the carrier signal and to extract the vibration sensor signals from the carrier signal. The signal processing unit 410 then determines the oscillation frequencies of vortex-generated blood flow oscillations and determines and provides the value of the blood flow quantity using the determined oscillation frequency of the vortex-generated blood flow oscillations. A user may interact with the blood flow sensor 403 via a user interface 412, as explained above. The user input may also be provided using wireless communication.

[0096] As shown in FIG. 4, the signal communication unit 408 is to be located outside the living being under examination. However, in a variant (not shown), the signal communication unit 408 is integrated into the guidewire body 404 and thus inserted in the blood vessel during operation. In these cases, the transmission of the vibration sensor signals is suitably performed using radio communication protocols such as for example any of the IEEE 801.11 standards for wireless communication, a Bluetooth-based wireless communication protocol, or any other radio-based wireless communication protocol.

[0097] FIG. 5 shows a flow diagram of a method 500 for controlling operation of an intravascular blood flow sensor system for determining a value of a blood flow quantity characterizing blood flow inside a blood vessel. The method comprises a step 502 in which a vibration sensor signal from an intravascular blood flow sensor is received, the vibration sensor signal comprising a vibration sensor signal component caused by vortex-generated blood flow oscillations of intravascular blood. In a step 504, the vibration sensor signal component is determined using the vibration sensor signal. In a step 506, an oscillation frequency of the vortex-generated blood flow oscillations is determined using the vibration sensor signal component. In a final step 508, the value of the blood flow quantity is determined and provided using the oscillation frequency of the vortex-generated blood flow oscillations.

[0098] In summary, an alternative intravascular blood flow sensor has been disclosed, comprising a guidewire or catheter for intravascular insertion having a bluff part that is shaped for generation of vortices propagating along a main direction of intravascular blood flow, and a vibration sensor arranged and configured to provide vibration sensor signal indicative of an oscillation frequency of vortex-generated blood flow oscillations. The vibration sensor comprises a flagellum that extends from the catheter or guidewire in the main direction of intravascular blood flow and is elastically deformable in the direction perpendicular to the main direction of intravascular blood flow by the vortex-generated blood flow oscillations.

[0099] Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims.

[0100] In the claims, the word comprising does not exclude other elements or steps, and the indefinite article a or an does not exclude a plurality.

[0101] A computer program may be stored/distributed on a suitable medium, such as an optical storage medium or a solid-state medium, supplied together with or as part of other hardware, but may also be distributed in other forms, such as via the Internet or other wired or wireless telecommunication systems.

[0102] Any reference signs in the claims should not be construed as limiting the scope.