Patent Description:
The severity of a stenosis or lesion in a blood vessel may be assessed by obtaining proximal and distal pressure measurements relative to the given stenosis and using those measurements for calculating a value of a Fractional Flow Reserve (FFR). FFR is defined as the ratio of a first or distal pressure Pd measured on the distal side of the stenosis and to a second or proximal pressure Pa measured on the proximal side of the stenosis, usually within the aorta. Conventionally, a sensor is placed on a distal portion of a guidewire or FFR wire to obtain the distal pressure Pd, while an external pressure transducer is fluidly connected via tubing to a guide catheter for obtaining the proximal, or aortic (AO) pressure Pa. Calculation of the FFR value provides a stenosis specific index of the functional severity of the stenosis in order to determine whether the blockage limits blood flow within the vessel to an extent that treatment is needed. An optimal or normal value of FFR in a healthy vessel is <NUM>, while values less than about <NUM> are generally deemed significant and in need of an interventional treatment. Common interventional treatment options include balloon angioplasty and/or stent implantation.

If an interventional treatment is required, the interventional device, such as a balloon catheter, is tracked over a guidewire to the site of the stenosis. Conventional FFR wires generally are not desired by clinicians to be used as guidewires for such interventional devices. Accordingly, if an interventional treatment is required, the clinician generally removes the FFR wire, inserts a conventional guidewire, and tracks the interventional device to the treatment site over the conventional guidewire.

To address this concern, efforts have been made to utilize catheters (micro-catheters) to take pressure measurements for calculating FFR. Using a catheter with a pressure sensor mounted within a distal shaft to measure the distal pressure Pd, a clinician may use a preferred guidewire for tracking the FFR catheter to the site of the stenosis. If an interventional treatment is required, the guidewire used with the catheter may remain in situ and the interventional device may be tracked over the existing guidewire to the site of the stenosis.

However, the pressure sensor mounted to the distal shaft of the catheter is generally exposed to provide access to the surrounding blood flow. The pressure sensor is a sensitive device and may be damaged by contact during handling or contact with tissue during advancement of the FFR catheter through the tortuous vasculature of a patient before positioning at the desired treatment site. Contact damage may result in errors in the measured distal pressure Pd.

While placing the pressure sensor within the distal shaft may protect the sensor from contact damage, manufacturing of the distal shaft in this configuration is difficult. For example, threading of the sensor wire though the distal shaft, mounting of the pressure sensor, and connection of the sensor wire to the pressure sensor in a confined space inside the distal shaft during manufacturing provides both build and maintenance challenges.

Additionally, as the distal shaft of the FFR catheter advances through the tortuous vasculature of the patient on its way to the desired treatment site, the distal shaft encounters bending forces as it winds its way to the targeted stenosis. When the distal shaft encounters these bending forces, the distal shaft and the pressure sensor mounted within can bend, damaging the delicate electronic pressure sensor. Bending force damage may result in errors in the measured distal pressure Pd.

Accordingly, there is a need for systems, and methods for manufacturing such systems, to reduce the occurrence of contact and bending force damage to a pressure sensor of a distal shaft of a FFR catheter. Document <CIT> relates to a pressure measuring catheter having reduced error from bending stresses.

Embodiments hereof relate to a distal shaft for measuring a pressure distal of a as defined in claim <NUM>.

Embodiments hereof also relate to a system for calculating a Fractional Flow Reserve of a stenosis in a blood vessel as defined in claim <NUM>.

Embodiments hereof also relate to a method of manufacturing a distal shaft of an FFR catheter for measuring a distal pressure measurement on a distal side of a stenosis as defined in claim <NUM>.

Specific embodiments of the present invention are now described with reference to the figures, wherein like reference numbers indicate identical or functionally similar elements. The terms "distal" and "proximal", when used in the following description to refer to a catheter or delivery system are with respect to a position or direction relative to the treating clinician. Thus, "distal" and "distally" refer to positions distant from, or in a direction away from the treating clinician, and the terms "proximal" and "proximally" refer to positions near, or in a direction toward the clinician. The terms "distal" and "proximal" used in the following description to refer to a vessel or a stenosis are used with reference to the direction of blood flow. Thus, "distal" and "distally" refer to positions in a downstream direction with respect to the direction of blood flow, and the terms "proximal" and "proximally" refer to positions in an upstream direction with respect to the direction of blood flow.

Although the description of the invention is in the context of treatment of blood vessels such as the coronary arteries, the invention may also be used in any other body passageways where it is deemed useful such as but not limited to peripheral arteries, carotid arteries, renal arteries, and/or venous applications.

<FIG> is a schematic partial side and partial perspective illustration of a system <NUM> for calculating a Fractional Flow Reserve (FFR) according to an embodiment hereof. The system <NUM> includes an FFR catheter or micro-catheter <NUM>, a proximal pressure-sensing device (not shown), and a processing device <NUM>. The catheter <NUM> is configured to be disposed with a proximal portion thereof extending outside of a patient and a distal portion thereof positioned in situ within a lumen <NUM> of a vessel <NUM> having a stenosis <NUM>. In an embodiment, the vessel <NUM> is a blood vessel such as but not limited to a coronary artery. The stenosis <NUM> is generally representative of any blockage or other structural arrangement that results in a restriction to the flow of fluid through a lumen <NUM> of the vessel <NUM>. The stenosis <NUM> may be a result of plaque buildup, including without limitation plaque components such as fibrous, fibro-lipidic (fibro fatty), necrotic core, calcified (dense calcium), blood, fresh thrombus, and mature thrombus. Generally, the composition of stenosis <NUM> will depend on the type of vessel being evaluated. In that regard, it is understood that embodiments hereof are applicable to various types of blockages or other narrowing of a vessel that results in decreased fluid flow.

The catheter <NUM> includes a proximal shaft <NUM> and a distal shaft <NUM>. A pressure sensor <NUM>, shown in <FIG> and in greater detail in <FIG>, is disposed in a housing <NUM> of the distal shaft <NUM>. The pressure sensor <NUM> is coupled to the housing <NUM> and covered by a cover <NUM>, as described in greater detail below. The cover <NUM> is configured to protect the pressure sensor <NUM> during handling and use of the catheter <NUM>. The cover <NUM> is a separate piece attached to the housing <NUM> during manufacture to simplify manufacturing of the distal shaft <NUM> with the pressure sensor <NUM> disposed therein. As used herein, the term "separate" when used to describe that the cover <NUM> is a "separate" piece attached to the housing <NUM> during manufacture, it is meant that the cover <NUM> is not formed as part of the housing <NUM>. Instead, the two pieces are separate and then are attached as described below during manufacture. Thus, for example, and not by way of limitation, a housing that is formed with a portion covering a pressure sensor would not be a "separate" cover. Similarly, a "cover" that is co-formed with a "housing", such as by molding, is not considered a separate cover attached to the housing.

In the embodiment shown in <FIG>, catheter <NUM> includes a guidewire lumen <NUM> extending through the proximal shaft <NUM> and the distal shaft <NUM>. The guidewire lumen is configured to receive a guidewire <NUM>. However, instead of the over-the-wire configuration shown in <FIG>, catheter <NUM> may have a rapid exchange configuration wherein the guidewire lumen <NUM> extends through the distal shaft <NUM> and a portion of the proximal shaft <NUM>, and the guidewire <NUM> exits through a rapid exchange port (not shown) in a distal portion of the proximal shaft <NUM>, as would be understood by those skilled in the art. Catheter <NUM> also includes a sensor wire lumen <NUM> extending through the proximal shaft <NUM> and the distal shaft <NUM> to the pressure sensor <NUM>. The proximal shaft <NUM> includes a proximal end <NUM> coupled to a hub or luer <NUM> and a distal end <NUM> coupled to the distal shaft <NUM>.

In an embodiment, the distal shaft <NUM> of the catheter <NUM> includes a proximal end <NUM> coupled to a distal end <NUM> of the proximal shaft <NUM>, and a distal end <NUM>, as shown in <FIG>. A distal portion of the guidewire lumen <NUM> extends through the distal shaft <NUM>. The distal shaft <NUM> includes the housing <NUM>, the pressure sensor <NUM>, the cover <NUM>, a distal tip <NUM>, and an aperture <NUM> through the distal tip <NUM>, as described in more detail below. The distal shaft <NUM> is configured such that the pressure sensor <NUM> and the tip <NUM> are disposed on the distal side <NUM> of the stenosis <NUM> such that the pressure sensor <NUM> can measure a distal pressure Pd distal of the stenosis <NUM>, as shown in <FIG>.

In an embodiment, the housing <NUM> of the distal shaft <NUM> is of a generally tubular shape having a proximal end <NUM> coupled to the distal end <NUM> of the proximal shaft <NUM> and a distal end <NUM> coupled to the distal tip <NUM>, as shown in <FIG> and <FIG>. The housing <NUM> defines an open seat <NUM>, extending from an outer surface of the housing <NUM> inward. In particular, referring to <FIG>, the open seat <NUM> may be defined by groove or depression <NUM> in the housing <NUM>. The open seat <NUM> is configured to receive the pressure sensor <NUM> therein. The open seat <NUM> is further configured to receive a fluid therein from the aperture <NUM>, as described in greater detail below. The housing <NUM> may be formed of polymeric materials, non-exhaustive examples of which include polyethylene, polyether block amide (PEBA), polycarbonate, acrylonitrile butadiene styrene (ABS), polyether ether ketone (PEEK), polyamide and/or combinations thereof, either blended or co-extruded. The housing <NUM> may be coupled to the distal end <NUM> of the proximal shaft <NUM> and a proximal end <NUM> of the tip <NUM> by methods such as, but not limited to adhesives, fusing, welding, or any other method suitable for the purposes described herein. Alternatively, the housing <NUM> may be formed as an integral component of the proximal shaft <NUM> and the tip <NUM>. The open seat <NUM> is shown as a generally rectangular cuboid. However, this is not meant to be limiting and open seat <NUM> may be of any shape to house the pressure sensor <NUM> and provide sufficient space for fluid entering therein for the pressure sensor <NUM> to measure a pressure of the fluid.

The pressure sensor <NUM> includes a pressure-sensing surface <NUM>, as shown in <FIG>, <FIG>, and <FIG>. The pressure sensor <NUM> may be a piezo-resistive pressure sensor, a piezo-electric pressure sensor, a capacitive pressure sensor, an electromagnetic pressure sensor, an optical pressure sensor, and/or combinations thereof suitable for the purpose described herein. While the pressure sensor <NUM> is shown in <FIG> configured with the pressure-sensing surface <NUM> facing radially outward, the pressure-sensing surface <NUM> may face in other directions such that pressure-sensing surface <NUM> measures distal pressure Pd of a fluid outside the distal shaft <NUM> that has entered the open seat <NUM> through the aperture <NUM>. The pressure sensor <NUM> is further configured to communicate a measured distal pressure Pd with the processing device <NUM> through the pressure sensor wire(s) <NUM>, as described in <CIT> The pressure sensor <NUM> is disposed within and coupled to the open seat <NUM> of the housing <NUM>. The open seat <NUM> and/or the pressure sensor <NUM> may include tabs, arms, slots, or other devices suitable to enhance coupling of the pressure sensor <NUM> in the open seat <NUM>. The pressure sensor <NUM> may be coupled to the open seat <NUM>, for example, and not by way of limitation, by adhesives, fusing, welding, or any other method suitable for the purposes of the present disclosure. The pressure sensor <NUM> is further coupled to the pressure sensor wire(s) <NUM>. The pressure sensor <NUM> may be coupled to pressure sensor wire(s) <NUM> for example, and not by way of limitation, by soldering, fusing, welding, for any other method suitable for the purposes of the present disclosure.

In an embodiment, the tip <NUM> is of a generally frusto-conical shape. The tip <NUM> includes the proximal end <NUM> coupled to the distal end <NUM> of the housing <NUM>, and a distal end <NUM>, as shown in <FIG> and <FIG>. The tip <NUM> may be formed of of polymeric materials, non-exhaustive examples of which include polyethylene, polyether block amide (PEBA), polycarbonate, acrylonitrile butadiene styrene (ABS), polyether ether ketone (PEEK), polyamide and/or combinations thereof, or other materials suitable for the purposes described herein. Alternatively, the tip <NUM> may be formed as an integral component of the housing <NUM> of the distal shaft <NUM>.

In an embodiment, the distal shaft <NUM> further includes the aperture <NUM> disposed through the tip <NUM> and in fluid communication with the open seat <NUM>. The aperture <NUM> is generally aligned with the open seat <NUM>. The aperture <NUM> is an opening extending from an outer surface <NUM> of the tip <NUM>, through tip <NUM>, and extends into the open seat <NUM> of the housing <NUM>. The aperture <NUM> is configured to receive fluid therethrough such that the fluid outside the distal tip <NUM> may flow through the aperture <NUM> and into the open seat <NUM> of the housing <NUM>. The fluid flows through the aperture <NUM> and into the open seat <NUM> such that the fluid is in contact with the pressure-sensing surface <NUM> of the pressure sensor <NUM>. In an embodiment, the aperture <NUM> is aligned generally parallel to a central longitudinal axis LA1 of the distal shaft <NUM> such that the aperture <NUM> provides axial fluid flow to the open seat <NUM> and the pressure sensor <NUM> disposed therein. <FIG> shows an aperture central axis LA2 parallel to the central longitudinal axis LA1 of the distal shaft <NUM>. The aperture <NUM> is sized such that a sufficient amount of blood flows into the open seat <NUM> of the housing <NUM> but tissue is prevented from entering the open seat <NUM> during advancement of the distal shaft <NUM> through a vasculature. In an embodiment, the aperture <NUM> is in the range of <NUM> to <NUM> microns. The aperture <NUM> may be formed as an integral component of the distal tip <NUM> or may be formed by removing material from the distal tip <NUM> by any suitable method such as, but not limited to cutting, machining, drilling, laser cutting, laser ablation, or other methods suitable for the purposes described herein. The aperture <NUM> is shown as generally tubular, but this is not meant to limit the design, and other shapes may be utilized. Moreover, while the aperture <NUM> is shown as a single aperture disposed through the tip <NUM>, this is not meant to limit the design, and other configurations may be used. For example, and not by way of limitation, there may be multiple apertures <NUM>. In another non-limiting example, the aperture <NUM> may be disposed through the cover <NUM>, as shown in <FIG>.

In an embodiment, the cover <NUM> is of a generally tubular shape with a proximal end <NUM>, a distal end <NUM>, and a cover lumen <NUM> extending through the cover <NUM> between the proximal and distal ends <NUM>, <NUM>, as shown in <FIG> and <FIG>. The cover <NUM> may be disposed in a first configuration, as shown in <FIG>, wherein the cover <NUM> is not coupled to the housing <NUM> and is disposed proximal to the housing <NUM>. The first configuration is used during manufacture to simplify installation of the sensor <NUM> and connection of the sensor <NUM> to the sensor wire(s) <NUM>. The cover <NUM> is moved during manufacturing to a second configuration, as shown in <FIG>, wherein the cover <NUM> is coupled to the housing <NUM> such that the housing <NUM> is disposed within the cover lumen <NUM>. As explained above, the cover <NUM> is configured to protect the pressure sensor <NUM> when the cover <NUM> is in the second configuration. More specifically, the cover <NUM> prevents contact damage to the pressure sensor <NUM> during handling, or contact with tissue during advancement of the catheter <NUM> through a vasculature of a patient. The cover <NUM> may be formed of a second material different than a first material of the housing <NUM> such that the cover <NUM> is more rigid than the housing <NUM>. The increased rigidity of the cover <NUM> resists bending of the distal shaft <NUM>, especially in areas adjacent to the cover <NUM>, as the distal shaft <NUM> advances through the vasculature of the patient. Thus, the more rigid cover <NUM> protects the pressure sensor <NUM> from bending damage or bending stresses incurred during handling or advancement through the vasculature of the patient. The cover <NUM> is coupled to housing <NUM> by a coupling mechanism such as, but not limited to a friction-fit mechanism, a snap-fit mechanism, adhesives, or any other coupling mechanism suitable for the purposes described herein. The cover <NUM> may be formed of metals such as, but not limited to, stainless steel, gold, platinum, and/or iridium, and alloys thereof. In some embodiments, such as forming the cover <NUM> of gold, platinum, platinum-iridium alloys, and other radiopaque materials, the cover <NUM> may also act as a marker band. In other embodiments, the cover <NUM> may be formed of metal reinforced polymers, polycarbonate, acrylonitrile butadiene styrene (ABS), polymers (e.g. polyether ether ketone (PEEK)), reinforced polymers (e.g. carbon fiber), or other materials suitable for the purposes described herein.

<FIG> and <FIG> show the cover <NUM> and the housing <NUM> with a snap-fit coupling mechanism according to an embodiment hereof. The snap-fit coupling mechanism includes a first annular ring <NUM> extending radially inward from an inside surface of the cover <NUM> and a corresponding second annular ring <NUM> extending radially outward from an outer surface of the housing <NUM>. The inner diameter D1 of the first annular ring <NUM> of the cover <NUM> in the first configuration is smaller than the outer diameter D2 of the corresponding second annular ring <NUM> of the housing <NUM>. When the cover <NUM> is moved distally in the direction of arrow <NUM> with sufficient force, the distal portion of the cover <NUM> deforms slightly radially outwardly for the first annular ring <NUM> of the cover <NUM> to move over the second annular ring <NUM> of the housing <NUM>. Upon clearing the second annular ring <NUM>, the cover <NUM> returns to its initial shape such that the first annular ring <NUM> is distal of the second annular ring <NUM>, as shown in <FIG>. This locks the cover <NUM> in place. The annular rings <NUM>, <NUM> may include angled faces such as to minimize the force required to move the cover <NUM> distally over the second annular ring <NUM> while preventing movement of the cover <NUM> in a proximal direction. Thus, the cover <NUM> has been transitioned from the first configuration to the second configuration. When in the second configuration, the distal end <NUM> of the cover <NUM> is adjacent to the proximal end <NUM> of the tip <NUM>, as shown in <FIG>. Moreover, when the cover <NUM> is in the second configuration, as shown in <FIG> and <FIG>, the cover <NUM> encircles an outer surface of the housing <NUM> and the pressure sensor <NUM>. The annular rings <NUM>, <NUM> are shown as being disposed at distal portions of the cover <NUM> and housing <NUM>, respectively. However, this is not meant to be limiting and annular rings may instead be disposed anywhere along the length of the cover <NUM> and the housing <NUM>. Further, the annular rings <NUM>, <NUM> do not need to extend around the entire circumference of the cover <NUM> and the housing <NUM>. Instead, the annular rings may be several protrusions or ring segments extending from the inner surface of the cover <NUM> and the outer surface of the housing <NUM>, with circumferential gaps between the ring segments. Further, adhesives or other coupled mechanisms may be added to the snap-fit coupling described. Still further, other snap-fit mechanisms suitable for the purposes described herein may be utilized.

<FIG> shows another embodiment of cover <NUM>' that may be used with the catheter <NUM> of <FIG>. The cover <NUM>' is similar to the cover <NUM> described previously, except that the cover <NUM>' utilizes a friction-fit coupling mechanism for coupling the cover <NUM>' to a housing <NUM>'. Other than the cover <NUM>' and the housing <NUM>', the remaining features of the catheter <NUM> remain as described above, and therefore will not be described here. In the embodiment shown, a distal portion of the cover <NUM>' has a first inner diameter D1 when the cover <NUM>' is in the first configuration. A corresponding distal portion of the housing <NUM>' has a second outer diameter D2, wherein the first diameter D1 is smaller than the second diameter D2. Thus, with cover <NUM>' in the first configuration disposed over the distal portion of the proximal shaft <NUM>, application of a sufficient force distally (in the direction of arrow <NUM>) to the cover <NUM>' will slide or translate the cover <NUM>' distally over the housing <NUM>'. More specifically, with a sufficient force applied thereto, the cover <NUM>' will radially expand to match the larger diameter outer surface of the housing <NUM>'. The cover <NUM>' will attempt to radially collapse to its original shape, thereby coupling the cover <NUM>' to the housing <NUM>' via a friction fit. While the friction fit coupling is described at the corresponding distal ends of the cover <NUM>' and the housing <NUM>', this is not meant to be limiting. Thus, the friction fit may be at the respective proximal ends or over an entire length of the cover <NUM>' and the housing <NUM>' Further, an adhesive or other coupling mechanism may be added to the friction fit coupling to further secure the cover <NUM>' to the housing <NUM>'.

Referring to <FIG>, another embodiment of an FFR catheter or micro-catheter <NUM> is shown. Catheter <NUM> includes a proximal shaft <NUM>, a distal shaft <NUM>, and a pressure sensor <NUM>. Further, the distal shaft <NUM> includes a housing including an open seat <NUM>, a distal tip <NUM>, and an aperture <NUM>. These components are similar to the components described above with respect to catheter <NUM>. Therefore, details and alternatives of these similar components will not be repeated. The embodiment of <FIG> differs from the embodiments of <FIG> in that the cover <NUM> is of a generally partial cylindrical shape. Further, the connection between the cover <NUM> and the housing <NUM> is different than the connection between the cover <NUM> and the housing <NUM>.

In an embodiment, the cover <NUM> is of a generally partial cylindrical shape. The cover <NUM> includes a proximal end <NUM>, a distal end <NUM>, a first circumferential edge <NUM>, and a second circumferential edge <NUM>, as shown in <FIG> and <FIG>. An outer surface <NUM> and an inner surface <NUM> of the cover <NUM> are defined between the proximal end <NUM>, the distal end <NUM>, the first circumferential edge <NUM>, and the second circumferential edge <NUM>, as shown in <FIG>. The outer and inner surfaces <NUM>, <NUM> define a partial cylinder with an open portion <NUM> adjacent the inner surface <NUM>, opposite the outer surface <NUM>. The cover <NUM> includes a first configuration wherein the cover <NUM> is not coupled to the housing <NUM>, as shown in <FIG>, and a second configuration wherein the cover <NUM> is coupled to the housing <NUM>, as shown in <FIG>. In the second configuration, the open portion <NUM> of the cover <NUM> is aligned with and covers the open seat <NUM> of the housing <NUM>, as shown in <FIG>. With the cover <NUM> in the first configuration and positioned over the housing <NUM> such that the open portion <NUM> of the cover <NUM> is aligned with the open space <NUM> of the housing <NUM>, the cover <NUM> may transition to the second configuration by moving the cover <NUM> towards the central longitudinal axis LA1 of the housing <NUM>, as indicated by arrow <NUM> in <FIG>. Stated another way, with the cover <NUM> in the first configuration and disposed over the corresponding open space <NUM> of the housing <NUM>, the cover <NUM> may be pressed down onto the housing <NUM> to transition to the second configuration, as shown in <FIG>.

The cover <NUM> is configured to protect the pressure sensor <NUM> when the cover <NUM> is in the second configuration, i.e., when the cover <NUM> is coupled to the housing <NUM>. More specifically, and as described previously, the cover <NUM> prevents contact damage to the pressure sensor <NUM> during handling, or contact with tissue during advancement of the catheter <NUM> through the vasculature of a patient. The housing comprises a first matarial and the cover comprises a second material that is stiffer than the first material. Thus, the cover <NUM> may be formed of a second material different than a first material of the housing <NUM> such that the cover <NUM> is more rigid than the distal housing <NUM>. The increased rigidity of the cover <NUM> resists bending of the distal shaft <NUM> as the distal shaft <NUM> advances through the vasculature of the patient. Thus, the more rigid cover <NUM> protects the pressure sensor <NUM> from bending damage or bending stresses incurred during handling or advancement through the vasculature of the patient. The cover <NUM> is coupled to the housing <NUM> by a coupling mechanism such as, but not limited to a friction-fit mechanism, a snap-fit mechanism, adhesives, or any other coupling mechanism suitable for the purposes described herein. The cover <NUM> may be formed of metals such as, but not limited to, stainless steel, gold, platinum, and/or iridium, and alloys thereof. In some embodiments, such as forming the cover <NUM> of gold, platinum, platinum-iridium alloys, and other radiopaque materials, the cover <NUM> may also act as a marker band. In other embodiments, the cover <NUM> may be formed of metal reinforced polymers, polycarbonate, acrylonitrile butadiene styrene (ABS), polymers (e.g. polyether ether ketone (PEEK)), reinforced polymers (e.g. carbon fiber), or other materials suitable for the purposes described herein.

<FIG> show the cover <NUM> with a friction-fit coupling mechanism according to an embodiment hereof. The cover <NUM> in the first configuration has a first distance D1 between the first circumferential edge <NUM> and the second circumferential edge <NUM>, as shown in <FIG>. The housing <NUM> includes a first shoulder <NUM> disposed in an outer surface <NUM> of the housing <NUM>, adjacent to the open seat <NUM>, and a second shoulder <NUM> disposed in the outer surface <NUM> of the housing <NUM>, adjacent to the open seat <NUM>, as shown in <FIG> and in greater detail in <FIG>. The first and second shoulders <NUM>, <NUM> extend inwardly from the outer surface <NUM> to first and second walls <NUM>, <NUM>, respectively, which extend generally perpendicular to first and second shoulders <NUM>, <NUM>, as shown in <FIG>. The housing <NUM> has a second distance D2 between outer surfaces of the first wall <NUM> and the second wall <NUM>, as shown in <FIG>. The second distance D2 is greater than the first distance D1 between the first and second circumferential edges <NUM>, <NUM> of the cover <NUM>. Thus, when the cover <NUM> is in the second configuration coupled to the housing <NUM>, the first circumferential edge <NUM> of the cover <NUM> is configured to align with and rest on the first shoulder <NUM> of the housing <NUM>. Similarly, the second circumferential edge <NUM> of the cover <NUM> is configured to align with and rest on the second shoulder <NUM> of the housing <NUM>. Because the first distance D1 between the first and second circumferential edges <NUM>, <NUM> is smaller than the second distance D2 between the outer surfaces of the walls <NUM>, <NUM>, the cover <NUM> expands slightly radially outward for the first and second circumferential edges <NUM>, <NUM> to clear the walls <NUM>, <NUM> and sit on the first and second shoulders <NUM>, <NUM>. The cover <NUM> wants to return to its undeformed shape. Thus, the cover <NUM> squeezes radially inwardly on the respective outer surfaces of first and second walls <NUM>, <NUM>, thereby creating a friction fit between the cover <NUM> and the housing <NUM>, as shown in <FIG>. An adhesive or other coupling mechanism may be added to the friction fit to further secure the cover <NUM> to the housing <NUM>.

<FIG> show a cover <NUM>' coupled to a housing <NUM>' with a snap-fit connection. The cover <NUM>' and the housing <NUM>' are similar to the cover <NUM> and the housing <NUM> of <FIG> except for the snap-fit connection.

Thus, the cover <NUM>' includes a first protrusion or lip <NUM>' extending generally radially inward from an inner surface of the cover <NUM>', adjacent to the first circumferential edge <NUM>'. A second protrusion or lip <NUM>' extends generally radially inward from the inner surface of the cover <NUM>', adjacent the second circumferential edge <NUM>'. The first and second protrusions <NUM>', <NUM>' are generally opposite each other and extend towards each other. Further, the first and second protrusions <NUM>', <NUM>' extend longitudinally along the first and second circumferential edges <NUM>, <NUM>. With the cover <NUM>' in the first configuration not coupled to the housing <NUM>', the cover <NUM>' has a first distance D1 between the first protrusion <NUM>' and the second protrusion <NUM>', as shown in <FIG>.

The housing <NUM>' of the distal shaft <NUM>' includes a first lip <NUM> extending radially outwardly from the first wall <NUM>' and a second lip <NUM> extending radially outwardly from the second wall <NUM>', as shown in <FIG>. Thus, a first channel <NUM> is formed between the first shoulder <NUM>' and the first lip <NUM> and a second channel <NUM> is formed between the second shoulder <NUM>' and the second lip <NUM>. The first protrusion <NUM>' fits within the first channel <NUM> of the housing <NUM>' and the second protrusion <NUM>' fits within the second channel <NUM> of the housing <NUM>'. Further, a second distance D2 between outer surfaces of the first and second lips <NUM>, <NUM> is larger than the first distance D1 between the first and second protrusions <NUM>', <NUM>' of the cover <NUM>'. Thus, when the cover <NUM>' is pushed towards the housing <NUM>' the cover <NUM>' expands radially outward for the first and second protrusions <NUM>', <NUM>' to clear the first and second lips <NUM>, <NUM> of the housing <NUM>'. The cover <NUM>' continues to be pushed towards the housing <NUM>' until the first and second protrusions <NUM>', <NUM>' clear the first and second lips <NUM>, <NUM>, respectively. The first and second protrusions <NUM>', <NUM>' then move radially inward into first and second channels <NUM>, <NUM>, respectively, as shown in <FIG>. The first and second lips <NUM>, <NUM> prevent the cover <NUM> from being lifted off of the housing <NUM>'. An adhesive or other coupling mechanism may be added to the snap-fit connection of <FIG> to further secure the cover <NUM>' to the housing <NUM>'.

As previously described, embodiments hereof may include more than one aperture disposed through the tip and/or the cover. Accordingly, another embodiment of a cover <NUM>" useful with the catheter <NUM> of <FIG> is shown in <FIG>. The catheter <NUM> includes a first aperture <NUM> disposed through the tip <NUM> and a second aperture <NUM>' disposed through the cover <NUM>". With the exception of the second aperture <NUM>' of the cover <NUM>", the remaining features of catheter <NUM> remain as described above, and therefore will not be repeated. In an embodiment, the second aperture <NUM>' is disposed through the cover <NUM>" and is in fluid communication with the open seat <NUM> of the housing <NUM>. The second aperture <NUM>' is an opening extending from an outer surface to an inner surface of the cover <NUM>" and extends into the open seat <NUM> of the housing <NUM>. The second aperture <NUM>' is configured to receive fluid therethrough such that fluid outside the cover <NUM>" may flow through the second aperture <NUM>' and into the open seat <NUM> of the housing <NUM>. Thus, fluid flows through both the first aperture <NUM> and the second aperture <NUM>' into the open seat <NUM> such that the fluid is in contact with the pressure-sensing surface <NUM> of the pressure sensor <NUM>. The first aperture <NUM> and the second aperture <NUM>' are sized such that a sufficient amount of blood flows into the open seat <NUM> of the housing <NUM> but tissue is prevented from entering the open seat <NUM> during advancement of the distal shaft <NUM> through a vasculature. The second aperture <NUM>' may be formed as an integral component of the cover <NUM>" or may be formed by removing material from the cover <NUM>" by any suitable method, non-limiting examples of which include cutting, machining, drilling, laser cutting; laser ablation, or other methods suitable for the purposes described herein. Although the second aperture <NUM>' is shown as generally tubular with oval opening, this is not meant to be limiting, and other shapes may be utilized. Moreover, while the cover <NUM>" is described herein with one (<NUM>) second aperture <NUM>', it will be understood that the cover <NUM>" may include more than one second aperture <NUM>' and that the second aperture(s) <NUM>' may be located at other locations of on the cover <NUM>". Additionally, while described herein as an additional aperture in the generally tubular cover <NUM>, it will be understood that an additional aperture or apertures may be disposed through embodiments of the partial cylindrical shaped cover <NUM> as well as in other embodiments of covers of the present disclosure.

With an understanding of the components above, it is now possible to describe their interaction as a system for measuring and calculating a Fractional Flow Reserve (FFR) according to an embodiment of the present disclosure. Referring to <FIG>, the system <NUM> is shown disposed through a guide catheter <NUM>, which is utilized as the proximal pressure-sensing device, as explained below. Referring to <FIG>, the guide catheter <NUM> and the guidewire <NUM> are advanced through the vasculature to a desired site. The guidewire <NUM> may be back-loaded into the FFR catheter <NUM> (i.e., the proximal end of the guidewire <NUM> is loaded into the distal end of guidewire lumen <NUM> at the distal end <NUM> of the distal shaft <NUM>). The FFR catheter <NUM> may then be advanced over the guidewire <NUM> and through a lumen <NUM> of the guide catheter <NUM> to the desired treatment site. In particular, with a distal end <NUM> of the guide catheter <NUM> disposed at a desired site proximal of the stenosis <NUM>, such as in the sinus <NUM>, the distal shaft <NUM> of the FFR catheter <NUM> is advanced through the lumen <NUM> and distal of the distal end <NUM> of the guide catheter <NUM>. The FFR catheter <NUM> is advanced such that the distal shaft <NUM> is disposed through the stenosis <NUM> of the vessel <NUM>. Blood flow from the aortic sinus <NUM> fills the lumen <NUM> and tubing <NUM> via a port <NUM> of a proximal portion <NUM> of the guide catheter <NUM>. The blood pressure Pa at the distal end <NUM> of the guide catheter <NUM> is measured by an external pressure transducer <NUM> via the fluid (blood) column extending through the lumen <NUM> and the tubing <NUM>. Thus, the external pressure transducer <NUM> is configured to measure proximal, or aortic (AO) pressure Pa at the distal end <NUM> of the guide catheter <NUM>.

The external pressure transducer <NUM> is configured to communicate measured the proximal pressure Pa to the processing device <NUM> via a pressure transducer wire <NUM>, as shown in <FIG>. While the pressure transducer <NUM> is shown in <FIG> as communicating the measured proximal pressure Pa with the processing device <NUM> via the pressure transducer wire <NUM>, this is not meant to limit the design and the pressure transducer <NUM> may communicate with the processing device <NUM> by any means suitable for the purposes described, including, but not limited to, electrical cables, optical cables, or wireless devices.

Simultaneously, blood on the distal side <NUM> of the stenosis <NUM> flows through the aperture <NUM> of the tip <NUM> and into the open seat <NUM> (<FIG>) of the housing <NUM>. The blood within the open seat <NUM> (<FIG>) is in contact with the pressure-sensing surface <NUM> of the pressure sensor <NUM>, coupled therein. The pressure within the open seat <NUM> is equal to the pressure on the distal side <NUM> of the stenosis <NUM>. Thus, the distal pressure Pd is sensed by the pressure sensor <NUM>. The sensed distal pressure Pd is communicated with the processing device <NUM>. The processing device <NUM> calculates the Fractional Flow Reserve (FFR) based on the measured distal pressure Pa divided by the measured proximal/aortic pressure Pa, or FFR = Pd/Pa.

Although the method described above refers to the FFR catheter <NUM>, it applies equally to catheter <NUM> and to variations described above with respect to the catheters <NUM>, <NUM>.

Referring to <FIG>, a method of manufacturing a distal shaft <NUM> of an FFR catheter for measuring a distal pressure measurement on a distal side of a stenosis according to an embodiment hereof is described. Steps <NUM>-<NUM> of <FIG> reference the cover <NUM> and the distal shaft <NUM> components shown in <FIG>. The cover <NUM> of <FIG> includes the cover lumen <NUM> configured to receive the housing <NUM> of the distal shaft <NUM> therein.

In step <NUM>, the cover <NUM> is positioned over the proximal shaft <NUM> proximal of the housing <NUM> of the distal shaft <NUM>.

In step <NUM>, a sufficient force is applied distally to the cover <NUM> to distally slide or translate the cover <NUM> over the housing <NUM> of the distal shaft <NUM>.

In step <NUM>, the force is applied distally to the cover <NUM> such that the coupling mechanism of the distal shaft <NUM> is engaged and the cover <NUM> is coupled to the housing <NUM> of the distal shaft <NUM>.

In step <NUM>, the aperture <NUM> is created in the tip <NUM> extending from an outer surface of the tip <NUM> to the open seat <NUM> of the housing <NUM>.

The method of <FIG> describes step <NUM> as engaging at least one coupling mechanism. The step <NUM> may include engaging a snap-fit coupling mechanism, a friction-fit coupling mechanism, an adhesive coupling mechanism, or any other coupling mechanism suitable for the purposes described herein. Moreover, the various coupling mechanisms described may be used in any combination. Further, in embodiments utilizing an adhesive coupling mechanism, the adhesive may be applied to the housing <NUM> and/or to the cover <NUM> at any time prior to step <NUM>.

Although the method of <FIG> describes step <NUM> as occurring after steps <NUM>-<NUM>, step <NUM> may occur at any time during the manufacturing process, including being formed as part of the tip <NUM>. Further, while step <NUM> describes creating the aperture <NUM> in the tip <NUM>, this is not meant to limit the method, and step <NUM> may alternatively include creating the aperture <NUM> in a portion of the tip <NUM>, in the cover <NUM>, in a portion of the cover <NUM>, or in any combination thereof. Even further, more than one aperture <NUM> may be created.

<FIG> shows a method of manufacturing a distal shaft <NUM> of an FFR catheter for measuring a distal pressure measurement on a distal side of a stenosis according to another embodiment hereof. Steps <NUM>-<NUM> of <FIG> reference the partial cylinder cover <NUM> and the distal shaft <NUM> shown in <FIG>.

In step <NUM>, the cover <NUM> is positioned with the open portion <NUM> of the cover <NUM> over the open seat <NUM> of the housing <NUM>.

In step <NUM>, a sufficient force is applied to the cover <NUM> and/or the housing <NUM> towards each other such that the coupling mechanism is engaged and the cover <NUM> is coupled to the housing <NUM> of a distal shaft <NUM>.

In step <NUM>, the aperture <NUM> is created in the tip <NUM> extending from an outer surface of the tip <NUM> to an open seat <NUM> of a housing <NUM>.

The method of <FIG> describes step <NUM> as engaging the coupling mechanism. Step <NUM> may including engaging a friction-fit coupling mechanism, a snap-fit coupling mechanism, an adhesive coupling mechanism, or any other suitable coupling mechanism. Further, the various coupling mechanisms described may be used in any combination. If an adhesive coupling mechanism is utilized, the adhesive may be applied to the housing <NUM> and/or the cover <NUM> prior to step <NUM>.

Although the method of <FIG> describes step <NUM> as occurring after steps <NUM>-<NUM>, step <NUM> may occur at any suitable time during the manufacturing method, including being formed as part of the tip <NUM>.

Moreover while step <NUM> describes creating the aperture <NUM> in the tip <NUM>, this is not meant to limit the method, and step <NUM> may alternatively include creating the aperture <NUM> in a portion of the tip <NUM>, in the cover <NUM>, in a portion of the cover <NUM>, or in any combination thereof. Even further, more than one aperture <NUM> may be created.

While the methods of <FIG> are described with respect to specific embodiments of the invention described herein, this is not meant to limit the methods, and persons skilled in the art will understand the methods described herein may utilize a cover according to other embodiments.

Claim 1:
A distal shaft (<NUM>) for measuring a pressure distal (Pd) of a stenosis (<NUM>), the distal shaft (<NUM>) comprising:
a housing (<NUM>);
a pressure sensor (<NUM>) mounted in the housing (<NUM>);
a cover (<NUM>) coupled to the housing (<NUM>) and covering the pressure sensor (<NUM>);
a tip (<NUM>) coupled to a distal end (<NUM>) of the housing (<NUM>); and
an aperture (<NUM>) disposed through the tip (<NUM>) and/or the cover (<NUM>), the aperture (<NUM>) configured to allow blood flow to the pressure sensor (<NUM>); and
wherein the cover (<NUM>) is a separate piece than the housing (<NUM>) and is coupled thereto;
wherein the housing (<NUM>) includes a guidewire lumen (<NUM>); and
characterized in that
the housing (<NUM>) comprises a first material and the cover comprises a second material, wherein the second material is stiffer than the first material.