Patent Description:
The present disclosure pertains to medical devices, and methods for using medical devices. More particularly, the present disclosure pertains to methods for assessing fractional flow reserve.

A wide variety of intracorporeal medical devices have been developed for medical use, for example, intravascular use. Some of these devices include guidewires, catheters, and the like. These devices are manufactured by any one of a variety of different manufacturing methods and may be used according to any one of a variety of methods. Of the known medical devices and methods, each has certain advantages and disadvantages. There is an ongoing need to provide alternative medical devices as well as alternative methods for manufacturing and using medical devices.

<CIT> discloses devices, systems, and methods for visually depicting a vessel and evaluating treatment options are disclosed. The methods can include obtaining pressure measurements from first and second instruments positioned within a vessel of a patient while the second instrument is moved longitudinally through the vessel from a first position to a second position and the first instrument remains stationary within the vessel; and outputting a visual representation of the pressure measurements obtained by the first and second instruments on a display, the output visual representation including a graphical display of a pressure ratio of the obtained pressure measurements and at least a portion of a pressure waveform of the obtained pressure measurements identifying a diagnostic period utilized in calculating the pressure ratio.

This disclosure provides design, material, manufacturing methods, and use alternatives for medical devices. An example medical device includes a system for determining fractional flow reserve. The system comprises: a pressure sensing guidewire for measuring a first pressure; a second pressure sensing medical device for measuring a second pressure; a processor coupled to the pressure sensing guidewire and coupled to the second pressure sensing medical device; wherein the processor is designed to: generate a plot of the magnitude of the second pressure over time, identify one or more time intervals of the plot that have a slope less than zero, determine a mean of the second pressure, and calculate the ratio of the first pressure to the second pressure when (a) the second pressure is less than or equal to the mean of the second pressure and (b) during the one or more time intervals when the slope of the plot is less than zero.

Alternatively or additionally to any of the embodiments above, the pressure sensing guidewire includes an optical pressure sensor.

Alternatively or additionally to any of the embodiments above, the pressure sensing guidewire includes a tubular member having a proximal region with a first inner diameter and a distal region with a second inner diameter different from the first inner diameter.

Alternatively or additionally to any of the embodiments above, the second pressure sensing medical device includes a catheter with a pressure sensor.

Alternatively or additionally to any of the embodiments above, the first pressure, the second pressure, or both are wirelessly transmitted to the processor.

Alternatively or additionally to any of the embodiments above, the pressure sensing guidewire is designed to be disposed distal of an intravascular lesion.

Alternatively or additionally to any of the embodiments above, the second pressure sensing medical device is designed to be disposed proximal of an intravascular lesion.

Alternatively or additionally to any of the embodiments above, the processor is designed to calculate the ratio of the first pressure to the second pressure in the absence of a hyperemic agent.

Alternatively or additionally to any of the embodiments above, the processor is coupled to a display.

Alternatively or additionally to any of the embodiments above, the display is designed to display the plot.

A system for determining fractional flow reserve is disclosed. The system comprises: a pressure sensing guidewire for measuring a distal pressure at a location distal of a lesion; a pressure sensing catheter for measuring an aortic pressure; a processor coupled to the pressure sensing guidewire and coupled to the pressure sensing catheter; and wherein the processor is designed to: generate a plot of the magnitude of the aortic pressure over time, identify one or more time intervals of the plot that have a slope less than zero, determine a mean of the aortic pressure, and calculate the ratio of the distal pressure to the aortic pressure when (a) the aortic pressure is less than or equal to the mean of aortic pressure and (b) during the one or more time intervals when the slope of the plot is less than zero.

Alternatively or additionally to any of the embodiments above, the processor is designed to calculate the ratio of the distal pressure to the aortic pressure in the absence of a hyperemic agent.

Alternatively or additionally to any of the embodiments above, the processor is designed to scale the mean aortic pressure by a scaling factor in the range of <NUM> to <NUM>.

Alternatively or additionally to any of the embodiments above, the processor is designed to reject time intervals when the aortic pressure is less than a pressure lower bound.

A method for determining fractional flow reserve is disclosed. The method comprises: disposing a pressure sensing guidewire distal of an intravascular lesion; measuring a distal pressure with the pressure sensing guidewire; disposing a pressure sensing catheter in a vascular region; measuring an aortic pressure with the pressure sensing catheter; wherein a processor is coupled to the pressure sensing guidewire and coupled to the pressure sensing catheter; wherein the processor is designed to: generate a plot of the magnitude of the aortic pressure over time, identify one or more time intervals of the plot that have a slope less than zero, and determine a mean of the aortic pressure; and calculating a ratio of the distal pressure to the aortic pressure when (a) the aortic pressure is less than or equal to the mean of the aortic pressure (b) during the one or more time intervals when the slope of the plot is less than zero.

Alternatively or additionally to any of the embodiments above, measuring a distal pressure with the pressure sensing guidewire includes measuring the distal pressure in the absence of a hyperemic agent, wherein measuring an aortic pressure with the pressure sensing catheter includes measuring the aortic pressure in the absence of a hyperemic agent, or both.

Alternatively or additionally to any of the embodiments above, calculating a ratio of the distal pressure to the aortic pressure includes calculating the ratio of the distal pressure to the aortic pressure in the absence of a hyperemic agent.

During some medical interventions, it may be desirable to measure and/or monitor the blood pressure within a blood vessel. For example, some medical devices may include pressure sensors that allow a clinician to monitor blood pressure. Such devices may be useful in determining fractional flow reserve (FFR), which may be understood as a ratio of the pressure after, or distal, of a stenosis (e.g., the distal pressure, Pd) relative to the pressure before the stenosis and/or the aortic pressure (e.g., the aortic pressure, Pa). In other words, FFR may be understood as Pd/Pa.

An example system <NUM> for assessing/determining FFR is schematically represented in <FIG>. The system <NUM> may include a first pressure sensing medical device <NUM>. In at least some instances, the first pressure sensing medical device <NUM> may take the form of a pressure sensing guidewire <NUM>. Some additional detail regarding the form of the guidewire <NUM>, provided as an example, is disclosed herein. In other instances, the first pressure sensing medical device <NUM> may be a catheter or other type of pressure sensing medical device. The pressure sensing guidewire <NUM> may be utilized to measure blood pressure distal of an intravascular stenosis, e.g., the distal pressure Pd. The first pressure sensing medical device <NUM> may be coupled to a linking device <NUM>. In some instances, this may include directly attaching the first pressure sensing medical device <NUM> to the linking device <NUM>. In other instances, another structure such as a connector cable (not shown) may be used to couple the first pressure sensing medical device <NUM> to the linking device <NUM>. When the first pressure sensing medical device <NUM> is coupled to the linking device <NUM>, a first pressure data <NUM> may be communicated between the first pressure sensing medical device <NUM> and the linking device <NUM>. It is noted that in <FIG>, a line is drawn between the first pressure sensing medical device <NUM> and the linking device <NUM> to represent the coupling of the first pressure sensing medical device <NUM> and the linking device <NUM>. In addition the line between the first pressure sensing medical device <NUM> and the linking device <NUM> is labeled with reference number <NUM> in order to represent the transmission of the first pressure data <NUM> (and/or the first pressure data <NUM> itself). In at least some instances, the first pressure data <NUM> is the distal pressure Pd.

The system <NUM> also includes a second pressure sensing medical device <NUM>. In at least some instances, the second pressure sensing medical device <NUM> may take the form of a pressure sensing catheter. However, other devices are contemplated including pressure sensing guidewires or other devices. The second pressure sensing medical device <NUM> may be utilized to measure blood pressure proximal of an intravascular stenosis and/or the aortic pressure, e.g., the aortic pressure Pa. The second pressure sensing medical device <NUM> may also be coupled to the linking device <NUM> and may communicate a second pressure data <NUM> between the second pressure sensing medical device <NUM> and the linking device <NUM>. It is noted that in <FIG>, a line is drawn between the second pressure sensing medical device <NUM> and the linking device <NUM> to represent the coupling of the second pressure sensing medical device <NUM> and the linking device <NUM>. In addition the line between the second pressure sensing medical device <NUM> and the linking device <NUM> is labeled with reference number <NUM> in order to represent the transmission of the second pressure data <NUM> (and/or the second pressure data <NUM> itself). In at least some instances, the second pressure data <NUM> is the aortic pressure Pa.

In some instances, the linking device <NUM> may communicate with a hemodynamic system <NUM> (e.g., a hemodynamic display system <NUM>). When doing so, data representative of the distal pressure Pd (represented by reference number <NUM>) may be communicated to the hemodynamic system <NUM> and data representative of the aortic pressure Pa (represented by reference number <NUM>) may be communicated to the hemodynamic system <NUM>. In some instances, both connections between the linking device <NUM> and the hemodynamic system <NUM> (e.g., for communicating Pd and Pa) may be wired connections. In other instances, one or both of the connections may be wireless connections. In still other instances, both Pd and Pa may be communicated along a single wired connection.

In some instances, the linking device <NUM> may also communicate with a processing and/or display system <NUM>. When doing so, data representative of the distal pressure Pd and data representative of the aortic pressure Pa (both the distal pressure Pd and the aortic pressure Pa data are represented by reference number <NUM> in <FIG>) may be communicated to the processing and/or display system <NUM>. In at least some instances, Pd and Pa may be communicated between the linking device <NUM> and the processing and/or display system <NUM> using a wireless connection. In other instances, one or both of Pd and Pa may be communicated between the linking device <NUM> and the processing and/or display system <NUM> with a wired connection.

The processing and/or display system <NUM> may include a processor <NUM>. The processor <NUM> may be an integrated component of the processing and/or display system <NUM> (e.g., the processor <NUM> may be disposed within the same housing as the processing and/or display system <NUM>) or the processor <NUM> may be separate component of the processing and/or display system <NUM> and coupled therewith. The processor <NUM> may be coupled to the first pressure sensing medical device <NUM> and coupled to the second pressure sensing medical device <NUM> such that pressure measurements (e.g., Pd and Pa) may be received by the processor <NUM> from the first pressure sensing medical device <NUM> and the second pressure sensing medical device <NUM>. The processor <NUM> may be designed to and/or otherwise be capable of performing a number of calculations, executing instructions, etc. For example, the processor may be designed to calculate/determine the mean distal pressure Pd (e.g., as measured by the first pressure sensing medical device <NUM> over one or more cardiac cycles), calculate/determine the mean aortic pressure Pa (e.g., as measured by the second pressure sensing medical device <NUM> over one or more cardiac cycles), plot the distal pressure Pd and/or the aortic pressure Pa over time, calculate/determine the slope of the plot of the distal pressure Pd and/or the slope of the plot of the aortic pressure Pa (e.g., at various points along the plot), or the like. A display <NUM> may be coupled to or otherwise integrated with the processing and/or display system <NUM>. The display <NUM> may display various data received from first pressure sensing medical device <NUM> and the second pressure sensing medical device <NUM>, plots of the pressure data as generated by the processor <NUM>, etc..

When determining FFR, it may be desirable to measure a change or drop in pressure across a stenosis while under a maximum flow condition (e.g., hyperemia). Thus, a number of interventions that are performed to assess FFR include the administration of hyperemic agents such as adenosine to cause maximum flow conditions. For a number of reasons (e.g., patient comfort, extended procedure time, technical challenges associated with mixing adenosine for intravascular administration, cost, etc.), it may be desirable to reduce the use of hyperemic agents. Pressure measurements performed under a resting condition conduction are typically referred as resting indices. An example of such a measurement is resting Pd/Pa in which the ratio is computed with data from the whole cardiac cycle. Disclosed herein are methods for assessing/determining FFR that can be performed in the absence of hyperemic agents including adenosine.

The maximum coronary flow occurs during the diastolic period of the cardiac cycle. Therefore, measurements of Pd and Pa during a diastolic period may provide a ratio closer to FFR (e.g., a better approximation of FFR) than that obtained from the whole cardiac cycle. In addition to resting Pd/Pa, some methods for assessing FFR may include computing Pd and Pa during time windows from the diastolic period. For example, some interventions such as instantaneous wave-free ratio and/or iFR™ may attempt to measure FFR during diastole. Such methods may require accurate measurement of waveform timing and/or synchronization with an ECG, which may complicate the process for assessing/determining FFR. Disclosed herein are methods for assessing/determining FFR by monitoring Pd and Pa during specific windows during the diastolic period of the cardiac cycle. The methods for assessing/determining FFR disclosed herein are relatively straightforward to implement such that FFR can be assessed/determined in a timely manner that enhances the comfort for the patient and that does not require unnecessary additional processes and/or synchronization.

<FIG> graphically depicts pressure measurements over a number of cardiac cycles (e.g., one full cycle is depicted plus a portion of another cardiac cycle). In this example, a graphical depiction of Pd (e.g., as measured by the first pressure sensing medical device <NUM>) and a graphical depiction of Pa (e.g., as measured by the second pressure sensing medical device <NUM>) are shown over time. Also shown is the mean aortic pressure <NUM>.

In order to assess/determine FFR, the processor <NUM> is utilized to perform a number of tasks including:.

According to the invention, regions of the cardiac cycle are identified where:.

In another example, regions of the cardiac cycle are identified where:.

The mean aortic pressure <NUM> may be determined for each individual cardiac cycle or across a number of cardiac cycles. Time windows or regions that meet these criteria are believed to be during high flow periods (e.g., during the diastolic period) and are believed to be suitable for use in assessing/determining FFR. Thus, the system <NUM> can be utilized to assess/determine/calculate FFR during these periods in the absence of hyperemic agents and/or without the need for unnecessary additional processes and/or synchronization. In the graph shown in <FIG>, three time regions 96a, 96b, 96c are defined that meet these criteria. It can be appreciated that in other plots/graphs, fewer or more time regions may be identified. The processor <NUM> is utilized to assess/determine/calculate FFR during these time regions 96a, 96b, 96c.

<FIG> illustrates a portion of the first pressure sensing medical device <NUM> that may be part of the system <NUM>. In this example, the first pressure sensing medical device <NUM> is a blood pressure sensing guidewire <NUM>. However, this is not intended to be limiting as other medical devices are contemplated including, for example, catheters, shafts, leads, wires, or the like. The guidewire <NUM> may include a shaft or tubular member <NUM>. The tubular member <NUM> may include a proximal region <NUM> and a distal region <NUM>. The materials for the proximal region <NUM> and the distal region <NUM> may vary and may include those materials disclosed herein. For example, the distal region <NUM> may include a nickel-cobalt-chromium-molybdenum alloy (e.g., MP35-N). The proximal region <NUM> may be made from the same material as the distal region <NUM> or a different material such as stainless steel. These are just examples. Other materials are contemplated.

In some embodiments, the proximal region <NUM> and the distal region <NUM> are formed from the same monolith of material. In other words, the proximal region <NUM> and the distal region <NUM> are portions of the same tube defining the tubular member <NUM>. In other embodiments, the proximal region <NUM> and the distal region <NUM> are separate tubular members that are joined together. For example, a section of the outer surface of the portions <NUM>/<NUM> may be removed and a sleeve <NUM> may be disposed over the removed sections to join the regions <NUM>/<NUM>. Alternatively, the sleeve <NUM> may be simply disposed over the regions <NUM>/<NUM>. Other bonds may also be used including welds, thermal bonds, adhesive bonds, or the like. If utilized, the sleeve <NUM> used to join the proximal region <NUM> with the distal region <NUM> may include a material that desirably bonds with both the proximal region <NUM> and the distal region <NUM>. For example, the sleeve <NUM> may include a nickel-chromium-molybdenum alloy (e.g., INCONEL).

A plurality of slots <NUM> may be formed in the tubular member <NUM>. In at least some embodiments, the slots <NUM> are formed in the distal region <NUM>. In at least some embodiments, the proximal region <NUM> lacks slots <NUM>. However, the proximal region <NUM> may include slots <NUM>. The slots <NUM> may be desirable for a number of reasons. For example, the slots <NUM> may provide a desirable level of flexibility to the tubular member <NUM> (e.g., along the distal region <NUM>) while also allowing suitable transmission of torque. The slots <NUM> may be arranged/distributed along the distal region <NUM> in a suitable manner. For example, the slots <NUM> may be arranged as opposing pairs of slots <NUM> that are distributed along the length of the distal region <NUM>. In some embodiments, adjacent pairs of slots <NUM> may have a substantially constant spacing relative to one another. Alternatively, the spacing between adjacent pairs may vary. For example, more distal regions of the distal region <NUM> may have a decreased spacing (and/or increased slot density), which may provide increased flexibility. In other embodiments, more distal regions of the distal region <NUM> may have an increased spacing (and/or decreased slot density). These are just examples. Other arrangements are contemplated.

A pressure sensor <NUM> may be disposed within the tubular member <NUM> (e.g., within a lumen of tubular member <NUM>). While the pressure sensor <NUM> is shown schematically in <FIG>, it can be appreciated that the structural form and/or type of the pressure sensor <NUM> may vary. For example, the pressure sensor <NUM> may include a semiconductor (e.g., silicon wafer) pressure sensor, piezoelectric pressure sensor, a fiber optic or optical pressure sensor, a Fabry-Perot type pressure sensor, an ultrasound transducer and/or ultrasound pressure sensor, a magnetic pressure sensor, a solid-state pressure sensor, or the like, or any other suitable pressure sensor.

As indicated above, the pressure sensor <NUM> may include an optical pressure sensor. In at least some of these embodiments, an optical fiber or fiber optic cable <NUM> (e.g., a multimode fiber optic) may be attached to the pressure sensor <NUM> and may extend proximally therefrom. The optical fiber <NUM> may include a central core <NUM> and an outer cladding <NUM>. In some instances, a sealing member (not shown) may attach the optical fiber <NUM> to the tubular member <NUM>. Such an attachment member may be circumferentially disposed about and attached to the optical fiber <NUM> and may be secured to the inner surface of the tubular member <NUM> (e.g., the distal region <NUM>). In addition, a centering member <NUM> may also be bonded to the optical fiber <NUM>. In at least some embodiments, the centering member <NUM> is proximally spaced from the pressure sensor <NUM>. Other arrangements are contemplated. The centering member <NUM> may help reduce forces that may be exposed to the pressure sensor <NUM> during navigation of guidewire and/or during use.

In at least some embodiments, the distal region <NUM> may include a region with a thinned wall and/or an increased inner diameter that defines a sensor housing region <NUM>. In general, the sensor housing region <NUM> is the region of distal region <NUM> that ultimately "houses" the pressure sensor <NUM>. By virtue of having a portion of the inner wall of the tubular member <NUM> being removed at the sensor housing region <NUM>, additional space may be created or otherwise defined that can accommodate the sensor <NUM>. The sensor housing region <NUM> may include one or more openings such as one or more distal porthole openings <NUM> that provide fluid access to the pressure sensor <NUM>.

A tip member <NUM> may be coupled to the distal region <NUM>. The tip member <NUM> may include a core member <NUM> and a spring or coil member <NUM>. A distal tip <NUM> may be attached to the core member <NUM> and/or the spring <NUM>. In at least some embodiments, the distal tip <NUM> may take the form of a solder ball tip. The tip member <NUM> may be joined to the distal region <NUM> of the tubular member <NUM> with a bonding member <NUM> such as a weld.

The tubular member <NUM> may include an outer coating <NUM>. In some embodiments, the coating <NUM> may extend along substantially the full length of the tubular member <NUM>. In other embodiments, one or more discrete sections of the tubular member <NUM> may include the coating <NUM>. The coating <NUM> may be a hydrophobic coating, a hydrophilic coating, or the like. The tubular member <NUM> may also include an inner coating <NUM> (e.g., a hydrophobic coating, a hydrophilic coating, or the like) disposed along an inner surface thereof. For example, the hydrophilic coating <NUM> may be disposed along the inner surface of the housing region <NUM>. In some of these and in other instances, the core member <NUM> may include a coating (e.g., a hydrophilic coating). For example, a proximal end region and/or a proximal end of the core member <NUM> may include the coating. In some of these and in other instances, the pressure sensor <NUM> may also include a coating (e.g., a hydrophilic coating).

The materials that can be used for the various components of the system <NUM> and/or the guidewire <NUM> may include those commonly associated with medical devices. For simplicity purposes, the following discussion makes reference to the tubular member <NUM> and other components of the guidewire <NUM>. However, this is not intended to limit the devices and methods described herein, as the discussion may be applied to other tubular members and/or components of tubular members or devices disclosed herein.

The tubular member <NUM> and/or other components of the guidewire <NUM> may be made from a metal, metal alloy, polymer (some examples of which are disclosed below), a metal-polymer composite, ceramics, combinations thereof, and the like, or other suitable material. Some examples of suitable polymers may include polytetrafluoroethylene (PTFE), ethylene tetrafluoroethylene (ETFE), fluorinated ethylene propylene (FEP), polyoxymethylene (POM, for example, DELRIN® available from DuPont), polyether block ester, polyurethane (for example, Polyurethane 85A), polypropylene (PP), polyvinylchloride (PVC), polyether-ester (for example, ARNITEL® available from DSM Engineering Plastics), ether or ester based copolymers (for example, butylene/poly(alkylene ether) phthalate and/or other polyester elastomers such as HYTREL® available from DuPont), polyamide (for example, DURETHAN® available from Bayer or CRISTAMID® available from Elf Atochem), elastomeric polyamides, block polyamide/ethers, polyether block amide (PEBA, for example available under the trade name PEBAX®), ethylene vinyl acetate copolymers (EVA), silicones, polyethylene (PE), Marlex high-density polyethylene, Marlex low-density polyethylene, linear low density polyethylene (for example REXELL®), polyester, polybutylene terephthalate (PBT), polyethylene terephthalate (PET), polytrimethylene terephthalate, polyethylene naphthalate (PEN), polyetheretherketone (PEEK), polyimide (PI), polyetherimide (PEI), polyphenylene sulfide (PPS), polyphenylene oxide (PPO), poly paraphenylene terephthalamide (for example, KEVLAR®), polysulfone, nylon, nylon-<NUM> (such as GRILAMID® available from EMS American Grilon), perfluoro(propyl vinyl ether) (PFA), ethylene vinyl alcohol, polyolefin, polystyrene, epoxy, polyvinylidene chloride (PVdC), poly(styreneb-isobutylene-b-styrene) (for example, SIBS and/or SIBS 50A), polycarbonates, ionomers, biocompatible polymers, other suitable materials, or mixtures, combinations, copolymers thereof, polymer/metal composites, and the like. In some embodiments the sheath can be blended with a liquid crystal polymer (LCP). For example, the mixture can contain up to about <NUM> percent LCP.

Some examples of suitable metals and metal alloys include stainless steel, such as 304V, <NUM>, and 316LV stainless steel; mild steel; nickel-titanium alloy such as linear-elastic and/or super-elastic nitinol; other nickel alloys such as nickel-chromium-molybdenum alloys (e.g., UNS: N06625 such as INCONEL® <NUM>, UNS: N06022 such as HASTELLOY® C-<NUM>®, UNS: N10276 such as HASTELLOY® C276®, other HASTELLOY® alloys, and the like), nickel-copper alloys (e.g., UNS: N04400 such as MONEL® <NUM>, NICKELVAC® <NUM>, NICORROS® <NUM>, and the like), nickel-cobalt-chromium-molybdenum alloys (e.g., UNS: R30035 such as MP35-N® and the like), nickel-molybdenum alloys (e.g., UNS: N10665 such as HASTELLOY® ALLOY B2®), other nickel-chromium alloys, other nickel-molybdenum alloys, other nickel-cobalt alloys, other nickel-iron alloys, other nickel-copper alloys, other nickeltungsten or tungsten alloys, and the like; cobalt-chromium alloys; cobalt-chromium-molybdenum alloys (e.g., UNS: R30003 such as ELGILOY®, PHYNOX®, and the like); platinum enriched stainless steel; titanium; combinations thereof; and the like; or any other suitable material.

In at least some embodiments, portions or all of guidewire <NUM> may also be doped with, made of, or otherwise include a radiopaque material. Radiopaque materials are understood to be materials capable of producing a relatively bright image on a fluoroscopy screen or another imaging technique during a medical procedure. This relatively bright image aids the user of the guidewire <NUM> in determining its location. Some examples of radiopaque materials can include, but are not limited to, gold, platinum, palladium, tantalum, tungsten alloy, polymer material loaded with a radiopaque filler, and the like. Additionally, other radiopaque marker bands and/or coils may also be incorporated into the design of the guidewire <NUM> to achieve the same result.

In some embodiments, a degree of Magnetic Resonance Imaging (MRI) compatibility is imparted into the guidewire <NUM>. For example, the guidewire <NUM>, or portions thereof, may be made of a material that does not substantially distort the image and create substantial artifacts (e.g., gaps in the image). Certain ferromagnetic materials, for example, may not be suitable because they may create artifacts in an MRI image. The guidewire <NUM>, or portions thereof, may also be made from a material that the MRI machine can image. Some materials that exhibit these characteristics include, for example, tungsten, cobalt-chromium-molybdenum alloys (e.g., UNS: R30003 such as ELGILOY®, PHYNOX®, and the like), nickel-cobalt-chromium-molybdenum alloys (e.g., UNS: R30035 such as MP35-N® and the like), nitinol, and the like, and others.

Claim 1:
A system (<NUM>) for determining fractional flow reserve, the system comprising:
a first pressure sensing medical device (<NUM>) for measuring a first pressure;
a second pressure sensing medical device (<NUM>) for measuring a second pressure;
a processor (<NUM>) coupled to the first pressure sensing medical device (<NUM>) and coupled to the second pressure sensing medical device (<NUM>); and
wherein the processor (<NUM>) is configured to:
generate a plot of the magnitude of the second pressure over time,
identify one or more time intervals (96a, 96b, 96c) of the plot that have a slope less than zero,
determine a mean of the second pressure, and
calculate the ratio of the first pressure to the second pressure when (a) the second pressure is less than or equal to the mean of the second pressure and (b) during the one or more time intervals (96a, 96b, 96c) when the slope of the plot is less than zero.