Vascular assessment

Abstract

To provide devices, systems, and methods for assessing anatomical structures of patients, such as a constriction or narrowing at a location of interest in a blood vessel.SOLUTION: One method for assessing a vessel can include obtaining a set of first location pressure measurements at a first location in the vessel over a first time period, and a set of second location pressure measurements at a second location in the vessel over the first time period. This method can further include identifying a first leading characteristic associated with one or more pressure measurements in the set of first location pressure measurements, a second leading characteristic associated with one or more pressure measurements in the set of second location pressure measurements, a first trailing characteristic associated with one or more pressure measurements in the set of first location pressure measurements, and a second trailing characteristic associated with one or more pressure measurements in the set of second location pressure measurements. In addition, this method can include calculating a pressure ratio using pressure measurements between the identified characteristics.SELECTED DRAWING: Figure 3B

Description

[Technical field]

[0001] Related Applications This application claims the benefit of U.S. Provisional Patent Application No. 62 / 660,521, filed April 20, 2018, the contents of which are incorporated herein by reference.

[0002] The present disclosure relates generally to the field of medical technology, and more specifically to devices, systems and methods for assessing a patient's anatomy, such as a constriction or stenosis at a location of interest in a blood vessel. [Background technology]

[0003] To better understand the severity of certain conditions in a patient's anatomy, physiological data can be collected and used to guide treatment decisions. One example of such a condition is the constriction or narrowing of a blood vessel, sometimes referred to as stenosis. By measuring the severity of the stenosis, appropriate treatment options can be determined.

[0004] One technique for assessing the extent to which a stenosis impedes flow through a blood vessel is called fractional flow reserve measurement (FFR). To calculate the FFR of a particular blood vessel, two blood pressure readings are taken, one distal to the stenosis (e.g., downstream of the stenosis) and one proximal or aortic side of the stenosis (e.g., upstream of the stenosis, toward the aorta). FFR is defined as the ratio of the maximum blood flow of the stenosed artery distal to the stenosis to the normal maximum blood flow, and is typically calculated based on a measured pressure gradient from distal to proximal pressure. The pressure gradient across the stenosis can serve as an indicator of the severity of the stenosis. The more restrictive the stenosis, the greater the pressure drop and the lower the resulting FFR. FFR measurements can be a useful diagnostic tool. A physician may, for example, decide to perform an interventional procedure (e.g., angioplasty or stenting) when the FFR for a given stenosis falls below a clinical threshold (e.g., 0.8), and may decide to refrain from such treatment for a given stenosis if the FFR exceeds the clinical threshold (e.g., 0.8). Thus, the FFR measurement may be a decision point to guide treatment.

[0005] However, accurate assessment of pressure drop across a stenosis generally requires that coronary resistance be stable and minimal. In traditional FFR, this has typically been achieved by inducing maximal hyperemia in the vessels through administration of a pharmacological hyperemic agent, such as adenosine. It would be desirable to create an approximation of FFR under normal flow conditions without the need to administer drugs, as this would reduce patient side effects as well as the cost and time associated with diagnostic evaluation.

[0006] Techniques have been developed recently to approximate FFR when coronary resistance is naturally minimized and therefore pharmacological agents are not required. These techniques focus on identifying the diastolic phase of the cardiac cycle and taking pressure measurements during defined subperiods of diastole where resistance has been empirically shown to be low. However, to identify diastole, these techniques rely on first identifying the dicrotic notch in the pressure measurement. The dicrotic notch represents the closure of the aortic valve at the beginning of ventricular diastole and appears in the pressure waveform as a relatively slight upward deflection in the descending portion of the pressure waveform. However, depending on the particular patient, it may be difficult to detect the dicrotic notch and in some cases there may be no discernible dicrotic notch. Because these FFR approximation techniques define the pressure measurement period relative to the dicrotic notch, failure to accurately identify the dicrotic notch may lead to the use of pressure measurements taken when vascular resistance is significant, thus resulting in inaccurate approximation of the FFR. This may reduce the value of FFR approximation in guiding therapy. Summary of the Invention

[0007] Exemplary embodiments for evaluating a patient's blood vessels or other relevant anatomical structures (e.g., valves) are described herein. Various embodiments described herein may be useful in providing an approximation of fractional flow reserve (FFR) that may serve as a reliable decision point for guiding treatment decisions, as the approximation provided may be comparable to conventional FFR. Furthermore, certain embodiments may provide this approximation of FFR under normal flow conditions, for example, without inducing hyperemia (e.g., without administering hyperemic medication) and / or without the need to identify the dicrotic notch. The embodiments disclosed herein may identify characteristics other than the dicrotic notch that are associated with pressure measurements taken when not in hyperemia, and use these identified characteristics to select pressure measurements taken when vascular resistance is naturally at a minimum. Thus, such embodiments may reduce patient side effects, as well as costs and time, associated with inducing hyperemia, while providing a more consistent and accurate approximation of FFR by eliminating the need to identify the dicrotic notch.

[0008] An exemplary embodiment includes a method for evaluating a blood vessel. In this exemplary embodiment, the method includes obtaining a set of first location pressure measurements at a first location in the blood vessel over a first period of time, and a set of second location pressure measurements at a second location in the blood vessel over the first period of time. The second location is different from the first location. For example, the first location may be one of distal to the location of interest and proximal to the location of interest, while the second location may be the other of distal to the location of interest and proximal to the location of interest. The set of first location pressure measurements and the set of second location pressure measurements may be obtained when not hyperemic (i.e., non-hyperemic state).

[0009] This method embodiment further includes identifying a first pre-characteristic associated with one or more pressure measurements in the set of pressure measurements at the first location, and a second pre-characteristic associated with one or more pressure measurements in the set of pressure measurements at the second location.

[0010] The embodiment of the method also includes identifying a first posterior characteristic associated with one or more pressure measurements in the set of pressure measurements at the first location and a second posterior characteristic associated with one or more pressure measurements in the set of pressure measurements at the second location. The identified first posterior characteristic follows the identified first posterior characteristic in the first time period and the identified second posterior characteristic follows the identified second posterior characteristic in the first time period. Further, at least one of the identified first posterior characteristic, the identified second posterior characteristic, the identified first posterior characteristic, and the identified second posterior characteristic are associated with pressure measurements in the respective sets of pressure measurements at the first location and the second location that are obtained without considering any dicrotic notch that may be present in the respective sets of pressure measurements at the first location and the second location.

[0011] Further embodiments of the method include calculating a numerical value based on i) pressure measurements in the set of pressure measurements at a first location between the identified first pre-characteristic and the identified first post-characteristic, and ii) pressure measurements in the set of pressure measurements at a second location between the identified second pre-characteristic and the identified second post-characteristic. For example, the method may include calculating a pressure ratio using i) pressure measurements in the set of pressure measurements at a first location between the identified first pre-characteristic and the identified first post-characteristic, and ii) pressure measurements in the set of pressure measurements at a second location between the identified second pre-characteristic and the identified second post-characteristic. The method may further include providing a numerical value as an assessment of the restriction in the vessel.

[0012] Another exemplary embodiment includes a non-transitory computer-readable storage article having computer-executable instructions stored thereon. In this embodiment, the computer-executable instructions cause at least one programmable processor to receive a set of first location pressure measurements taken at a first location in a blood vessel over a first time period, and a set of second location pressure measurements taken at a second location in the blood vessel over the first time period, the second location being different from the first location, and the set of first location pressure measurements and the set of second location pressure measurements taken when not hyperemic (i.e., in a non-hyperemic state).

[0013] In an embodiment of this article, the computer-executable instructions further cause the at least one programmable processor to identify a first pre-characteristic associated with one or more pressure measurements in the set of pressure measurements at the first location, and a second pre-characteristic associated with one or more pressure measurements in the set of pressure measurements at the second location.

[0014] In an embodiment of this article, the computer-executable instructions also cause the at least one programmable processor to identify a first posterior characteristic associated with one or more pressure measurements in the set of pressure measurements at the first location and a second posterior characteristic associated with one or more pressure measurements in the set of pressure measurements at the second location, the first posterior characteristic following the first posterior characteristic in a first time period and the second posterior characteristic following the second posterior characteristic in the first time period. Further, at least one of the identified first posterior characteristic, the identified second posterior characteristic, the identified first posterior characteristic, and the identified second posterior characteristic are associated with pressure measurements in the respective sets of pressure measurements at the first location and the second location that are obtained without considering any dicrotic notch that may be present in the respective sets of pressure measurements at the first location and the second location.

[0015] In an embodiment of this article, the computer-executable instructions additionally cause the at least one programmable processor to calculate a pressure ratio using i) pressure measurements in a set of pressure measurements at a first location between the first pre-characteristic and the first post-characteristic, and ii) pressure measurements in a set of pressure measurements at a second location between the second pre-characteristic and the second post-characteristic.

[0016] In these exemplary embodiments above, the identified characteristic may be any one or more of a variety of characteristic types. For example, the identified first pre-characteristic, the identified second pre-characteristic, the identified first post-characteristic and / or the identified second post-characteristic may be a characteristic type selected from a group of characteristic types consisting of: maximum pressure reading, minimum pressure reading, maximum decreasing pressure reading rate of change, and maximum increasing pressure reading rate of change. In some cases, all of the identified characteristics may be the same characteristic type, while in other cases, two or more different characteristic types may be identified.

[0017] The details of one or more examples are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will become apparent from the description and drawings. [Brief description of the drawings]

[0018] The following drawings illustrate certain embodiments of the present invention and therefore do not limit the scope of the invention. The drawings are intended to be used in conjunction with the explanations in the following description. Embodiments of the present invention are hereinafter described in conjunction with the accompanying drawings, in which like numerals indicate like elements.

[0019] [Figure 1] 1A and 1B are perspective views of an exemplary embodiment of a sensor delivery device. [Diagram 2] 2 is a diagram of an exemplary embodiment of a system for assessing the severity of a restriction at a location of interest in a blood vessel using the sensor delivery device of FIG. 1. [Figure 3A]3A illustrates a graphical representation of pressure measurements that may be used to calculate a numerical value such as a pressure ratio, according to an exemplary embodiment. FIG. 3A illustrates an exemplary embodiment in which a characteristic type of the maximum pressure measurement is identified. [Figure 3B] 3A-3C show graphical representations of pressure measurements that may be used to calculate numerical values ​​such as pressure ratios, according to an exemplary embodiment. FIG. 3B shows an exemplary embodiment in which a characteristic type of the maximum pressure measurement is identified, and FIG. 3B shows a particular aspect of this embodiment in which an independent characteristic identification is used. [Figure 4] 1 is a graphical representation of pressure measurements taken over several cycles that may be used to calculate values ​​such as pressure ratios, according to another illustrative embodiment. [Diagram 5] 5 is a graphical representation of pressure measurements that may be used to calculate a numerical value such as a pressure ratio, according to a further exemplary embodiment. In particular, FIG. 5 illustrates an exemplary embodiment in which a characteristic type of the minimum pressure measurement is identified. [Figure 6] 6 is a graphical representation of pressure measurements that may be used to calculate numerical values ​​such as pressure ratios, according to additional exemplary embodiments. In particular, FIG. 6 illustrates an exemplary embodiment in which a characteristic type of maximum decreasing pressure measurement rate of change is identified. [Figure 7] 7 is a graphical representation of pressure measurements that may be used to calculate a numerical value such as a pressure ratio, according to another exemplary embodiment. In particular, FIG. 7 illustrates an exemplary embodiment in which a characteristic type of maximum incremental pressure measurement rate of change is identified. [Figure 8] 8 is a graphical representation of pressure measurements that may be used to calculate numerical values ​​such as pressure ratios, according to further exemplary embodiments. In particular, FIG. 8 illustrates an exemplary embodiment in which a threshold decreasing pressure measurement rate of change characteristic type is identified. [Figure 9] FIG. 1 is a flow diagram of an exemplary embodiment of a method for evaluating a blood vessel, for example to assess the severity of a restriction at a location of interest within the vessel, without administering a hyperemic agent. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] The following detailed description is exemplary in nature and provides several illustrative diagrams and examples. Those skilled in the art will recognize that many of the mentioned examples have various suitable alternatives that should be considered within the scope of the present disclosure.

[0021] FIG. 1 illustrates a perspective view of an exemplary embodiment of a sensor delivery device 10 that may be used to collect one or more physiological parameters at a location of interest. The sensor delivery device 10 includes a distal sleeve 20 having a guidewire lumen 22 for slidably receiving a medical guidewire 30. A sensor 40 is coupled to the distal sleeve 20, the sensor 40 being configured to sense a physiological parameter of the patient and generate a signal representative of the physiological parameter (e.g., pressure). Thus, the distal sleeve 20, and thus the sensor 40, may be positioned within the patient (e.g., within the patient's anatomy, such as within a vein, artery, or other blood vessel, or even across a heart valve) by sliding the distal sleeve 20 over the medical guidewire 30 to a desired location. In some cases, such as the examples shown herein, the device 10 is deployed using a guide catheter 32. The guide catheter 32 may be placed within a blood vessel 34, which may be, for example, a coronary artery of the patient. The device 10 and the guidewire 30 may then be manipulated within the guide catheter 32. For example, the sensor 40 may be positioned within the blood vessel 34 distal to a location of interest within the blood vessel 34 and used to measure pressure therein during the cardiac cycle.

[0022] The sensor delivery device 10 of FIG. 1 also includes a proximal portion 50. As shown herein, the proximal portion 50 may be coupled to the distal sleeve 20. The proximal portion 50 includes a communication channel 60 for communicating signals from the sensor 40 to a location outside the patient (e.g., a processor, display, computer, monitor, or another medical device). The communication channel 60 may, in certain embodiments, include a fiber optic communication channel, such as when the sensor 40 is a fiber optic pressure sensor. Alternatively, the communication channel 60 may comprise a conductive medium, such as one or more conductive wires. Of course, many other forms of communication media are suitable for transmitting signals generated by the sensor 40 to a location outside the patient.

[0023] The proximal portion 50 may be adapted to assist an operator (e.g., a physician or other medical staff) in positioning the distal sleeve 20 and sensor 40 within the patient's anatomical (e.g., vascular) structure. This is typically accomplished by the operator first inserting the guidewire 30 into the patient's vasculature and advancing it past the area of ​​interest. The sensor delivery device 10 is then deployed by "threading" the distal sleeve 20 onto the guidewire 30 so that the lumen 22 slides over the guidewire 30, and advancing the distal sleeve 20 (and associated sensor 40) by moving (e.g., pushing and / or pulling) the proximal portion 50 until the sensor 40 is placed in the desired location relative to the location of interest in the blood vessel 34.

[0024] One diagnostic application for which sensor delivery device 10 may be suitable is the approximation of fractional flow reserve (FFR) in a blood vessel 34, or other suitable anatomical structure, such as a valve. In this application, device 10 may be deployed at one or more locations of interest in blood vessel 34, and sensor 40 may be configured to measure pressure at the one or more locations of interest. In one example, sensor 40 measures distal pressure P at a location downstream of a location of interest having a restriction (e.g., a stenosis) in blood vessel 34. dIn a further embodiment, the sensor 40 may then be positioned to measure the aortic pressure P at a location upstream of a location of interest having a restriction (e.g., a stenosis) in the blood vessel 34. a As shown in FIG. 1, the use of the terms "downstream" and "upstream" is with respect to the normal direction of blood flow D.

[0025] In some embodiments, device 10 can include a second sensor spaced apart from sensor 40 to span the stenosis. In other embodiments, a second pressure sensor separate from distal sleeve 20 and proximal portion 50 can be used. For example, in one embodiment, the second sensor is separate from device 10 and measures aortic pressure P at a location upstream of a location of interest having a restriction (e.g., a stenosis) in blood vessel 34. a These embodiments can provide the ability to take pressure measurements on both sides of a stenosis without having to reposition the device 10.

[0026] Regardless of whether one or more sensors are used, a set of first location pressure measurements may be obtained at a first location within a blood vessel over a first period of time, and a set of second location pressure measurements may be obtained at a second, different location within the blood vessel over the first period of time. This may also be applied to anatomical structures of interest other than blood vessels.

[0027] FIG. 2 shows a diagram of an exemplary embodiment of a system 70 for assessing the severity of a restriction at a location of interest in a blood vessel. The system 70 includes the sensor delivery device 10, as detailed with respect to FIG. 1, as well as a computing device 75. The computing device 75 may be connected to the sensor 40, such as via a communication channel 60, to receive one or more signals generated by the sensor 40 representative of a physiological parameter (e.g., pressure) in the blood vessel. The computing device 75 may include one or more programmable processors, as well as a non-transitory computer-readable storage article having computer-executable instructions stored therein. The computer-executable instructions may cause the at least one programmable processor to process signals from the sensor 40 (and any other sensors used in a particular application) and output information that may be useful in evaluating the blood vessel. For example, these computer-executable instructions may cause the at least one programmable processor to process signals from the sensor 40 (and any other sensors used in a particular application) to output information that may be useful in evaluating the blood vessel. d and the measured aortic pressure in the blood vessel, P a A value may be calculated based on the endovascular pressure and can provide a value as an assessment of intravascular restriction.

[0028] The computing device 75 can include a user interface 80. The one or more programmable processors can process the signal(s) from the sensor(s) and cause the user interface 80 to present a display of information related to the physiological parameter(s) measured within the blood vessel. When the system 70 is used in an application to approximate FFR, the one or more programmable processors can process the pressure signal(s) from the sensor(s) as described herein, and the user interface 80 can present a numerical approximation of the FFR. In some such cases, the user interface 80 can display the aortic pressure P a Display of pressure waveform as a function of time and / or distal pressure P dA display of the pressure waveform as a function of time may be presented. The user interface 80 may also present additional useful information, such as navigation functions and status information regarding the sensor delivery device 10 and / or the patient.

[0029] As described above, the sensor delivery device 10 and system 70 may be used in evaluating a blood vessel. In particular, the sensor delivery device 10 may be used to obtain a set of pressure measurements at a first location within the blood vessel over a first time period, and a set of pressure measurements at a second, different location within the blood vessel over the first time period. For example, when these sets of pressure measurements are used to approximate an FFR, the first location may be on a first side of a stenosis within the blood vessel, and the second location may be on a second, opposite side of the stenosis within the blood vessel, as detailed above. An embodiment of a technique for using (e.g., processing) such a set of pressure measurements to approximate an FFR is described below.

[0030] To properly assess the severity of a stenosis, it is generally necessary to minimize vascular resistance. In conventional FFR, this is accomplished by administering a hyperemic drug, such as adenosine, to induce maximal hyperemia in the blood vessel, and then taking a pressure measurement during the induced maximal hyperemia. The techniques disclosed herein, as well as devices, systems, and computer executable instructions, can use pressure measurements obtained in the blood vessel when not hyperemic (i.e., during a non-hyperemic state), thus precluding the administration of hyperemic drugs, or in some cases, any type of drug. Instead, these embodiments can identify characteristics associated with pressure measurements obtained when not hyperemic, and use these identified characteristics to select pressure measurements when vascular resistance is naturally at a minimum. These selected pressure measurements can then be used to calculate a pressure ratio. Because embodiments of the techniques disclosed herein can use pressure measurements obtained when not hyperemic, the calculated pressure ratio can be referred to as an approximation of the FFR. While the embodiments disclosed herein may provide certain advantages by eliminating the need for hyperemia (e.g., by administration of a hyperemic agent), it should be understood that any of the embodiments disclosed herein may be used in hyperemic conditions.

[0031] 3A and 3B show graphical representations 100A, 100B of a first location set 102 and a second location set 104 of pressure measurements, respectively. The first location set 102 of pressure measurements may include several individual pressure measurements taken at a first location within the vessel over a first time period 106. The second location set 104 of pressure measurements may include several individual pressure measurements taken at a second, different location within the vessel, taken over the same first time period 106. In one example, the first location set 102 of pressure measurements may be taken at a location distal to the region of interest (e.g., a restriction such as a stenosis), thus determining the distal pressure P d, whereas a second set of location pressure measurements 104 may be taken at a location proximal to the region of interest (e.g., a restriction such as a stenosis) or in a direction toward the aorta therefrom, thus referring to the aortic pressure P a The first time period 106 may represent a non-congestive state in the blood vessel such that the set of pressure measurements at the first location 102 and the set of pressure measurements at the second location 104 are taken when there is no congestion.

[0032] 3A and 3B, for illustrative purposes, graphically depict each of the set of pressure measurements at a first location 102 and the set of pressure measurements at a second location 104 as a pressure waveform as a function of a first time period 106. However, in certain embodiments of techniques within the scope of this disclosure, the set of pressure measurements at a first location 102 and the set of pressure measurements at a second location 104 may be used without the need to generate a graphical waveform, for example, in the form of a numerical data set including individual measured pressures and corresponding times.

[0033] 3A and 3B, the set of pressure measurements at the first location 102 includes a dicrotic notch 108, and the set of pressure measurements at the second location 104 includes a dicrotic notch 110. In the exemplary diagnostic application described herein, the dicrotic notches 108, 110 represent the closure of the aortic valve at the beginning of ventricular diastole during the cardiac cycle 112. Each dicrotic notch 108, 110 appears in the respective pressure waveform as a relatively slight upward deflection in the descending portion of the pressure waveform. In other words, each dicrotic notch 108, 110 is represented by one or more increasing pressure measurements in the respective set of pressure measurements, with a decreasing pressure measurement immediately preceding and following the one or more increasing pressure measurements in time.

[0034] As previously discussed, past techniques for approximating FFR rely on identifying the diastolic phase of the cardiac cycle and using pressure measurements taken during a predefined subperiod of diastole, sometimes referred to as a "wave-free period," when vascular resistance is empirically found to be low. To identify the beginning of diastole, these past techniques rely on identifying the dicrotic notch 108, 110 in each set of pressure measurements. Using the identified dicrotic notch 108, 110 as a reference point, these past techniques then define a subperiod within diastole relative to the dicrotic notch 108, 110, where the pressure measurements are used in calculating the pressure ratio. Because these past FFR approximation techniques define the period (e.g., diastole) where the pressure measurements are used relative to the dicrotic notch, failure to accurately identify the dicrotic notch in pressure measurements taken on a particular patient is problematic. That is, the pressure ratio may be calculated using pressure measurements taken when vascular resistance is significant and detrimental to the pressure measurements, leading to an inaccurate approximation of the FFR.

[0035] 3A and 3B show idealized waveforms for illustrative purposes, in reality, as a result of various anatomical conditions, the dicrotic notch may be difficult to detect across many patients, and in some cases, the dicrotic notch may not be detected at all. For example, depending on a particular patient, the dicrotic notch may be accompanied by several other upward deflections in the descending portion of the pressure waveform. This makes it difficult to identify which of such deflections are dicrotic notches (e.g., representing the closure of the aortic valve) and which of the other deflections are simply noise associated with a particular patient's anatomy. In other examples, depending on a particular patient's anatomy, there may be no upward deflections in the descending portion of the pressure waveform, and therefore no detectable dicrotic notch.

[0036] Thus, various embodiments of the techniques disclosed herein may identify characteristics associated with pressure measurements at times other than when the dicrotic notch is present (e.g., taken when not hyperemic). For example, the types of characteristics identified by the techniques disclosed herein may include, by way of example, one or more of a maximum pressure measurement, a minimum pressure measurement, a maximum or threshold decreasing pressure measurement rate of change, and a maximum increasing pressure measurement rate of change. The characteristics identified in these embodiments may be more easily and consistently identified across a range of patients compared to the dicrotic notch. These embodiments may then use the identified characteristic to select a pressure measurement therefor (e.g., one or more pressure measurements taken from time to time between the identified characteristic) and use the selected pressure measurement to calculate a numerical value, such as a pressure ratio, that approximates the FFR. For example, the pressure measurement used in calculating the pressure ratio may be selected relative to the identified characteristic, such that the selected pressure measurement is one obtained when vascular resistance is shown to be naturally minimized. Such embodiments may thus reduce patient side effects, as well as costs and time, associated with inducing hyperemia in conventional FFR, while at the same time providing a more consistent and accurate approximation of the FFR by eliminating the need to identify the dicrotic notch.

[0037] One exemplary embodiment of such a technique for calculating a pressure ratio to approximate an FFR is described with reference to Figures 3A and 3B. In the exemplary embodiment described with reference to Figures 3A and 3B, the technique uses a maximum pressure measurement as a type of characteristic to be identified and used to select an associated pressure measurement for use in calculating a pressure ratio that approximates an FFR. This exemplary technique is described with reference to Figure 3A. Next, with reference to Figure 3B, certain aspects of independent characteristic identification for each of the first location set of pressure measurements 102 and the second location set of pressure measurements 104 that may be used in this exemplary technique are described.

[0038] A first pre-characteristic 114 and a first post-characteristic 116 are identified for the set of pressure measurements at the first location 102. The identified first post-characteristic 116 follows the identified first pre-characteristic 114 in the first time period 106. The first pre-characteristic 114 is associated with one or more pressure measurements in the set of pressure measurements at the first location 102, and the first post-characteristic 116 is associated with one or more pressure measurements in the set of pressure measurements at the first location 102. The one or more pressure measurements in the set of pressure measurements at the first location 102 with which the first post-characteristic 116 is associated may be different (e.g., obtained at a different time) than the one or more pressure measurements in the set of pressure measurements at the first location 102 with which the first pre-characteristic 114 is associated.

[0039] In particular, in the embodiment of the technique described with reference to Figures 3A and 3B, the first pre-characteristic 114 and the first post-characteristic 116 are characteristics identified as the maximum pressure readings in the set of pressure readings 102 at the first location. In the example shown, the first pre-characteristic 114 is identified as the maximum pressure readings in the set of pressure readings 102 at the first location within a first predetermined time interval 122 of the first time period 106. Also, in the example shown, the first post-characteristic 116 is identified as the maximum pressure readings in the set of pressure readings 102 at the first location within a second predetermined time interval 124 of the first time period 106 following the first predetermined time interval 122. The first pre-defined time interval 122 and the second pre-defined time interval 124 may be set as appropriate depending on the particular application. In some examples, the first pre-defined time interval 122 and the second pre-defined time interval 124 will be set to be consecutive and equal in duration. In the example shown, the first predetermined time interval 122 is set to approximate the time it typically takes for one cardiac cycle 112 (e.g., for a particular patient in an application). The second predetermined time interval 124 may be similarly set to approximate the time it typically takes for another successive cardiac cycle 112.

[0040] The first anterior characteristic 114 and the first posterior characteristic 116 are not associated with pressure measurements representative of the dicrotic notch 108. Instead, the first anterior characteristic 114 and the first posterior characteristic 116 are each associated with one or more pressure measurements in the set of pressure measurements at the first location 102 taken at a time within the first period 106 (e.g., time 126, time 128) that is different from a time within the first period 106 at which the dicrotic notch 108 is present in the set of pressure measurements at the first location 102.

[0041] A second pre-characteristic 118 and a second post-characteristic 120 are identified for the set of pressure measurements at the second location 104. The identified second post-characteristic 120 follows the identified second pre-characteristic 118 in the first time period 106. The second pre-characteristic 118 is associated with one or more pressure measurements in the set of pressure measurements at the second location 104, and the second post-characteristic 120 is associated with one or more pressure measurements in the set of pressure measurements at the second location 104. The one or more pressure measurements in the set of pressure measurements at the second location 104 with which the second post-characteristic 120 is associated may be different (e.g., obtained at a different time) than the one or more pressure measurements in the set of pressure measurements at the second location 104 with which the second pre-characteristic 118 is associated.

[0042] In particular, in the embodiment of the technique described with reference to FIGS. 3A and 3B, the second pre-characteristic 118 and the second posterior characteristic 120 are characteristics identified as maximum pressure measurements in the set of pressure measurements at the second location 104. In the example shown here, the second pre-characteristic 118 may be identified as the maximum pressure measurement in the set of pressure measurements at the second location 104 within a first predetermined time interval 122. Also, in the example shown here, the second posterior characteristic 120 may be identified as the maximum pressure measurement in the set of pressure measurements at the second location 104 within a second predetermined time interval 124. In some cases, the identified maximum pressure measurement may represent two or more individual pressure measurements in the set of pressure measurements at the first location 102 and / or the set of pressure measurements at the second location 104. For example, in either or both of these sets, the identified maximum pressure measurement may be identified as corresponding to an average time of the respective predetermined time interval representing a plurality of consecutive local pressure measurements that are greater than other pressure measurements adjacent in time by a predetermined amount. This may be useful, in one embodiment, to align identified pre-characteristics and / or post-characteristics from different sets 102, 104 at a common time within each predetermined time interval.

[0043] The second anterior characteristic 118 and the second posterior characteristic 120 are not associated with pressure measurements representative of the dicrotic notch 110. Instead, the second anterior characteristic 118 and the second posterior characteristic 120 are each associated with one or more pressure measurements in the set of pressure measurements at the second location 104 taken at a time within the first period 106 (e.g., time 126, time 128) that is different from a time within the first period 106 at which the dicrotic notch 110 is present in the set of pressure measurements at the second location 104.

[0044] In some cases, as shown in FIG. 3A, the maximum pressure measurement identified as the first pre-characteristic 114 and the maximum pressure measurement identified as the second pre-characteristic 118 may be at the same time 126 within the first time period 106. Similarly, in some cases, as shown in FIG. 3A, the maximum pressure measurement identified as the first post-characteristic 116 and the maximum pressure measurement identified as the second post-characteristic 120 may be at the same time 128 within the first time period 106. However, as will be described with reference to FIG. 3B, in other cases, the maximum pressure measurement identified as the first pre-characteristic 114 and the maximum pressure measurement identified as the second pre-characteristic 118 may be at different times within the first time period 106, and the maximum pressure measurement identified as the first post-characteristic 116 and the maximum pressure measurement identified as the second post-characteristic 120 may be at different times within the first time period 106.

[0045] The identified pre-characteristics and post-characteristics may serve as criteria for selecting a pressure measurement used to calculate a pressure ratio. For example, a pressure measurement may be selected within the set of pressure measurements 102 for a first location between the identified first pre-characteristic 114 and the identified first post-characteristic 116. Similarly, a pressure measurement may be selected within the set of pressure measurements 104 for a second location between the identified second pre-characteristic 118 and the identified second post-characteristic 120. In one instance, the selected pressure measurements between the identified first pre-characteristic 114 and the identified first post-characteristic 116, and the selected pressure measurements between the second pre-characteristic 118 and the identified second post-characteristic 120 may be acquired simultaneously in a first period 106. A numerical value representing an assessment of a restriction in a vessel, such as a pressure ratio, may then be calculated using i) the selected pressure measurements between the identified first pre-characteristic 114 and the identified first post-characteristic 116, and ii) the selected pressure measurements between the second pre-characteristic 118 and the identified second post-characteristic 120. In other examples, pressure measurements can be selected for identified pre- and post-characteristics at locations other than between the identified pre- and post-characteristics.

[0046] For example, in some embodiments, two or more pressure measurements from each set between respective identified characteristics may be used to calculate a pressure ratio. As one such example, one pressure measurement in the set of pressure measurements 102 at a first location between the identified first pre-characteristic 114 and the identified first post-characteristic 116 may be averaged with another pressure measurement in the set of pressure measurements 102 at a first location between the identified first pre-characteristic 114 and the identified first post-characteristic 116. Similarly, one pressure measurement in the set of pressure measurements 104 at a second location between the identified second pre-characteristic 118 and the identified second post-characteristic 120 may be averaged with another pressure measurement in the set of pressure measurements 104 at a second location between the identified second pre-characteristic 118 and the identified second post-characteristic 120. The pressure ratio may then be calculated using the average pressure measurement in the set 102 of pressure measurements at a first location between the identified first pre-characteristic 114 and the identified first posterior characteristic 116, and the average pressure measurement in the set 104 of pressure measurements at a second location between the identified second pre-characteristic 118 and the identified second posterior characteristic 120.

[0047] In some cases, the one or more pressure measurements used to calculate the pressure ratio may be selected at a particular location between the respective pre-characteristics and post-characteristics. For example, the pressure ratio may be calculated using i) a pressure measurement 132 that is a first distance 130 (e.g., as measured in time, and therefore may be referred to as time 130) between the identified first pre-characteristic 114 and the identified first post-characteristic 116, and ii) a pressure measurement 134 that is a first distance 130 (e.g., as measured in time, and therefore may be referred to as time 130) between the identified second pre-characteristic 118 and the identified second post-characteristic 120. In the example shown in FIG. 3A, the first distance is 130, which is midway (e.g., as measured in time) between the identified first pre-characteristic 114 and the identified first post-characteristic 116, and midway (e.g., as measured in time) between the identified second pre-characteristic 118 and the identified second post-characteristic 120. Thus, as shown, the first distance 130 is 50 percent of the time 129 spanning between the time 126 associated with each of the before characteristics 114 , 118 and the time 128 associated with each of the after characteristics 116 , 120 .

[0048] In those embodiments described above in which two or more pressure measurements from each set between each identified characteristic are used to calculate the pressure ratio, each of these two or more pressure measurements may also be selected at a particular location between the respective pre- and post-characteristics. In the example shown in Figure 3A, in addition to using pressure measurements 132, 134 at the first distance 130, a pressure measurement at a second distance 136 and / or a pressure measurement at a third distance 142 may be used.

[0049] For example, i) a pressure measurement 138 that is a second distance 136 between the identified first pre-characteristic 114 and the identified first post-characteristic 116, and ii) a pressure measurement 140 that is a second distance 136 between the identified second pre-characteristic 118 and the identified second post-characteristic 120, may each be used with the pressure measurements 132, 134 to calculate a pressure ratio. The second distance 136 may be between the time 126 and the time at which the first distance 130 is set, and may be, for example, 20 percent, 25 percent, 30 percent, 35 percent, 40 percent, or 45 percent of the time 129.

[0050] Additionally, a pressure measurement 144, i) which is a third distance 142 between the identified first pre-characteristic 114 and the identified first post-characteristic 116, and a pressure measurement 146, ii) which is a third distance 142 between the identified second pre-characteristic 118 and the identified second post-characteristic 120, may each be used with the pressure measurements 132, 134 in addition to or as an alternative to the pressure measurements 138, 140 to calculate a pressure ratio. The third distance 142 may be between the time 128 and the time at which the first distance 130 is set, and may be, for example, 55 percent, 60 percent, 65 percent, 70 percent, 75 percent, 80 percent, 85 percent, or 90 percent of the time 129.

[0051] These two or more pressure measurements from each set at a particular location between the respective pre- and post-characteristics may be combined and used to calculate a pressure ratio. For example, pressure measurement 132 may be averaged with pressure measurement 138 and / or 144. Similarly, pressure measurement 134 may be averaged with pressure measurement 140 and / or 146. A pressure ratio may then be calculated using the average pressure measurement at a particular location in the set 102 of pressure measurements at a first location between the identified first pre-characteristic 114 and the identified first post-characteristic 116, and the average pressure measurement at a particular location in the set 104 of pressure measurements at a second location between the identified second pre-characteristic 118 and the identified second post-characteristic 120.

[0052] As noted above, Figure 3B illustrates an example of a particular aspect of independent characteristic identification for each of the first location set 102 and the second location set 104. Once one or more characteristics have been independently identified in each of the first location set 102 and the second location set 104, these one or more characteristics may be used to select one or more pressure measurements in each of the first location set 102 and the second location set 104 and calculate the same or similar values ​​as described elsewhere herein (e.g., with respect to Figure 3A). As in the example described with reference to Figure 3A, in the example of Figure 3B, the first pre-characteristic 114 and the first post-characteristic 116 are characteristics identified as the maximum pressure measurements in the first location set 102, and the second pre-characteristic 118 and the second post-characteristic 120 are characteristics identified as the maximum pressure measurements in the second location set 104. However, any one or more of the aspects disclosed with reference to FIG. 3B may be used in conjunction with several other feature types disclosed elsewhere herein (e.g., any one or more of the feature identifications disclosed with reference to FIGS. 4, 5, 6, 7, and 8).

[0053] 3B, a pressure waveform representing a set of pressure measurements at a first location 102 may be offset or shifted in a first time period 106 relative to a pressure waveform representing a set of pressure measurements at a second location 104. This may occur in certain example applications when the set of pressure measurements at the first location 102 and the set of pressure measurements at the second location 104 are taken at different locations that experience pressure changes at different times due to the distance between these different locations.

[0054] In the example described with reference to FIG. 3B , the first pre-characteristic 114 and the first post-characteristic 116 are identified in the set of pressure measurements at the first location 102 independent of the second pre-characteristic 118 and the second post-characteristic 120 in the set of pressure measurements at the second location 104. As shown, the first pre-characteristic 114 is identified as the maximum pressure measurement in the set of pressure measurements at the first location 102 and the second pre-characteristic 118 is identified as the maximum pressure measurement in the set of pressure measurements at the second location 104 within a first predetermined time interval 122 of the first time period 106. That is, the first pre-characteristic 114 is identified as the maximum pressure measurement in the set of pressure measurements at the first location 102 at a time 126d. The second pre-characteristic 118 is identified as the maximum pressure measurement in the set of pressure measurements at the second location 104 at a time 126a that is different from the time 126d. As also shown herein, the first posterior characteristic 116 is identified as the maximum pressure measurement in the set of pressure measurements 102 at the first location, and the second posterior characteristic 120 is identified as the maximum pressure measurement in the set of pressure measurements 104 at the second location within a second predetermined time interval 124 of the first time period 106. That is, the first posterior characteristic 116 is identified as the maximum pressure measurement in the set of pressure measurements 102 at the first location at a time 128d. The second posterior characteristic 120 is identified as the maximum pressure measurement in the set of pressure measurements 104 at the second location at a time 128a that is different from time 128d.

[0055] As previously discussed, the first anterior characteristic 114 , the first posterior characteristic 116 , the second anterior characteristic 118 , and the second posterior characteristic 120 are not related to pressure measurements representative of the respective dicrotic notches 108 , 110 .

[0056] 3B, the identified leading and trailing characteristics may serve as criteria for selecting a pressure measurement to be used to calculate a pressure ratio. For example, a pressure measurement may be selected within the set of pressure measurements 102 for a first location between an identified first leading characteristic 114 and an identified first trailing characteristic 116. Similarly, a pressure measurement may be selected within the set of pressure measurements 104 for a second location between an identified second leading characteristic 118 and an identified second trailing characteristic 120.

[0057] As an example, as shown in FIG. 3B, one or more pressure measurements used to calculate the pressure ratio may be selected at a particular location between the respective pre-characteristics and post-characteristics. For example, the pressure ratio may be calculated using a pressure measurement 132 that is a first distance 130d (e.g., as measured in time, and therefore may be referred to as time 130d) between the identified first pre-characteristic 114 and the identified first post-characteristic 116, and / or a pressure measurement 134 that is a first distance 130a (e.g., as measured in time, and therefore may be referred to as time 130a) between the identified second pre-characteristic 118 and the identified second post-characteristic 120. As shown in the example of FIG. 3B, the first distance is 130d, which is midway (e.g., as measured in time) between the identified first pre-characteristic 114 and the identified first post-characteristic 116. Thus, as shown, the first distance 130d is 50 percent of the time 129d spanning between the time 126d associated with the first pre-characteristic 114 and the time 128d associated with the first post-characteristic 116. And the first distance 130a is midway (e.g., as measured in time) between the identified second pre-characteristic 118 and the identified second post-characteristic 120. Thus, as shown, the first distance 130a is 50 percent of the time 129a spanning between the time 126a associated with the second pre-characteristic 116 and the time 128a associated with the second post-characteristic 120. In FIG. 3B, the pressure waveform representing the set of pressure measurements 102 at the first location is offset in the first period 106 relative to the pressure waveform representing the set of pressure measurements 104 at the second location, so that the first distance 130a may be offset from the first distance 130d. As shown here, first distance 130a is offset from first distance 130d by time 148.

[0058] The pressure ratio may be calculated using pressure measurements 132 and / or 134 in a variety of ways. As one example, the pressure ratio may be calculated using i) pressure measurement 132 in the set of pressure measurements 102 at the first location at a time corresponding to 130d, and ii) pressure measurement 134 in the set of pressure measurements 104 at the second location at a time corresponding to 130a. As another example, the pressure ratio may be calculated using i) pressure measurement 132 in the set of pressure measurements 102 at the first location at a time corresponding to 130d, and ii) pressure measurement 135 in the set of pressure measurements 104 at the second location at a time corresponding to 130d. Thus, in this example, pressure measurement 132 may be identified using pre-characteristics 114 and post-characteristics 116 as described, and then pressure measurement 135 may be identified as the pressure measurement in the set of pressure measurements 104 at the second location at a time within first period 106 that corresponds to pressure measurement 132. As a further example, a pressure ratio may be calculated using i) pressure measurement 134 in the set of pressure measurements 104 at the second location at a time corresponding to 130a, and ii) pressure measurement 133 in the set of pressure measurements 102 at the first location at a time corresponding to 130a. Thus, in this example, pressure measurement 134 may be identified using pre-characteristics 118 and post-characteristics 120 as described, and pressure measurement 133 may then be identified as the pressure measurement in the set of pressure measurements 102 at the first location at a time within first time period 106 that corresponds to pressure measurement 134.

[0059] In some instances where the pressure waveforms are offset, such as in FIG. 3B, a correction factor may be applied to calculate the pressure ratio. For example, in one embodiment, the pressure ratio may be calculated using a corrected pressure measurement calculated by applying a correction factor to i) the pressure measurement 132 in the set of pressure measurements 102 at the first location at a time corresponding to 130d, and ii) the pressure measurement 135 in the set of pressure measurements 104 at the second location at a time corresponding to 130d. The correction factor applied to the pressure measurement 135 may be a numerical multiplier (e.g., less than or greater than 1) that compensates the pressure measurement 135 for a timing offset between the pressure waveforms of the pressure measurements 102, 104 at the first and second locations. In one instance, the correction factor may be a numerical multiplier (e.g., less than or greater than 1) that compensates the pressure measurement 135 for an offset time 148. Thus, in this case, the correction factor may be a numerical multiplier corresponding to the offset time 148 to adjust the pressure measurement 135 for this offset time 148. Thus, here, the larger the offset time 148 , the larger the correction factor adjustment applied to the pressure measurement 135 .

[0060] In another example of the correction factor, the pressure ratio may be calculated using a corrected pressure measurement calculated by applying a correction factor to i) the pressure measurement 134 in the set of pressure measurements 104 at the second location at a time corresponding to 130a, and ii) the pressure measurement 133 in the set of pressure measurements 102 at the first location at a time corresponding to 130a. The correction factor applied to the pressure measurement 133 may be a numerical multiplier (e.g., less than or greater than 1) that compensates the pressure measurement 133 for a timing offset between the pressure waveforms of the pressure measurements 102, 104 at the first and second locations. In one case, the correction factor may be a numerical multiplier (e.g., less than or greater than 1) that compensates the pressure measurement 133 for an offset time 148. Thus, in this case, the correction factor may be a numerical multiplier corresponding to the offset time 148 to adjust the pressure measurement 133 for this offset time 148. Thus, here, the larger the offset time 148, the larger the adjustment of the correction factor applied to the pressure measurement 133.

[0061] In some examples, an electrocardiogram (sometimes abbreviated as ECG or EKG) may be used to help identify pre- and / or post-characteristic characteristics of one or more sets of pressure measurements. One or both of the pressure waveforms at the first and second locations may be compared to an electrocardiogram tracing. Through this comparison, a verifiable characteristic of the electrocardiogram tracing may be used to identify a corresponding characteristic of one or both of the pressure waveforms at the first and second locations. This may be useful when a particular characteristic of one or both of the pressure waveforms at the first and second locations that is sought to be identified is difficult to identify in isolation. This may be the case, for example, for a particular patient where two or more pressure measurements that are adjacent in time in the pressure waveform are close to a similar maximum pressure value. By comparing this pressure waveform to the patient's electrocardiogram tracing taken simultaneously with the pressure measurements, a readily verifiable characteristic of the electrocardiogram tracing may be used to determine which pressure measurement is identified as a maximum pressure measurement characteristic.

[0062] For example, an electrocardiogram may be used to identify maximum pressure measurements as each of the pre-characteristic and post-characteristic. In this example, the time of the peak of a first electrocardiogram tracing (sometimes referred to as the "R" wave or peak of ventricular contraction) may be determined. This time of the peak of the first electrocardiogram tracing may then be used as the time at which a pressure measurement in a set of pressure measurements (e.g., a set of pressure measurements at a first and / or second location) is identified as a pre-characteristic. Similarly, the time of the peak of a second subsequent electrocardiogram tracing may then be determined. This time of the peak of the second electrocardiogram tracing may then be used as the time at which a pressure measurement in a set of pressure measurements (e.g., a set of pressure measurements at a first and / or second location) is identified as a post-characteristic.

[0063] In other examples, the electrocardiogram can be used to help identify other types of leading and / or trailing characteristics in one or more sets of pressure measurements, including, for example, the types of leading and trailing characteristics disclosed with reference to Figures 4-8.

[0064] 4 shows a graphical representation 200 of pressure measurements taken over several predetermined time intervals of the first time period 106. According to one exemplary embodiment described herein with reference to FIG 4, a pressure ratio may be calculated using pressure measurements from each of two or more different predetermined time intervals. This helps to provide a larger sample size for calculating the pressure ratio, which may serve to increase accuracy.

[0065] 4, the first time period 106 includes a number of predetermined time intervals. As shown, the first time period 106 includes a first predetermined time interval 122 and a second predetermined time interval 124 following the first predetermined time interval 122. The set of pressure measurements 102 at the first location form a first location pressure waveform including a first cycle 160 of pressure measurements at the first location over the first predetermined time interval 122 and a second cycle 162 of pressure measurements at the first location over the second predetermined time interval 124. Similarly, the set of pressure measurements 104 at the second location form a second location pressure waveform including a first cycle 164 of pressure measurements at the second location over the first predetermined time interval 122 and a second cycle 166 of pressure measurements at the second location over the second predetermined time interval 124. In an exemplary application described herein, a first cycle of pressure readings at a first location 160 and a first cycle of pressure readings at a second location 164 may each correspond to a first cardiac cycle within which a first predetermined time interval 122 is established. Also, in this same exemplary application described herein, a second cycle of pressure readings at a first location 162 and a second cycle of pressure readings at a second location 166 may each correspond to a second cardiac cycle within which a second predetermined time interval 124 is established.

[0066] By taking pressure measurements over a number of different predefined time intervals set to correspond to different cycles, the pressure measurements from the different cycles can be used to calculate a pressure ratio. For example, a pressure ratio 168 for a first predefined time interval can be calculated using an average of one or more pressure measurements from a first cycle 160 of pressure measurements at a first location and one or more pressure measurements from a first cycle 164 of pressure measurements at a second location. Further, a pressure ratio 170 for a second predefined time interval can be calculated using an average of one or more pressure measurements from a second cycle 162 of pressure measurements at a first location and one or more pressure measurements from a second cycle 166 of pressure measurements at a second location. The pressure ratio 168 for the first predefined time interval and the pressure ratio 170 for the second predefined time interval can then be averaged to provide a pressure ratio calculated using pressure measurements from different cycles.

[0067] More specifically, as detailed above, one or more pressure measurements used from each of the cycles 160, 162, 164, 166 may be selected relative to identified leading and trailing characteristics.

[0068] A first pre-characteristic 114 and a first posterior characteristic 116 can be identified, and one or more pressure readings from a first cycle 160 of pressure readings at a first location can be selected between the identified first pre-characteristic 114 and first posterior characteristic 116. Also, a second pre-characteristic 118 and a second posterior characteristic 120 can be identified, and one or more pressure readings from a first cycle 164 of pressure readings at a second location can be selected between the identified second pre-characteristic 118 and second posterior characteristic 120. 4, a pressure ratio 168 for a first predetermined time interval may be calculated using i) a pressure measurement 132 from a first cycle 160 of pressure measurements at a first location that is midway between an identified first pre-characteristic 114 and a first post-characteristic 116 (or 50 percent of the time spanning between the time associated with the pre-characteristic 114 and the time associated with the post-characteristic 116), and ii) a pressure measurement 134 from a first cycle 164 of pressure measurements at a second location that is midway between an identified second pre-characteristic 118 and a second post-characteristic 120 (or 50 percent of the time spanning between the time associated with the pre-characteristic 118 and the time associated with the post-characteristic 120). As previously mentioned, pressure measurements at one or more other specific locations between the respective pre-characteristics 114, 118 and the respective post-characteristics 116, 120 may be used. Examples of such pressure measurements at one or more other specific locations between the respective pre-characteristics 114, 118 and the respective post-characteristics 116, 120 are shown in FIG. 4 along each respective waveform using visually unique markers, each of which is shown in detail by a key on the right side of FIG. 4.

[0069] To select one or more pressure readings from the second cycle 162 of pressure readings at the first location and one or more pressure readings from the second cycle 166 of pressure readings at the second location, the respective leading and trailing characteristics may again be identified. For example, a third leading characteristic may be identified that is associated with one or more pressure readings in the second cycle 162 of pressure readings at the first location, and a fourth leading characteristic may be identified that is associated with one or more pressure readings in the second cycle 166 of pressure readings at the second location. In the example shown in FIG. 4, the first trailing characteristic 116 serves as the third leading characteristic and the second trailing characteristic 120 serves as the fourth leading characteristic. Additionally, a third trailing characteristic 172 may be identified that is associated with one or more pressure readings in the third cycle 174 of pressure readings at the first location over a third predetermined time interval 150 of the first time period 106. And a fourth trailing characteristic 176 may be identified that is associated with one or more pressure readings in the third cycle 178 of pressure readings at the second location over the third predetermined time interval 150. In this example, the third posterior characteristic 172 and the fourth posterior characteristic 176 may each be a maximum pressure measurement in the respective sets of pressure measurements 102, 104 at the first and second locations over the third predetermined time period 150. The identified third posterior characteristic 172 may follow an identified third pre-characteristic in the set of pressure measurements 102 at the first location, and the identified fourth posterior characteristic 176 may follow an identified fourth pre-characteristic in the set of pressure measurements 104 at the second location.

[0070] One or more pressure measurements from the second cycle 162 of pressure measurements at the first location may be selected between the identified third pre-characteristic and the identified third post-characteristic 172. Also, one or more pressure measurements from the second cycle 166 of pressure measurements at the second location may be selected between the identified fourth pre-characteristic and the identified fourth post-characteristic 176. As shown in FIG. 4, the pressure ratio 170 for the second predetermined time interval may be calculated using i) a pressure measurement 180 from the second cycle 162 of pressure measurements at the first location that is halfway between the identified third pre-characteristic and the third post-characteristic 172 (or 50 percent of the time spanning between the time associated with the third pre-characteristic and the time associated with the third post-characteristic 172), and ii) a pressure measurement 182 from the second cycle 166 of pressure measurements at the second location that is halfway between the identified fourth pre-characteristic and the fourth post-characteristic 176 (or 50 percent of the time spanning between the time associated with the fourth pre-characteristic and the fourth post-characteristic 176). As previously mentioned, pressure measurements at one or more other specific locations between the respective third and fourth pre-characteristics and the respective third and fourth posterior characteristics 172, 176 may be used. Examples of such pressure measurements at one or more other specific locations between the respective third and fourth pre-characteristics and the respective third and fourth posterior characteristics 172, 176 are shown in Figure 4 along each respective waveform using visually unique markers, each of which is shown in detail by a key to the right of Figure 4.

[0071] Having calculated the pressure ratio 168 for the first predetermined time interval and the pressure ratio 170 for the second predetermined time interval, the pressure ratio over the two different cycles corresponding to the periods 122 and 124 may be calculated by averaging the pressure ratio 168 for the first predetermined time interval and the pressure ratio 170 for the second predetermined time interval.

[0072] In some embodiments, the pressure ratio may be calculated over three or more different cycles, as shown in FIG. 4. FIG. 4 further shows a fourth predetermined time interval 152 and a fifth predetermined time interval 154. In the same manner as just described, the pre- and post-characteristics may be identified and one or more pressure measurements located therebetween may be selected, which may then be used to calculate the pressure ratio of additional cycles to increase the sample size to provide an approximation of the FFR. In addition to calculating the first predetermined time interval pressure ratio 168 and the second predetermined time interval pressure ratio 170 as shown herein, a third predetermined time interval pressure ratio 184, a fourth predetermined time interval pressure ratio 186, and a fifth predetermined time interval pressure ratio 188 may also be calculated. Each of the predetermined time interval pressure ratios 168, 170, 184, 186, and 188 may be averaged to provide a pressure ratio calculated using pressure measurements from five different cycles, as shown in FIG. 4.

[0073] It should be noted that, as shown by the example of FIG. 4, an identified pre-characteristic may be associated with one or more pressure measurements occurring in a different cycle of pressure measurements than those one or more pressure measurements associated with the identified post-characteristic. For example, as shown herein, an identified first pre-characteristic 114 may be associated with one or more pressure measurements in a first cycle 160 of pressure measurements at a first location, while an identified first post-characteristic 116 may be associated with one or more pressure measurements in a second cycle 162 of pressure measurements at the first location. Similarly, an identified second pre-characteristic 118 may be associated with one or more pressure measurements in a first cycle 164 of pressure measurements at a second location, while an identified second post-characteristic 120 may be associated with one or more pressure measurements in a second cycle 166 of pressure measurements at the second location.

[0074] The exemplary embodiments disclosed thus far have been described and illustrated using maximum pressure measurements as one example of an identified characteristic type. Further exemplary embodiments are described below where other examples of identifiable characteristic types may be utilized.

[0075] Figure 5 again shows a graphical representation 100 of pressure measurements that may be used to calculate a pressure ratio. Details provided previously herein apply equally to the embodiment described with respect to Figure 5 unless otherwise noted. In particular, Figure 5 shows a further exemplary embodiment of a technique for calculating a pressure ratio to approximate an FFR, in which a characteristic type of the minimum pressure measurement is identified and used to select an associated pressure measurement for use in calculating a pressure ratio that approximates an FFR.

[0076] 5 illustrates a graphical representation 100 of a set of pressure measurements at a first location 102 and a set of pressure measurements at a second location 104 obtained over a first time period 106 as previously described. As shown again here, the set of pressure measurements at the first location 102 includes a dicrotic notch 108 and the set of pressure measurements at the second location 104 includes a dicrotic notch 110, where the dicrotic notches 108, 110 represent the closure of the aortic valve at the start of ventricular diastole during a cardiac cycle 112.

[0077] A first pre-characteristic 214 and a first post-characteristic 216 are identified for the set of pressure measurements at the first location 102. The identified first post-characteristic 216 follows the identified first pre-characteristic 214 in the first time period 106. The first pre-characteristic 214 is associated with one or more pressure measurements in the set of pressure measurements at the first location 102, and the first post-characteristic 216 is associated with one or more pressure measurements in the set of pressure measurements at the first location 102. The one or more pressure measurements in the set of pressure measurements at the first location 102 with which the first post-characteristic 216 is associated may be different (e.g., obtained at a different time) than the one or more pressure measurements in the set of pressure measurements at the first location 102 with which the first pre-characteristic 214 is associated.

[0078] As previously mentioned, in the exemplary embodiment described with reference to FIG. 5, a minimum pressure measurement is the type of characteristic to be used to identify and select the associated pressure measurement for use in calculating a pressure ratio that approximates the FFR. In particular, here, a first pre-characteristic 214 and a first posterior characteristic 216 are characteristics identified as the minimum pressure measurement in the set of pressure measurements 102 at the first location. In the example shown, the first pre-characteristic 214 is identified as the minimum pressure measurement in the set of pressure measurements 102 at the first location within a first predetermined time interval 122 of the first time period 106. Also, in the example shown, the first posterior characteristic 216 is identified as the minimum pressure measurement in the set of pressure measurements 102 at the first location within a second predetermined time interval 124 of the first time period 106 following the first predetermined time interval 122.

[0079] The first anterior characteristic 214 and the first posterior characteristic 216 are not associated with pressure measurements representative of the dicrotic notch 108. Instead, the first anterior characteristic 214 and the first posterior characteristic 216 are each associated with one or more pressure measurements in the set of pressure measurements at the first location 102 taken at a time within the first period 106 (e.g., time 226, time 228) that is different from a time within the first period 106 at which the dicrotic notch 108 is present in the set of pressure measurements at the first location 102.

[0080] A second pre-characteristic 218 and a second post-characteristic 220 are identified for the set of pressure measurements at the second location 104. The identified second post-characteristic 220 follows the identified second pre-characteristic 218 in the first time period 106. The second pre-characteristic 218 is associated with one or more pressure measurements in the set of pressure measurements at the second location 104, and the second post-characteristic 220 is associated with one or more pressure measurements in the set of pressure measurements at the second location 104. The one or more pressure measurements in the set of pressure measurements at the second location 104 with which the second post-characteristic 220 is associated may be different (e.g., obtained at a different time) than the one or more pressure measurements in the set of pressure measurements at the second location 104 with which the second pre-characteristic 218 is associated.

[0081] As mentioned, in the embodiment of the technique described with reference to FIG. 5, the second pre-characteristic 218 and the second posterior characteristic 220 are characteristics identified as minimum pressure readings in the set of pressure readings 104 at the second location. In the example shown here, the second pre-characteristic 218 may be identified as the minimum pressure reading in the set of pressure readings 104 at the second location within the first predetermined time interval 122. Also, in the example shown here, the second posterior characteristic 220 may be identified as the minimum pressure reading in the set of pressure readings 104 at the second location within the second predetermined time interval 124. In some cases, the identified minimum pressure reading may represent two or more individual pressure readings in the set of pressure readings 102 at the first location and / or the set of pressure readings 104 at the second location. For example, in either or both of these sets, the identified minimum pressure reading may be identified as corresponding to an average time in the respective predetermined time intervals representing multiple consecutive local minimum pressure readings, as shown for the first pre-characteristic 214. This may be useful, for example, to align identified pre- and / or post-characteristics from different sets 102, 104 at a common time within each predetermined time interval.

[0082] The second anterior characteristic 218 and the second posterior characteristic 220 are not associated with pressure measurements representative of the dicrotic notch 110. Instead, the second anterior characteristic 218 and the second posterior characteristic 220 are each associated with one or more pressure measurements in the set of pressure measurements 104 at the second location that are taken at a time within the first period 106 (e.g., time 226, time 228) that is different from a time within the first period 106 at which the dicrotic notch 110 is present in the set of pressure measurements 104 at the second location.

[0083] 5, the minimum pressure reading identified as the first pre-characteristic 214 and the minimum pressure reading identified as the second pre-characteristic 218 may be at the same time 226 within the first time period 106. Similarly, in some cases, the minimum pressure reading identified as the first post-characteristic 216 and the minimum pressure reading identified as the second post-characteristic 220 may be at the same time 228 within the first time period 106, as shown in FIG.

[0084] These identified pre- and post-characteristics may serve as criteria for selecting pressure measurements used in calculating the pressure ratio. For example, pressure measurements may be selected within the set of pressure measurements 102 for a first location between the identified first pre-characteristic 214 and the identified first post-characteristic 216. Similarly, pressure measurements may be selected within the set of pressure measurements 104 for a second location between the identified second pre-characteristic 218 and the identified second post-characteristic 220. In one instance, the selected pressure measurements between the identified first pre-characteristic 214 and the identified first post-characteristic 216 and the selected pressure measurements between the second pre-characteristic 218 and the identified second post-characteristic 220 may be acquired simultaneously in the first time period 106. The pressure ratio may then be calculated using i) the selected pressure measurements between the identified first pre-characteristic 214 and the identified first post-characteristic 216, and ii) the selected pressure measurements between the second pre-characteristic 218 and the identified second post-characteristic 220. In other examples, pressure measurements can be selected for identified pre- and post-characteristics at locations other than between the identified pre- and post-characteristics.

[0085] For example, two or more pressure measurements from each set between respective identified minimum pressure measurement characteristics 214, 216 and 218, 220 of Figure 5 may be used in calculating the pressure ratio in a manner similar to that described with reference to Figure 3. This may include selecting each of these two or more pressure measurements at one or more particular locations between the respective pre- and post-characteristics, in some cases combining these pressure measurements from the one or more particular locations, and using the combined pressure measurements to calculate the pressure ratio, as described with reference to Figure 3.

[0086] Also, in a similar manner as described with reference to FIG. 4, the pressure ratio may be calculated using characteristics of the identified minimum pressure measurement value associated with two or more different predetermined time intervals over the first period 106 to select a pressure measurement value from each of two or more of the different predetermined time intervals over the first period 106.

[0087] FIG. 6 again illustrates a graphical representation 100 of pressure measurements that may be used to calculate a pressure ratio. Details previously provided herein apply equally to the embodiment described with respect to FIG. 6 unless otherwise noted. In particular, FIG. 6 illustrates a further exemplary embodiment of a technique for calculating a pressure ratio to approximate an FFR, in which a characteristic type of maximum decreasing pressure measurement rate of change is used to select a pressure measurement associated therewith for use in calculating a pressure ratio to approximate an FFR. A maximum decreasing pressure measurement rate of change may be identified, for example, when a difference between successive pressure measurements constitutes a decrease in pressure that is a greater decrease in pressure than the difference between other successive pressure measurements obtained at different times. In the context of the pressure waveforms illustrated in FIG. 6, the maximum decreasing pressure measurement rate of change may be represented by a maximum downward slope in the waveform for each set 102, 104 of pressure measurements. As described in more detail below, a maximum decreasing pressure measurement rate of change characteristic may be identified within a predetermined time interval of a first period 106.

[0088] 6 illustrates a graphical representation 100 of a set of pressure measurements at a first location 102 and a set of pressure measurements at a second location 104 obtained over a first time period 106 as previously described. As shown again here, the set of pressure measurements at the first location 102 includes a dicrotic notch 108 and the set of pressure measurements at the second location 104 includes a dicrotic notch 110, where the dicrotic notches 108, 110 represent the closure of the aortic valve at the start of ventricular diastole during a cardiac cycle 112.

[0089] A first pre-characteristic 314 and a first post-characteristic 316 are identified for the set of pressure measurements at the first location 102. The identified first post-characteristic 316 follows the identified first pre-characteristic 314 in the first time period 106. The first pre-characteristic 314 is associated with one or more pressure measurements in the set of pressure measurements at the first location 102, and the first post-characteristic 316 is associated with one or more pressure measurements in the set of pressure measurements at the first location 102. The one or more pressure measurements in the set of pressure measurements at the first location 102 with which the first post-characteristic 316 is associated may be different (e.g., obtained at a different time) than the one or more pressure measurements in the set of pressure measurements at the first location 102 with which the first pre-characteristic 314 is associated.

[0090] As previously discussed, in the exemplary embodiment described with reference to FIG. 6, the maximum decreasing pressure measurement rate of change is the type of characteristic to be identified and used to select the associated pressure measurement for use in calculating a pressure ratio that approximates the FFR. In particular, here, the first pre-characteristic 314 and the first posterior characteristic 316 are characteristics identified as the maximum decreasing pressure measurement rate of change in the set of pressure measurements 102 at the first location. In the illustrated example, the first pre-characteristic 314 is identified as the maximum decreasing pressure measurement rate of change in the set of pressure measurements 102 at the first location within a first predetermined time interval 122 of the first time period 106. Also, in the illustrated example, the first posterior characteristic 316 is identified as the maximum decreasing pressure measurement rate of change in the set of pressure measurements 102 at the first location within a second predetermined time interval 124 of the first time period 106 following the first predetermined time interval 122.

[0091] The first anterior characteristic 314 and the first posterior characteristic 316 are not associated with pressure measurements representative of the dicrotic notch 108. Instead, the first anterior characteristic 314 and the first posterior characteristic 316 are each associated with one or more pressure measurements in the set of pressure measurements at the first location 102 taken at a time within the first period 106 (e.g., time 326, time 328) that is different from a time within the first period 106 at which the dicrotic notch 108 is present in the set of pressure measurements at the first location 102.

[0092] A second pre-characteristic 318 and a second post-characteristic 320 are identified for the set of pressure measurements at the second location 104. The identified second post-characteristic 320 follows the identified second pre-characteristic 318 in the first time period 106. The second pre-characteristic 318 is associated with one or more pressure measurements in the set of pressure measurements at the second location 104, and the second post-characteristic 320 is associated with one or more pressure measurements in the set of pressure measurements at the second location 104. The one or more pressure measurements in the set of pressure measurements at the second location 104 with which the second post-characteristic 320 is associated may be different (e.g., obtained at a different time) than the one or more pressure measurements in the set of pressure measurements at the second location 104 with which the second pre-characteristic 318 is associated.

[0093] As mentioned, in the embodiment of the technique described with reference to FIG. 6, the second pre-characteristic 318 and the second posterior characteristic 320 are characteristics identified as the maximum decreasing pressure measurement rate of change in the set of pressure measurements at the second location 104. In the example shown here, the second pre-characteristic 318 may be identified as the maximum decreasing pressure measurement rate of change in the set of pressure measurements at the second location 104 within the first predetermined time interval 122. Also, in the example shown here, the second posterior characteristic 320 may be identified as the maximum decreasing pressure measurement rate of change in the set of pressure measurements at the second location 104 within the second predetermined time interval 124. In some cases, the identified maximum decreasing pressure measurement rate of change may represent two or more individual pressure measurements in the set of pressure measurements at the first location 102 and / or the set of pressure measurements at the second location 104. For example, in either or both of these sets, the identified maximum decreasing pressure measurement rate of change may be identified as corresponding to a time within the respective predetermined time interval, which represents an average time of multiple local pressure measurements having the same or substantially similar decreasing rate of change therebetween. This may be useful, for example, to align identified pre- and / or post-characteristics from different sets 102, 104 at a common time within each predetermined time interval.

[0094] The second anterior characteristic 318 and the second posterior characteristic 320 are not associated with pressure measurements representative of the dicrotic notch 110. Instead, the second anterior characteristic 318 and the second posterior characteristic 320 are each associated with one or more pressure measurements in the set of pressure measurements 104 at the second location that are taken at a time within the first period 106 (e.g., time 326, time 328) that is different from a time within the first period 106 at which the dicrotic notch 110 is present in the set of pressure measurements 104 at the second location.

[0095] 6, the maximum decreased pressure measurement rate-of-change identified as the first pre-characteristic 314 and the maximum decreased pressure measurement rate-of-change identified as the second pre-characteristic 318 may be at the same time 326 within the first time period 106. Similarly, in some cases, the maximum decreased pressure measurement rate-of-change identified as the first post-characteristic 316 and the maximum decreased pressure measurement rate-of-change identified as the second post-characteristic 320 may be at the same time 328 within the first time period 106, as shown in FIG.

[0096] These identified pre-characteristics and post-characteristics may serve as criteria for selecting pressure measurements used in calculating the pressure ratio. For example, pressure measurements may be selected within the set of pressure measurements 102 for a first location between the identified first pre-characteristic 314 and the identified first post-characteristic 316. Similarly, pressure measurements may be selected within the set of pressure measurements 104 for a second location between the identified second pre-characteristic 318 and the identified second post-characteristic 320. In one instance, the selected pressure measurements between the identified first pre-characteristic 314 and the identified first post-characteristic 316 and the selected pressure measurements between the second pre-characteristic 318 and the identified second post-characteristic 320 may be acquired simultaneously in the first time period 106. The pressure ratio may then be calculated using i) the selected pressure measurements between the identified first pre-characteristic 314 and the identified first post-characteristic 316, and ii) the selected pressure measurements between the second pre-characteristic 318 and the identified second post-characteristic 320. In other examples, pressure measurements can be selected for identified pre- and post-characteristics at locations other than between the identified pre- and post-characteristics.

[0097] For example, two or more pressure measurements from each set between the respective identified maximum reduced pressure measurement rate of change characteristics 314, 316 and 318, 320 of Figure 6 may be used in calculating the pressure ratio in a manner similar to that described with reference to Figure 3. This may involve selecting each of these two or more pressure measurements at one or more particular locations between the respective pre- and post-characteristics, in some cases combining these pressure measurements from the one or more particular locations, and using the combined pressure measurements to calculate the pressure ratio, as described with reference to Figure 3.

[0098] Also, in a similar manner as described with reference to FIG. 4, the pressure ratio may be calculated using the identified maximum decreasing pressure measurement rate of change characteristics associated with two or more different predetermined time intervals over the first time period 106 to select pressure measurements from each of two or more of the different predetermined time intervals over the first time period 106.

[0099] FIG. 7 again illustrates a graphical representation 100 of pressure measurements that may be used to calculate a pressure ratio. Details provided previously herein apply equally to the embodiment described with respect to FIG. 7 unless otherwise noted. In particular, FIG. 7 illustrates a further exemplary embodiment of a technique for calculating a pressure ratio to approximate an FFR, in which a characteristic type of maximum incremental pressure measurement rate of change is used to select a pressure measurement associated therewith for use in calculating a pressure ratio to approximate an FFR. A maximum incremental pressure measurement rate of change may be identified, for example, when a difference between successive pressure measurements constitutes an increase in pressure that is a greater increase in pressure than the difference between other successive pressure measurements obtained at different times. In the context of the pressure waveforms illustrated in FIG. 7, the maximum incremental pressure measurement rate of change may be represented by a maximum upward slope in the waveform for each set 102, 104 of pressure measurements. As will be described in more detail below, a maximum incremental pressure measurement rate of change characteristic may be identified within a predetermined time interval of a first period 106.

[0100] 7 shows a graphical representation 100 of a set of pressure measurements at a first location 102 and a set of pressure measurements at a second location 104 obtained over a first time period 106 as described above. As shown again here, the set of pressure measurements at the first location 102 includes a dicrotic notch 108 and the set of pressure measurements at the second location 104 includes a dicrotic notch 110, where the dicrotic notches 108, 110 represent the closure of the aortic valve at the start of ventricular diastole during the cardiac cycle 112.

[0101] A first pre-characteristic 414 and a first post-characteristic 416 are identified for the set of pressure measurements at the first location 102. The identified first post-characteristic 416 follows the identified first pre-characteristic 414 in the first time period 106. The first pre-characteristic 414 is associated with one or more pressure measurements in the set of pressure measurements at the first location 102, and the first post-characteristic 416 is associated with one or more pressure measurements in the set of pressure measurements at the first location 102. The one or more pressure measurements in the set of pressure measurements at the first location 102 with which the first post-characteristic 416 is associated may be different (e.g., obtained at a different time) than the one or more pressure measurements in the set of pressure measurements at the first location 102 with which the first pre-characteristic 414 is associated.

[0102] As noted, in the exemplary embodiment described with reference to FIG. 7, the maximum incremental pressure measurement rate of change is the type of characteristic to be identified and used to select the associated pressure measurement for use in calculating a pressure ratio that approximates the FFR. In particular, the first pre-characteristic 414 and the first posterior characteristic 416 are characteristics identified as the maximum incremental pressure measurement rate of change in the set of pressure measurements 102 at the first location. In the example shown, the first pre-characteristic 414 is identified as the maximum incremental pressure measurement rate of change in the set of pressure measurements 102 at the first location within a first predetermined time interval 122 of the first time period 106. Also, in the example shown, the first posterior characteristic 416 is identified as the maximum incremental pressure measurement rate of change in the set of pressure measurements 102 at the first location within a second predetermined time interval 124 of the first time period 106 following the first predetermined time interval 122.

[0103] The first anterior characteristic 414 and the first posterior characteristic 416 are not associated with pressure measurements representative of the dicrotic notch 108. Instead, the first anterior characteristic 414 and the first posterior characteristic 416 are each associated with one or more pressure measurements in the set of pressure measurements at the first location 102 taken at a time within the first period 106 (e.g., time 426, time 428) that is different from a time within the first period 106 at which the dicrotic notch 108 is present in the set of pressure measurements at the first location 102.

[0104] A second pre-characteristic 418 and a second post-characteristic 420 are identified for the set of pressure measurements at the second location 104. The identified second post-characteristic 420 follows the identified second pre-characteristic 418 in the first time period 106. The second pre-characteristic 418 is associated with one or more pressure measurements in the set of pressure measurements at the second location 104, and the second post-characteristic 420 is associated with one or more pressure measurements in the set of pressure measurements at the second location 104. The one or more pressure measurements in the set of pressure measurements at the second location 104 with which the second post-characteristic 420 is associated may be different (e.g., obtained at a different time) than the one or more pressure measurements in the set of pressure measurements at the second location 104 with which the second pre-characteristic 418 is associated.

[0105] As mentioned, in the embodiment of the technique described with reference to FIG. 7, the second pre-characteristic 418 and the second posterior characteristic 420 are characteristics identified as the maximum increasing pressure measurement rate of change in the set of pressure measurements at the second location 104. In the example shown here, the second pre-characteristic 418 may be identified as the maximum increasing pressure measurement rate of change in the set of pressure measurements at the second location 104 within the first predetermined time interval 122. Also, in the example shown here, the second posterior characteristic 420 may be identified as the maximum increasing pressure measurement rate of change in the set of pressure measurements at the second location 104 within the second predetermined time interval 124. In some cases, the identified maximum increasing pressure measurement rate of change may represent two or more individual pressure measurements in the set of pressure measurements at the first location 102 and / or the set of pressure measurements at the second location 104. For example, in either or both of these sets, the identified maximum increasing pressure measurement rate of change may be identified as corresponding to a time within the respective predetermined time interval, which represents an average time of multiple local pressure measurements having the same or substantially similar decreasing rate of change therebetween. This may be useful, for example, to align identified pre- and / or post-characteristics from different sets 102, 104 at a common time within each predetermined time interval.

[0106] The second anterior characteristic 418 and the second posterior characteristic 420 are not associated with pressure measurements representative of the dicrotic notch 110. Instead, the second anterior characteristic 418 and the second posterior characteristic 420 are each associated with one or more pressure measurements in the set of pressure measurements 104 at the second location that are taken at a time within the first period 106 (e.g., time 426, time 428) that is different from a time within the first period 106 at which the dicrotic notch 110 is present in the set of pressure measurements 104 at the second location.

[0107] 7, the maximum increasing pressure measurement rate-of-change identified as the first pre-characteristic 414 and the maximum increasing pressure measurement rate-of-change identified as the second pre-characteristic 418 may be at the same time 426 within the first time period 106. Similarly, in some cases, the maximum increasing pressure measurement rate-of-change identified as the first post-characteristic 416 and the maximum increasing pressure measurement rate-of-change identified as the second post-characteristic 420 may be at the same time 428 within the first time period 106, as shown in FIG.

[0108] These identified pre-characteristics and post-characteristics may serve as criteria for selecting pressure measurements used in calculating the pressure ratio. For example, pressure measurements may be selected within the set of pressure measurements 102 for a first location between the identified first pre-characteristic 414 and the identified first post-characteristic 416. Similarly, pressure measurements may be selected within the set of pressure measurements 104 for a second location between the identified second pre-characteristic 418 and the identified second post-characteristic 420. In one instance, the selected pressure measurements between the identified first pre-characteristic 414 and the identified first post-characteristic 416 and the selected pressure measurements between the second pre-characteristic 418 and the identified second post-characteristic 420 may be acquired simultaneously in the first time period 106. The pressure ratio may then be calculated using i) the selected pressure measurements between the identified first pre-characteristic 414 and the identified first post-characteristic 416, and ii) the selected pressure measurements between the second pre-characteristic 418 and the identified second post-characteristic 420. In other examples, pressure measurements can be selected for identified pre- and post-characteristics at locations other than between the identified pre- and post-characteristics.

[0109] For example, two or more pressure measurements from each set between the respective identified maximum incremental pressure measurement rate of change characteristics 414, 416 and 418, 420 of Figure 7 may be used in calculating the pressure ratio in a manner similar to that described with reference to Figure 3. This may involve selecting each of these two or more pressure measurements at one or more particular locations between the respective pre- and post-characteristics, in some cases combining these pressure measurements from the one or more particular locations, and using the combined pressure measurements to calculate the pressure ratio, as described with reference to Figure 3.

[0110] Also, in a similar manner as described with reference to FIG. 4, the pressure ratio may be calculated using the identified maximum incremental pressure measurement rate of change characteristics associated with two or more different predetermined time intervals over the first time period 106 to select pressure measurements from each of two or more of the different predetermined time intervals over the first time period 106.

[0111] Figure 8 illustrates a graphical representation 500 of pressure measurements that may be used to calculate a pressure ratio. Details provided previously herein apply equally to the embodiment described with respect to Figure 8 unless otherwise noted. In particular, Figure 8 illustrates another exemplary embodiment of a technique for calculating a pressure ratio to approximate an FFR, in which a threshold decreasing pressure measurement rate of change characteristic type is used to select pressure measurements identified and associated therewith for use in calculating a pressure ratio that approximates an FFR.

[0112] In applications where pressure measurements are obtained over a cardiac cycle for some patients, e.g., in each such cycle, the pressure measurements may include two different time intervals where the pressure measurements over the respective time intervals decrease within a threshold rate of change. For example, as shown in FIG. 8, over a cardiac cycle 112, the set of pressure measurements 102 at a first location includes a first interval 124a where a group 530 of pressure measurements decreases from one pressure measurement to successive pressure measurements in the group 530 of pressure measurements within a threshold rate of change. Also, over a cardiac cycle 112, the set of pressure measurements 102 at a first location includes a second interval 124b where a group 532 of pressure measurements decreases from one pressure measurement to successive pressure measurements in the group 532 of pressure measurements within another threshold rate of change that is different from the one threshold rate of change of the group 530. Similarly, over the cardiac cycle 112, the set of pressure measurements 104 at the first location includes a first interval 122a during which the group 534 of pressure measurements decreases from one pressure measurement to successive pressure measurements in the group 534 of pressure measurements within a threshold rate of change. And over the cardiac cycle 112, the set of pressure measurements 104 at the first location includes a second interval 122b during which the group 536 of pressure measurements decreases from one pressure measurement to successive pressure measurements in the group 536 of pressure measurements within another threshold rate of change that is different from the one threshold rate of change of the group 534.

[0113] The threshold percentage change used to identify a group of pressure readings may vary depending on the particular application. For example, a group of pressure readings may be identified as such if the pressure readings over a time interval decrease by less than 0.5%, 1%, 2%, 3%, 5%, 7.5%, 10%, 15%, 20%, or 25% from one pressure reading to successive pressure readings in the time interval.

[0114] Groups 530 and 532 of the set of pressure measurements at a first location 102 and groups 534 and 536 of the set of pressure measurements at a second location 104 are referenced in Figure 8 in different cardiac cycles 112 for ease of explanation. However, in many embodiments, groups 530 and 532 of the set of pressure measurements at a first location 102 and groups 534 and 536 of the set of pressure measurements at a second location 104 may be analyzed and used from the same cardiac cycle 112.

[0115] A threshold decreasing pressure reading rate of change may be identified when the pressure readings in each set 102, 104 transition from one group with one threshold rate of change to another group with another different threshold rate of change. For example, a threshold decreasing pressure reading rate of change 514 may be identified for the set of pressure readings 102 at the first location over a predetermined time interval (e.g., as shown here, the first predetermined time interval 122 and / or the second predetermined time interval 124) when the pressure readings transition from group 530 of pressure readings to group 532 of pressure readings. Thus, the threshold decreasing pressure reading rate of change 514 in this example represents a time when the decrease in pressure between the pressure reading just before the time for the threshold decreasing pressure reading rate of change 514 and the pressure reading just after the time for the threshold decreasing pressure reading rate of change 514 is greater than the threshold rate of change. Similarly, a threshold decreasing pressure measurement rate of change 516 can be identified for the set of pressure measurements 104 at the first location over a predetermined time interval (e.g., first predetermined time interval 122 as shown here, and / or second predetermined time interval 124) as the pressure measurements transition from group of pressure measurements 534 to group of pressure measurements 536. Thus, the threshold decreasing pressure measurement rate of change 516 in this example represents a time when the decrease in pressure between the pressure measurement immediately prior to the time for the threshold decreasing pressure measurement rate of change 516 and the pressure measurement immediately after the time for the threshold decreasing pressure measurement rate of change 516 is greater than the threshold rate of change.

[0116] The identified threshold decreasing pressure measurement rate-of-change characteristic may serve as a criterion for selecting a pressure measurement used to calculate the pressure ratio. For example, a pressure measurement may be selected in the set of pressure measurements at the first location 102 as being at a particular location (e.g., time) relative to the threshold decreasing pressure measurement rate-of-change 514. Similarly, a pressure measurement may be selected in the set of pressure measurements at the second location 104 as being at a particular location (e.g., time) relative to the threshold decreasing pressure measurement rate-of-change 516. In certain embodiments, the threshold decreasing pressure measurement rate-of-change characteristic may be identified along with one or more other characteristic types disclosed herein. In such embodiments, the pressure measurements in the sets 102 and / or 104 may be selected to be at a particular location relative to the identified threshold decreasing pressure measurement rate-of-change characteristic and one or more identified other characteristic types disclosed herein. For example, one or more pressure measurements taken at a time between the identified threshold decreasing pressure measurement rate-of-change characteristic and one of the identified maximum pressure measurement, minimum pressure measurement, maximum decreasing pressure measurement rate-of-change, and maximum increasing pressure measurement rate-of-change may be selected for use in calculating the pressure ratio.

[0117] Identifying a threshold decreasing pressure measurement rate of change can serve as a reliable means for selecting an appropriate pressure measurement to use in calculating a pressure ratio to approximate the FFR. For example, as graphical representation 500 shows, a threshold decreasing pressure measurement rate of change can be identified without considering the dicrotic notch. This can be useful when the set of pressure measurements does not include any identifiable dicrotic notch, as is the case in FIG. 8 for the set of pressure measurements 102 at the first location.

[0118] 9 illustrates a flow diagram of an exemplary embodiment of a method 600 for evaluating a blood vessel. For example, the method described with reference to FIG. 9 may be implemented as an action taken by a user, as an algorithm implemented by computer-executable instructions stored in a non-transitory computer-readable storage article that causes at least one programmable processor to perform the action, or as a combination including both user and algorithm implementation.

[0119] At step 610, pressure measurements are taken. This step may include taking a set of first location pressure measurements at a first location within the blood vessel over a first period of time. This step may also include taking a set of second location pressure measurements at a second location within the blood vessel over the first period of time. The second location may be different from the first location. Additionally, at this step, the set of first location pressure measurements and the set of second location pressure measurements may be taken when not hyperemic.

[0120] In some cases, method 600 may include step 620. At step 620, a pre-check may be performed. The pre-check may be performed on one or more data points and used to determine whether such data is suitable for use in method 600. Performing a pre-check may include, for example, determining whether a set of pressure measurements at a first location and a set of pressure measurements at a second location meet a set of pre-check conditions, and if the set of pre-check conditions are met, identifying pre- and post-characteristics and calculating a pressure ratio.

[0121] In one example, the set of pre-check conditions may include a minimum pressure reading in the set of pressure readings at a first location (e.g., aorta) between 30 and 180 mmHg, a maximum pressure reading in the set of pressure readings at the first location between 40 and 200 mmHg, a minimum pressure reading in the set of pressure readings at a second location (distal) between -5 and 180 mmHg, a maximum pressure reading in the set of pressure readings at the second location between 10 and 200 mmHg, a pulse pressure corresponding to the set of pressure readings at the first location being at least 10 mmHg, a pulse pressure corresponding to the set of pressure readings at the second location being at least 10 mmHg, and a pulse pressure corresponding to the set of pressure readings at the first location being at least 10 mmHg. The pressure may be at least 5 mmHg, the maximum pressure measurement in the set of pressure measurements at the second location is less than 108% of the maximum pressure measurement in the set of pressure measurements at the first location, the minimum pressure measurement in the set of pressure measurements at the second location is less than 108% of the minimum pressure measurement in the set of pressure measurements at the first location, the heart rate over the first time period (e.g., as an average over the first time period) is between 40 and 300 beats per minute, and no heartbeat over the first time period varies by more than 30% from the average of every other heartbeat occurring during the first time period. Each of these conditions may be evaluated within the time period over which the pressure ratio is calculated, e.g., over the course of a period spanning two or more cardiac cycles.

[0122] In an example where the method 600 includes performing a pre-check, if one or more pre-check conditions are not met, then the method 600 may include rejecting the pressure measurement obtained at step 610 and performing step 610 again to obtain a new pressure measurement. This may be repeated until the pre-check at step 620 is met. As an example, if any one of the above pre-check conditions is not met, the method 600 may include rejecting and thus not using the pressure measurement obtained at step 610. In this example, if all of the above pre-check conditions are met, the method 600 may proceed to step 630 and use the pressure measurement obtained at step 610. Thus, determining whether the set of pressure measurements at the first location and the set of pressure measurements at the second location satisfy the set of pre-check conditions may include determining that each of the conditions comprising the set of pre-check conditions are satisfied. In some cases, the pre-check may be satisfied if fewer than all of the conditions comprising the set of pre-check conditions are satisfied.

[0123] At step 630, a pre-characteristic is identified. This step includes identifying two or more pre-characteristics. For example, this step may include identifying a first pre-characteristic associated with one or more pressure measurements in the set of pressure measurements at a first location, and a second pre-characteristic associated with one or more pressure measurements in the set of pressure measurements at a second location. In this step, the identified first pre-characteristic and / or the identified second pre-characteristic may be a characteristic type selected from a group of characteristic types consisting of a maximum pressure measurement, a minimum pressure measurement, a maximum decreasing pressure measurement rate of change, and a maximum increasing pressure measurement rate of change. In some further examples, the group of characteristic types from which the identified first pre-characteristic and / or the identified second pre-characteristic may be selected may also include a threshold decreasing pressure measurement rate of change.

[0124] In step 640, a post characteristic is identified. This step includes identifying two or more post characteristics. For example, this step may include identifying a first post characteristic associated with one or more pressure measurements in the set of pressure measurements at a first location and a second post characteristic associated with one or more pressure measurements in the set of pressure measurements at a second location. In this step, the identified first post characteristic and / or the identified second post characteristic may be a characteristic type selected from a group of characteristic types consisting of a maximum pressure measurement, a minimum pressure measurement, a maximum decreasing pressure measurement rate of change, and a maximum increasing pressure measurement rate of change. In some further examples, the group of characteristic types from which the identified first post characteristic and / or the identified second post characteristic may be selected may also include a threshold decreasing pressure measurement rate of change.

[0125] In method 600, the identified first posterior characteristic may follow the identified first pre-characteristic in the first time period, and the identified second posterior characteristic may follow the identified second pre-characteristic in the first time period. Further, at least one of the identified first pre-characteristic, the identified second pre-characteristic, the identified first posterior characteristic, and the identified second posterior characteristic may be associated with pressure measurements in the respective sets of pressure measurements at the first location and the second location that are taken at a time within the first time period that is different from a time within the first time period at which a dicrotic notch is present in the respective sets of pressure measurements at the first location and the second location.

[0126] At step 650, a pressure ratio is calculated. For example, at this step, the pressure ratio may be calculated using i) a pressure measurement in the set of pressure measurements at a first location between the identified first pre-characteristic and the identified first post-characteristic, and ii) a pressure measurement in the set of pressure measurements at a second location between the identified second pre-characteristic and the identified second post-characteristic. In other examples, at this step, the pressure ratio may be calculated using multiple pressure measurements between each identified pre-characteristic and post-characteristic. For example, the pressure ratio may be calculated using i) an average of a) one pressure measurement in the set of pressure measurements at a first location between the identified first pre-characteristic and the identified first post-characteristic, and b) another pressure measurement in the set of pressure measurements at a first location between the identified first pre-characteristic and the identified first post-characteristic, and ii) an average of a) one pressure measurement in the set of pressure measurements at a second location between the identified second pre-characteristic and the identified second post-characteristic, and b) another pressure measurement in the set of pressure measurements at a second location between the identified second pre-characteristic and the identified second post-characteristic.

[0127] Various examples have been described with reference to certain disclosed embodiments. The embodiments are presented for purposes of illustration and not limitation. Those skilled in the art will appreciate that various changes, adaptations, and modifications can be made without departing from the scope of the present invention.

Claims

[Claim 1] 1. A method of operation of a medical device having one or more processors for calculating a pressure ratio for assessing a vascular anatomy, comprising: the one or more processors acquiring a set of first location pressure measurements at a first location in a blood vessel over a first time period and a set of second location pressure measurements at a second location in a blood vessel over the first time period, where the first location is on a first side of a stenosis in the blood vessel and the second location is on a second side of the stenosis that is opposite the first location, and where the set of pressure measurements at the first location and the set of pressure measurements at the second location are not acquired during hyperemia. the one or more processors identifying a first pre-characteristic associated with one or more pressure measurements of the set of pressure measurements at the first location and a second pre-characteristic associated with one or more pressure measurements of the set of pressure measurements at the second location; the one or more processors identifying a first posterior characteristic associated with one or more pressure measurements in the set of pressure measurements at the first location and a second posterior characteristic associated with one or more pressure measurements in the set of pressure measurements at the second location, wherein: i) the identified first subsequent characteristic follows a first prior characteristic identified in the first time period, and the identified second subsequent characteristic follows a second prior characteristic identified in the first time period; ii) at least one of the identified first pre-characteristic, the identified second pre-characteristic, the identified first posterior characteristic, and the identified second posterior characteristic are associated with pressure measurements in the respective sets of pressure measurements at the first location and the second location that were taken without reference to any incision that may be present in the respective sets of pressure measurements at the first location and the second location; iii) each characteristic associated with said pressure measurements includes at least a maximum pressure measurement, a minimum pressure measurement, a maximum rate of change of a decreasing pressure measurement, or a maximum rate of change of an increasing pressure measurement within a respective pressure set; the one or more processors: i) a pressure measurement in the set of pressure measurements at the first location at a first time between the identified first pre-characteristic and the identified first post-characteristic; and ii) a pressure measurement in the set of pressure measurements at the second location at the first time between the identified second pre-characteristic and the identified second post-characteristic; calculating a pressure ratio between a pressure measurement at a first location and a pressure measurement at a second location at a first time using a pressure ratio function, wherein the first time is intermediate between a time of the identified first pre-characteristic and a time of the identified first post-characteristic and intermediate between a time of the identified second pre-characteristic and a time of the identified second post-characteristic. The method according to claim 1,

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