Patent Application
20140213890
This disclosure relates generally to techniques for gathering pressure measurements. More particularly, the disclosure relates to gathering bodily fluid dynamic pressure measurements.
Gathering pressure measurements in a body cavity is one of the tools of medical diagnosis and treatment. For example, intravascular and intracardiac hemodynamic measurements such as blood pressure measurements are performed frequently in catheterization suites to evaluate disease state severity as in the case of pulmonary hypertension, to guide therapy decisions as in the case of Fractional Flow Reserve (FFR) measurements to evaluate the degree of vascular stenosis and decide on the appropriate therapy, and/or to predict response to therapy and survival as in the case of cardiac resynchronization therapy in patients with heart failure.
Currently, intravascular and intracardiac pressure measurements are performed using either pressure wires which can suffer from measurement drifts and increased radiation exposure, or using non-invasive Doppler ultrasound which suffers from inaccuracies. A need exists to reduce radiation exposure, for example, by visualizing real-time location of tools on a short pre-recorded fluoroscopy image of the anatomy of interest. A desire also exists to improve accuracy in intravascular or intracardiac pressure measurements without additional radiation exposure.
According to one aspect, a method for gathering bodily fluid dynamic pressure measurements including placing a delivery tool in a region of interest (ROI), wherein the delivery tool comprises a sensor, wherein the sensor is positioned in a substantially perpendicular direction to a flow direction of the ROI; measuring a sensor displacement for a time period; and determining a pressure measurement in the ROI using the sensor displacement.
According to another aspect, a method for gathering bodily fluid dynamic pressure measurements including measuring a sensor displacement of an electromagnetic sensor positioned in a region of interest (ROI) for a time period, wherein the electromagnetic sensor is positioned in a substantially perpendicular direction to a flow direction of the ROI; and determining a pressure measurement in the ROI using the sensor displacement by: a) calculating a time-dependent acceleration, a, of the sensor according to x=x0+v0t+½ at2, where t is the time period, x is the sensor displacement, x0 is the initial sensor position at the beginning of the time period t, v0 is the initial sensor velocity at the beginning of the time period t; b) calculating a force F exerted on the sensor by a flow flowing in the flow direction according to F=ma, where a is the time-dependent acceleration of the sensor and m is the mass of the sensor; and c) calculating a pressure P exerted on the sensor according to the equation P=F/A, where F is force exerted on the sensor and A is the cross-sectional dimension of the sensor that is perpendicular to the flow direction.
According to yet another aspect, a device for gathering bodily fluid dynamic pressure measurements comprising a processor and a memory, the memory containing program code executable by the processor for performing the following: placing a delivery tool in a region of interest (ROI), wherein the delivery tool comprises a sensor, wherein the sensor is positioned in a substantially perpendicular direction to a flow direction of the ROI; measuring a sensor displacement for a time period; and determining a pressure measurement in the ROI using the sensor displacement.
Advantages of the present disclosure may include reducing radiation exposure, for example, by reducing the need for fluoroscopy, and reducing calibration drifts and/or measurement errors.
It is understood that other aspects will become readily apparent to those skilled in the art from the following detailed description, wherein it is shown and described various aspects by way of illustration. The drawings and detailed description are to be regarded as illustrative in nature and not as restrictive.
The detailed description set forth below in connection with the appended drawings is intended as a description of various aspects of the present disclosure and is not intended to represent the only aspects in which the present disclosure may be practiced. Each aspect described in this disclosure is provided merely as an example or illustration of the present disclosure, and should not necessarily be construed as preferred or advantageous over other aspects. The detailed description includes specific details for the purpose of providing a thorough understanding of the present disclosure. However, it will be apparent to those skilled in the art that the present disclosure may be practiced without these specific details. In some instances, well-known structures and devices are shown in block diagram form in order to avoid obscuring the concepts of the present disclosure. Acronyms and other descriptive terminology may be used merely for convenience and clarity and are not intended to limit the scope of the present disclosure.
In one aspect, the present disclosure relates to providing accurate positional information of a sensor located within the body of a patient. In one example, the sensor measures intravascular or intracardiac blood pressure. For example, the sensor is embedded, attached to or part of a delivery tool such as a catheter, a guidewire, a stylet or a lead. In one aspect, the delivery tool allows the positioning of the sensor such that it is positioned in a perpendicular direction to the direction of fluid flow. In one example, the fluid flow is blood flow. In another example, the fluid flow is spinal fluid flow or other bodily fluid flow. In yet another example, the fluid flow is air flow within the lungs. One skilled in the art would understand that the examples of fluid flow listed herein are just examples and that other types of fluid or air flow within a body cavity (e.g., a human body cavity), although not specifically mentioned herein, are part of the scope and spirit of the present disclosure.
In one example, with each heartbeat, the sensor moves according to the forces applied to it by the fluid flow (e.g., blood flow). The acceleration of the sensor is indicative of the pressures applied by the forces of the fluid flow.
In one aspect, given the position information measured by the sensor, the acceleration of the sensor may be calculated according to x=x0+v0t+½ at2 or any higher dimensional order or numerical variations where t is a time period, x is the sensor displacement, x0 is the initial sensor position at the beginning of the time period t, and v0 is the initial sensor velocity at the beginning of the time period t. In one example, v0 is zero because initially the sensor is not moving. Once the acceleration, a, is calculated and given the mass of the sensor m, Newton's second law F=ma and any higher order or numerical variations of it may be used to derive the total force F applied to the sensor. Given the perpendicular cross-section A of the sensor, pressure P applied to the sensor may be calculated according to P=F/A or any other higher order or numerical variations. Although specific equations are presented herein as examples, one skilled in the art would understand that other equations for calculating pressure, including more complex versions of the equations presented herein (e.g., higher dimensions, higher orders or numerical formats, etc.) are within the scope and spirit of the present disclosure.
In one example, the delivery tool is a catheter, a guidewire, a stylet or a lead. One skilled in the art would understand that the list of examples of delivery tools is not exclusive and that other delivery tools not listed herein may be used within the scope and spirit of the present disclosure.
In one example, the delivery tool has an “L” shape in one configuration. In this “L” shape, the delivery tool includes a tubular body and a tip where the tubular body makes up the longer portion of the “L” shape while the tip makes up the shorter portion of the “L” shape. The delivery tool includes an inserting configuration and a launched configuration. In the inserting configuration, the tip is a linear extension of the tubular body. In the launched configuration, the tip forms a substantially “L” shape with the tubular body. The tubular body may be hollow or it may be solid. The delivery tool may include a hinging component for configuring the delivery tool from the inserting configuration to the launched configuration. In one example, the hinging component is a hinge that couples the tubular body and the tip. In another example, one or more wire components are rotated to pivot the tip to form the L shape. The wire component(s) may be situated within the hollow tubular body of the delivery tool. In yet another example, the delivery tool includes shaped memory alloy such that the shape of the delivery tool is changed (for example, from an initial configuration to a launched configuration) when a particular temperature is reached, or when the delivery tool is in contact with a particular environment or experiences an environmental variable.
In one example, the sensor is housed at or near the tip of the delivery tool. The delivery tool may include a loaded spring for repositioning the sensor to an initial position following the sensor displacement from pressure of the fluid flow within the region of interest. The sensor may be an electromagnetic sensor or an ultrasonic sensor. However, one skilled in the art would understand that other types of sensors used for measuring displacement are also within the scope and spirit of the present disclosure.
In block 320, measure a sensor displacement for a time period. In block 330, determine a pressure measurement in the region of interest using the sensor displacement. In one aspect, the pressure measurement is determined by calculating a time-dependent acceleration of the sensor, calculating a force exerted on the sensor based on the time-dependent acceleration and calculating a pressure exerted on the sensor based on the force.
In another aspect, the pressure measurement is determined by performing the following: First, calculate a time-dependent acceleration, a, of the sensor according to the equation x=x0+v0t+½ at2 or any other higher order or numerical variations where t is the time period, x is the sensor displacement, x0 is the initial sensor position at the beginning of the time period t, and v0 is the initial sensor velocity at the beginning of the time period t. In one example, v0 is zero because initially the sensor is not moving. Second, calculate a force F exerted on the sensor by a flow flowing in the flow direction according to the equation F=ma or any other higher order or numerical variations, where a is the time-dependent acceleration of the sensor and m is the mass of the sensor. Third, calculate a pressure P exerted on the sensor according to the equation P=F/A or any other higher order or numerical variations, where F is force exerted on the sensor and A is the cross-sectional dimension of the sensor that is perpendicular to the flow direction. In one example, the mass and area of the tip of the delivery tool where the sensor is positioned are negligible compared to the mass and area of the sensor. In another example, the mass and area values used in the calculation may take the mass and area of the tip into account if they are not deemed to be negligible. In another example where the delivery tool includes a loaded spring at or near the tip, the mass of the loaded spring may be included as part of the sensor mass in the calculation. One skilled in the art would understand that the value of the mass m in the calculation may include any other mass value associated with the delivery tool that is needed to be included so to provide an accurate measurement based on the equations described herein.
In yet another aspect, the pressure measurement is determined by performing the following: First, calculate a force F exerted on the sensor by a flow in the flow direction according to the equation F=kx or any other higher order or numerical variations, where k is an effective spring constant of the sensor and x is the sensor displacement. Second, calculate a pressure P exerted on the sensor according to the equation P=F/A or any other higher order or numerical variations, where F is the force exerted on the sensor and A is the cross-sectional dimension of the sensor that is perpendicular to the flow direction.
In one example, the value of the effective spring constant of the sensor k is unknown, however, the ratio of k/m is known where m is the mass of the sensor. However, one skilled in the art would understand that if the mass of the tip of the delivery tool and/or the mass of a loaded spring at or near the tip are not negligible, the value of m as used in the calculation may include the mass of the tip and/or the mass of the loaded spring. And, one skilled in the art would also understand that the value of the mass m in the calculation may include any other mass value associated with the delivery tool that is needed to be included so as to provide an accurate measurement based on the equations described herein.
In this example, the pressure measurement is determined by performing the following: First, calculate a time-dependent acceleration, a, of the sensor according to the equation a=(k/m)*x or any higher order or numerical variations, where k is a spring constant of the sensor, m is the mass of the sensor and x is the sensor displacement. Second, calculate a force F exerted on the sensor by a flow flowing in the flow direction according to the equation F=ma or any higher order or numerical variations, where m is the mass of the sensor and a is the time-dependent acceleration of the sensor. Third, calculate a pressure P exerted on the sensor according to the equation P=F/A or any higher order or numerical variations, where F is force exerted on the sensor and A is the cross-sectional dimension of the sensor that is perpendicular to the flow direction.
In one example, the steps illustrated in
In one aspect, the region of interest (ROI) is an artery or a vein, for example, a coronary artery or a cardiac vein. In one example, the region of interest (ROI) is a cardiac chamber, for example, in the ventricles or atria. In another example, the ROI is a cerebral spinal fluid cavity. In another example, the ROI is the trachea, the bronchia or the lung cavity. One skilled in the art would understand that the list of examples of ROI is not exclusive and that the present disclosure may be equally applicable to other bodily cavities. In one example, the time period t is related to a cardiac cycle. However, depending on the ROI, the time period t may be related, for example, to a respiratory cycle or another bodily cycle.
While for purposes of simplicity of explanation, the methodologies are shown and described as a series of acts, it is to be understood and appreciated that the methodologies are not limited by the order of acts, as some acts may, in accordance with one or more aspects, occur in different orders and/or concurrently with other acts from that shown and described herein. For example, those skilled in the art will understand and appreciate that a methodology could alternatively be represented as a series of interrelated states or events. Moreover, not all illustrated acts may be required to implement a methodology in accordance with one or more aspects.
The previous description of the disclosed aspects is provided to enable any person skilled in the art to make or use the present disclosure. Various modifications to these aspects will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other aspects without departing from the spirit or scope of the disclosure.
