End-expiratory detection using impedance measurements

Abstract

The subject matter of the invention is end-expiratory detection using impedance measurements. The present disclosure provides a method that includes measuring body impedance as a function of time using a plurality of electrodes attached to a patient. A total impedance value is calculated as a function of time from the measured impedance. A temporal minimum of the total impedance value is associated with a timing of end expiration of the patient.

Description

Technical Field

[0001] The present disclosure generally relates to the detection of respiratory effects and, in particular, to detecting the end of expiration. Background Art

[0002] Techniques for compensating for respiratory effects have been previously reported in the patent literature. For example, U.S. Patent 10,524,692 describes a method that includes positioning body electrodes in electrical contact with a patient's body and positioning a probe within the patient's body. The method further includes tracking the position of the probe during the patient's respiration and determining an indication related to the impedance between the body electrodes during respiration. The method further includes calculating a function that correlates the position of the probe with the indication and applying the function to identify the end-expiration point of respiration based on subsequent indications related to the impedance.

[0003] The present disclosure will be more fully understood from the following detailed description of embodiments of the disclosure in conjunction with the accompanying drawings, in which: Brief Description of the Drawings

[0004] Figure 1 is a schematic illustration of a catheter-based electroanatomical (EA) mapping and ablation system according to an example of the present disclosure;

[0005] Figure 2 is a schematic illustration of the layout and circuitry of an electrical measurement device for end-expiration detection according to an example of the present disclosure;

[0006] Figure 3 is a graph of the total impedance R(t) of an actual patient undergoing cardiac ablation according to an example of the present disclosure; and

[0007] Figure 4 is a flowchart schematically illustrating a method and algorithm for electrically detecting end-expiration according to an example of the present disclosure. Detailed Description

[0008] Overview

[0009] A wide range of medical procedures involve the use of invasive probes, such as cardiac catheters, to diagnose and / or treat patients. The quality of a medical application may depend on the detection of the end of the expiratory portion of the respiratory cycle (referred to herein as "end-expiration"). For example, it is desirable to time the occurrence of a medical procedure at end-expiration due to the relaxation of internal movements. For example, applying cardiac ablation during end-expiration may be safer and more accurate.

[0010] During a respiratory cycle, the measured electrical impedance of the body tends to be affected by the lungs alternately filling with air and then emptying the air, as air is an insulator. Examples of the present disclosure described herein provide a technique for tracking a whole body impedance indication that is calculated based on conductivity measured using patch electrodes attached to the skin of a patient's torso (e.g., at the back and chest regions). It has been found that the disclosed whole body impedance indication has a close correlation with the lungs that are emptied of air at the end of exhalation. In some examples, the disclosed technique uses a plurality of patch electrodes attached to the patient's skin to measure a combined impedance matrix ρ or a combined conductivity matrix σ, which respectively describe the combined impedance or conductivity of the patch electrodes and the corresponding impedance or conductivity of the patient's body.

[0011] The patch electrodes used can be the patch electrodes of an already in-place electrical tracking system (e.g., for tracking the positioning of a catheter within the heart). In this case, each patch acts as a transmitter of an AC signal at a unique frequency, while the other patches act as receivers. In this way, the system can receive multiple AC signals, and based on these signals, a processor can calculate the combined impedance matrix ρ or the conductivity matrix σ.

[0012] Examples of a method and technique for obtaining the combined conductivity matrix σ are described in U.S. Patent Nos. 8,456,182 and 10,524,692, both of which are assigned to the assignee of the present application. The inventors note that the parameter that best describes the impedance of the subject's torso is the sum of the patch-to-patch conductivities across all patches. This sum can be obtained by calculating the diagonal sum (e.g., the matrix trace) of the conductivity matrix σ.

[0013] To this end, in some examples, the processor uses the value of the reciprocal of the trace of the matrix σ, R(t) = 1 / Tr(σ), where t is time. The time during which the lungs are emptied of air the most (i.e., at the end of exhalation) during a corresponding respiratory cycle appears as the minimum of the time-dependent total impedance function R(t).

[0014] The processor can output the timing of the end of exhalation to the user as an algorithm (e.g., by marking the minimum value and outputting the mark to a cardiac ablation algorithm). Alternatively or additionally, the processor can output the timing of the end of exhalation by displaying the curve R(t) on a display device.

[0015] It has been found that the disclosed end-of-exhalation detection technique is accurate and robust in cardiac ablation and in services for other electrically noisy phenomena during invasive and non-invasive treatments that require end-of-exhalation detection. Generally, the disclosed technique can be applied as described below with a stand-alone processor or with the processor of any medical system that needs to use the technique (e.g., a medical imaging system that requires respiratory gating).

[0016] System Description

[0017] Figure 1 is a schematic illustration of a catheter-based electroanatomical (EA) mapping and ablation system 10 according to an example of the present disclosure.

[0018] System 10 includes a plurality of catheters that are percutaneously inserted by a physician 24 through a patient's vascular system into a chamber or vascular structure of the heart 12 (as seen in inset 45). Generally, a delivery sheath catheter is inserted into a heart chamber (such as the left atrium or right atrium) near a desired location in the heart 12. Subsequently, a plurality of catheters are inserted into the delivery sheath catheter to reach the desired location. The plurality of catheters can include a catheter dedicated to pacing, a catheter for sensing intracardiac electrogram signals, a catheter dedicated to ablation, and / or a catheter dedicated to both EA mapping and ablation. The exemplary catheter 14 shown herein is configured for sensing bipolar electrograms. The physician 24 places the distal end 28 of the catheter 14 (also hereinafter referred to as the distal end assembly 28) in contact with the heart wall for sensing a target site in the heart 12. For ablation, the physician 24 similarly brings the distal end of the ablation catheter to the target site.

[0019] As shown in inset 65, catheter 14 is an exemplary catheter including a basket-shaped distal end 28 that includes one, preferably a plurality of electrodes 26, which are optionally distributed on a plurality of splines 22 at the distal end 28 and are configured to sense IEGM signals. Catheter 14 may additionally include a positioning sensor 29 embedded in or near the distal end 28 on the shaft 46 of the catheter 14 for tracking the position and orientation of the distal end 28. Optionally and preferably, the positioning sensor 29 is a magnetic-based positioning sensor that includes three magnetic coils for sensing three-dimensional (3D) position and orientation. As shown, the distal end 28 also includes an expansion / collapse rod 42 of the expandable assembly 28 that is mechanically connected to the basket assembly 28 at the distal edge 41 of the assembly 28.

[0020] The magnetic-based positioning sensor 29 can operate in conjunction with a position pad 25 that includes a plurality of magnetic coils 32 configured to generate a magnetic field in a predefined workspace. The real-time position of the distal end 28 of the catheter 14 can be tracked based on the magnetic field generated by the position pad 25 and sensed by the magnetic-based positioning sensor 29. Details of magnetic-based position sensing techniques are described in U.S. Pat. Nos. 5,391,199, 5,443,489, 5,558,091, 6,172,499, 6,239,724, 6,332,089, 6,484,118, 6,618,612, 6,690,963, 6,788,967, 6,892,091.

[0021] System 10 includes one or more electrode patches 38 that are positioned in contact with the skin of patient 23 to establish a position reference for position pad 25 and impedance-based tracking of electrodes 26. For impedance-based tracking, current is directed toward electrodes 26 and sensed at the electrode skin patches 38 such that the position of each electrode can be triangulated via the electrode patches 38. Details of impedance-based position tracking techniques are described in U.S. Patent Nos. 7,536,218, 7,756,576, 7,848,787, 7,869,865, 8,456,182, and 10,524,692.

[0022] The electrode patches 38 can be used in an independent manner with a processor running the disclosed algorithms to electrically detect end-expiration, as Figures 2 to 4 described. This detection is used to improve the results of ablation using a probe such as catheter 14, but the detection itself does not depend on the presence of a probe within the patient. In the disclosed example, physician 24 can select / deselect and / or view the results of the disclosed end-expiration detection algorithm, for example, via a graphical user interface (GUI) 111.

[0023] Recorder 11 displays on display device 27 the cardiac signals 21 (e.g., electrograms acquired at separately tracked cardiac tissue locations) acquired using the body surface ECG electrodes 18 and intracardiac electrograms acquired using the electrodes 26 of catheter 14. Recorder 11 can include pacing capabilities for pacing the heart rhythm and / or can be electrically connected to an independent pacemaker.

[0024] Workstation 55 includes a memory 57, a processor 56 unit with a memory or storage device having appropriate operating software loaded therein, and user interface capabilities. Workstation 55 can provide a plurality of functions, optionally including: (i) performing three-dimensional (3D) modeling of the endocardial anatomy and rendering a model or EA map 20 for display on display device 27; (ii) displaying on display device 27, as representative visual markers or images superimposed on the rendered EA map 20, the activation sequence (or other data) compiled from the recorded cardiac signals 21; (iii) displaying the real-time position and orientation of multiple catheters within the cardiac chamber; and (iv) displaying on display device 27 relevant sites, such as where ablation energy has been applied. A commercial product embodying the elements of system 10 can be CARTO TM 3System, which is available from Biosense Webster, Inc., 31A Technology Drive, Irvine, CA 92618.

[0025] System 10 may include an ablation energy generator 50 that is adapted to conduct ablation energy to one or more electrodes at the distal end of a catheter configured for ablation. The energy generated by ablation energy generator 50 may include, but is not limited to, radio frequency (RF) energy or pulsed field ablation (PFA) energy (including unipolar or bipolar high voltage DC pulses to be used to effect irreversible electroporation (IRE)), or a combination thereof.

[0026] The patient interface unit (PIU) 30 is an interface configured to establish electrical communication between the catheter, electrophysiology equipment, power supply, and workstation 55 to control the operation of System 10 and to receive EA signals from the catheter. The electrophysiology equipment of System 10 may include, for example, a plurality of catheters, position pads 25, body surface ECG electrodes 18, electrode patches 38, ablation energy generator 50, and recorder 11. Optionally and preferably, PIU 30 further includes processing capabilities for performing real-time calculation of catheter position and for performing ECG calculations.

[0027] In some embodiments, processor 56 generally includes a general-purpose computer that is programmed in software to perform the functions described herein. The software may be downloaded electronically to the computer via a network, for example, or alternatively or additionally it may be set up and / or stored on a non-transitory tangible medium (such as magnetic memory, optical memory, or electronic memory).

[0028] This configuration of System 10 is shown by way of example in order to illustrate certain problems solved by examples of the present disclosure and to demonstrate the application of these examples in enhancing the performance of such a system. However, embodiments of the present disclosure are in no way limited to this particular class of exemplary systems, and the principles described herein may be similarly applied to other types of medical systems. For example, other multi-electrode catheter types, such as multi-arm OCTARAY TM catheters or flat catheters, may be used.

[0029] Although the disclosed technology is described using Figure 1 it may be described using the following Figure 2 in conjunction with a stand-alone processor and has nothing to do with Figure 1 Therefore, the disclosed technology may be applied as described in Figure 2 and Figure 3 in conjunction with a stand-alone processor or with the processor of any medical system that requires the use of the technology (e.g., a medical imaging system that requires respiratory gating).

[0030] Electrical measuring device for detecting end-expiration

[0031] Figure 2Schematic illustration of the layout and circuitry of an electrical measurement device 200 for detecting the end of exhalation, according to an example of the present disclosure. The device 200 is seen in two states: (a) the start of exhalation and (b) the end of exhalation. The difference between these two states is the amount of air in the lungs, which is schematically illustrated by a first side view 202 of the torso seen at the start of exhalation and a second side view 222 of the torso seen at the end of exhalation. As further seen, the device 200 uses six patch electrodes 206, three of which are attached to the skin at the back of the patient's torso (202, 222), and three of which are attached to the skin at the chest.

[0032] An AC signal source 208 applies an AC signal between each respective patch electrode 206 and a common ground 214. An AC signal meter 210 measures the AC signal generated between each of the patch electrodes 206 and the common ground 214. The AC signal generator sources 208 each transmit at a unique frequency f j The varying impedance of the body due to breathing affects the measured AC signal (209) received at the remaining patch 206.

[0033] Using the AC signal measured by the AC signal meter 210, Figure 1 a processor 56 applies an electrical model to calculate the above matrix σ, which, Figure 2 in this case, is a 6×6 matrix. Figure 3 An example of deriving a total impedance value by the processor 56 from σ is shown, where the total impedance value is the reciprocal of the trace of the matrix σ, R(t) = 1 / Tr(σ), where t is time.

[0034] Electrical detection of end-expiration

[0035] Figure 3 Graph 300 of the total impedance R(t) 333 of an actual patient undergoing cardiac ablation, according to an example of the present disclosure. The total impedance 333 is shown along a reference method graph (334) for measuring the end of exhalation electrically, which total impedance is derived using the method of U.S. Patent 10,524,692 and serves as a validation reference. As seen, there is good agreement between the graphs regarding the timing of the impedance minimum 302.

[0036] One possible reason for considering using the disclosed method (e.g., graph 333) in cardiac ablation, as compared to the method of U.S. Patent 10,524,692, is the simplicity of the method. Another possible reason for considering using the disclosed method in cardiac ablation is that graph 333 shows that the disclosed method is less affected by the high voltage or current signals applied during cardiac ablation in the time window (shown as "1" in curve 335).

[0037] Method for detecting end-expiration using body impedance

[0038] Figure 4 is a flowchart schematically illustrating a method and an algorithm for electrically detecting end - expiration according to an example of the present disclosure. According to this embodiment, the algorithm performs a process that starts with a conductivity measurement step 402, measuring the conductivity of a patient's body by using the disclosed technique involving patch electrodes, as implemented, for example, as shown in the example of Figure 2 .

[0039] Next, at a total conductivity calculation step 404, the processor uses the measured conductivity to calculate a total conductivity value, such as Tr(σ). Next, at a total impedance calculation step 406, the processor derives a measure of the total impedance, such as 1 / Tr(σ). For clarity of the illustrative method, steps 404 and 406 are shown in excessive detail, but in other examples these steps may be simplified to a single step.

[0040] At a minimum - value correlation step 408, the processor correlates the minimum value 1 / Tr(σ) with the timing of end - expiration, for example, by marking the minimum value for use in cardiac ablation.

[0041] Finally, at an output step 410, the processor outputs the timing of end - expiration as an algorithm (e.g., a cardiac ablation algorithm). The processor outputs the timing of end - expiration by displaying a curve 333 on a display device 27.

[0042] Figure 4 The example flowchart shown in

[0043] Examples

[0044] Example 1

[0045] is chosen solely for conceptual clarity. This example may also include additional steps of the algorithm, such as obtaining an electrocardiogram, which have been intentionally omitted from the present disclosure to provide a simplified flowchart.

[0046] Example 2

[0047] A method, the method comprising: measuring body impedance as a function of time using a plurality of electrodes (38) attached to a patient (23); calculating a total impedance value as a function of time based on the measured impedance; correlating a time minimum of the total impedance value with the timing of end - expiration of the patient; and outputting the timing of end - expiration to a user.

[0048] Example 3

[0049] The method according to any one of Embodiments 1 and 2, wherein calculating the total impedance value includes calculating the reciprocal of the trace of the conductivity matrix σ.

[0050] Example 4

[0051] The method according to any one of Embodiments 1 to 3, and the method includes: applying a medical procedure to the patient (23) in a time window before and after the timing at the end of exhalation.

[0052] Example 5

[0053] The method according to any one of Embodiments 1 to 4, wherein the medical procedure includes cardiac ablation.

[0054] Example 6

[0055] The method according to any one of Embodiments 1 to 5, wherein outputting the timing includes outputting the timing to a cardiac ablation algorithm.

[0056] Example 7

[0057] The method according to any one of Embodiments 1 to 5, wherein outputting the timing includes displaying the timing on a display device (27).

[0058] Example 8

[0059] A system (10), the system includes: a circuit (200) and a processor (56). The circuit (200) is configured to measure body impedance as a function of time using a plurality of electrodes (38, 206) attached to a patient (23). The processor (56) is configured to: (i) calculate a total impedance value as a function of time based on the measured impedance; (ii) associate the time minimum value of the total impedance value with the timing at the end of exhalation of the patient; and (iii) output the timing at the end of exhalation to a user.

[0060] Although the embodiments described herein are mainly directed to cardiac diagnostic applications, the methods and systems described herein can also be used in other medical applications.

[0061] It should be understood that the above embodiments are cited by way of example, and the present disclosure is not limited to what is specifically shown and described above. On the contrary, the scope of the present disclosure includes combinations and sub - combinations of the various features described above and their variations and modifications, which variations and modifications will occur to those skilled in the art upon reading the above description and which are not disclosed in the prior art.

Claims

1. A method, comprising: measuring the impedance of the body as a function of time using a plurality of electrodes attached to the patient; calculating a total impedance value as a function of time based on the measured impedance; correlating a temporal minimum of the total impedance value to a timing of end-expiration of the patient; as well as The timing of end-tidal exhalation is output.

2. The method according to claim 1, wherein: The plurality of electrodes include electrodes of an electrolocalization tracking system.

3. The method according to claim 1, wherein: Calculating the total impedance value includes calculating the inverse of the trace of the conductivity matrix.

4. The method according to claim 1, and comprising: A medical procedure is applied to the patient at a time window before and after the timing of end-tidal exhalation.

5. The method according to claim 4, wherein: The medical procedure includes cardiac ablation.

6. The method according to claim 1, wherein: Outputting the timing includes outputting the timing to a cardiac ablation algorithm.

7. The method according to claim 1, wherein: Outputting the timing includes displaying the timing on a display device.

8. A system, comprising: a circuit configured to measure impedance of the body as a function of time using a plurality of electrodes attached to the patient; and A processor, the processor being configured to: calculating a total impedance value as a function of time based on the measured impedance; correlating a temporal minimum of the total impedance value to a timing of end-expiration of the patient; as well as The timing of end-expiration is output to the user.

9. The system according to claim 8, wherein: The plurality of electrodes include electrodes of an electrolocalization tracking system.

10. The system according to claim 8, wherein: The processor is configured to calculate the total impedance value by calculating the inverse of the trace of the conductivity matrix.

11. The system according to claim 8, wherein: The processor is further configured to apply a medical protocol to the patient at a time window before and after the timing of end-tidal exhalation.

12. The system according to claim 10, wherein: The medical procedure includes cardiac ablation.

13. The system according to claim 8, wherein: The processor is configured to output the timing by outputting the timing to a cardiac ablation algorithm.

14. The system according to claim 8, wherein: The processor is configured to output the timing by displaying the timing on a display device.

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