End-expiration detection using impedance measurements

Abstract

To provide the end-expiratory time.SOLUTION: A method includes measuring impedances of a body using a plurality of electrodes attached to a patient, as a function of time. A total impedance value is calculated from the measured impedances, as a function of time. Temporal minima of the total impedance value are associated with timings of end-expiration of the patient.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure generally relates to the detection of the impact on breathing, and specifically to the detection of the end-expiratory time.

Background Art

[0002] Techniques for compensating for the impact on a respirator have been previously reported in patent literature. For example, U.S. Patent No. 10,524,692 describes a method including positioning body electrodes by making galvanic contact with a patient's body and identifying the location of a probe within the patient's body. This method further includes tracking the position of the probe during the patient's breathing and determining an index associated with the impedance between the body electrodes during breathing. This method also includes calculating a function that associates the position of the probe with the index and applying that function to identify the end-expiratory point of breathing based on a subsequent index associated with the impedance.

[0003] A more complete understanding of the present disclosure will be obtained by reading the following detailed description of the embodiments of the present disclosure in conjunction with the drawings.

Brief Description of the Drawings

[0004]

Figure 1

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Modes for Carrying Out the Invention

[0005] Summary 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 medical applications may depend on the detection of the end of the exhalation portion of the respiratory cycle (referred to herein as "end-expiration"). For example, due to the relaxation of internal movements, it is desirable for the timing of the medical procedure to occur at end-expiration. For example, applying cardiac ablation during end-expiration can be safer and more accurate.

[0006] During the respiratory cycle, since air is an insulator, the measured electrical impedance of the body tends to be affected as the lungs are alternately filled with air and then emptied. Embodiments of the present disclosure described herein provide techniques for tracking a total body impedance metric calculated from conductivity measured using patch electrodes attached to the skin of a patient's torso (e.g., the back and chest regions). The disclosed total body impedance metric has been found to correlate well with lungs emptied of air at end-expiration. In some embodiments, the disclosed techniques utilize several patch electrodes attached to a patient's skin to measure a synthetic impedance matrix ρ or a synthetic conductivity matrix σ, which represent the synthetic impedance or conductivity of the patch electrodes and the respective impedance or conductivity of the patient's body, respectively.

[0007] The patch electrodes used can be the patch electrodes of an electrical tracking system that is already in a predetermined position (e.g., to track the position of a catheter within the heart). In such cases, each patch functions as a transmitter of an AC signal at a unique frequency, and the other patches function as receivers. In this way, the system can receive a plurality of AC signals, and based on these signals, a processor can calculate the synthetic impedance or conductivity matrix, ρ or σ.

[0008] Examples of methods and techniques for obtaining the synthetic 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 have noted that the parameter that best describes the torso impedance of a subject is the sum of the conductivities between patches over all patches. This sum can be obtained by calculating the diagonal sum (e.g., matrix trace) of the conductivity matrix σ.

[0009] For this purpose, in some embodiments, the processor uses the value of the reciprocal of the trace of matrix σ, R(t) = 1 / Tr(σ), where t is time. The time during each respiratory cycle when the lungs are most empty (i.e., end - expiration) is represented as the minimum value of the time - dependent total impedance function R(t).

[0010] The processor can output to the user the timing of end - expiration as an algorithm (e.g., by tagging the minimum value and outputting the tag to a cardiac ablation algorithm). Alternatively or additionally, the processor can output the timing of end - expiration by displaying the curve R(t) on a display device.

[0011] The disclosed end - expiration detection technique has been found to be accurate and robust in cardiac ablation services and in other electrical - noise - induction phenomena during invasive and non - invasive treatments that require end - expiration detection. Generally, the disclosed technique can be applied with a stand - alone processor or with the processor of any medical system that requires the use of the technique (e.g., a medical imaging system that requires respiratory gating), as described below.

[0012] Description of the System FIG. 1 is a schematic depiction of a catheter - based electrophysiological (EA) mapping and ablation system 10 according to an embodiment of the present disclosure.

[0013] System 10 includes a plurality of catheters (see insertion figure 45) that are percutaneously inserted by physician 24 into a chamber of heart 12 or a vascular structure through a patient's vasculature. Typically, a delivery sheath catheter is inserted into a heart chamber, such as the left or right atrium, near a desired location within heart 12. Thereafter, 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 illustrated herein is configured to sense a bipolar electrogram. Physician 24 contacts the distal tip 28 (hereinafter also referred to as distal end assembly 28) of catheter 14 with the heart wall to sense a target site of heart 12. For ablation, physician 24 similarly brings the distal end of the ablation catheter to the target site.

[0014] As seen in insertion figure 65, catheter 14 is an exemplary catheter that includes a basket-shaped distal end 28 that optionally includes one, preferably a plurality of electrodes 26 distributed across a plurality of splines 22 at distal tip 28 and configured to sense IEGM signals. Catheter 14 can further include a position sensor 29 embedded within or near distal tip 28 on shaft 46 of catheter 14 to track the position and orientation of distal tip 28. Optionally and preferably, position sensor 29 is a magnetic-based position sensor that includes three magnetic coils for sensing three-dimensional (3D) position and orientation. As seen, distal tip 28 further includes a deployable / foldable rod 42 of an expandable assembly 28 that is mechanically connected to basket assembly 28 at the distal edge 41 of assembly 28.

[0015] The magnetic-based position sensor 29 can be operated with a position pad 25 that includes a plurality of magnetic coils 32 configured to generate a magnetic field within a predetermined working volume. The real-time position of the distal tip 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 position sensor 29. Details of the magnetic-based position sensing technique are described in U.S. Patent 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, and 6,892,091.

[0016] The system 10 includes one or more electrode patches 38 disposed for skin contact with the patient 23 to establish a position reference for the position pad 25 and impedance-based tracking of the electrodes 26. For impedance-based tracking, a current is directed to the electrodes 26 and sensed at the electrode skin patches 38, whereby the position of each electrode can be triangulated via the electrode patches 38. Details of the impedance-based position tracking technique 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.

[0017] The electrode patch 38 can be used in a stand-alone manner with a processor that executes the disclosed algorithm to electrically detect the end of expiration, as described in FIGS. 2-4. This detection is used to improve the outcome of ablation using a probe such as the catheter 14, but the detection itself does not depend on the presence of a probe within the patient's body. In the disclosed embodiment, the physician 24 may select / deselect and / or observe the results of the disclosed end-expiration detection algorithm, for example, via a graphical user interface (GUI) 111.

[0018] Recorder 11 displays on display device 27 the cardiac signal 21 (e.g., an electrocardiogram obtained at the position of each tracked cardiac tissue) acquired using body surface ECG electrodes 18 and the intracardiac electrocardiogram acquired using electrodes 26 of catheter 14. Recorder 11 may include pacing capabilities for pacing the rhythm of the heart and / or may be electrically connected to an independent pacemaker.

[0019] Workstation 55 includes a memory 57, a processor 56 unit having a memory or storage device loaded with appropriate operating software, and user interface functions. Workstation 55 optionally provides a plurality of functions including: (i) modeling the endocardial anatomical structure in three dimensions (3D) and rendering it for display on display device 27 as a model or EA map 20; (ii) displaying on display device 27 a representative visual display or image of the excitation sequence (or other data) compiled from the recorded cardiac signal 21 superimposed on the rendered EA map 20; (iii) displaying the real-time position and orientation of a plurality of catheters within the heart chamber; and (iv) displaying on display device 27 regions of interest such as the location where ablation energy was applied. One commercially available product embodying the elements of system 10 is available as the CARTO (trademark) 3 system, obtainable from Biosense Webster, Inc., 31A Technology Drive, Irvine, CA, 92618.

[0020] System 10 may include an ablation energy generator 50 adapted to deliver ablation energy to one or more electrodes at the distal tip of a catheter configured for ablation. The energy generated by ablation energy generator 50 may include radiofrequency (RF) energy, pulsed-field ablation (PFA) energy, or a combination thereof, including but not limited to monopolar or bipolar high voltage DC pulses used to effect irreversible electroporation (IRE).

[0021] Patient interface unit (PIU) 30 is an interface configured to establish electrical communication between the catheter, electrophysiological equipment, power supply, and workstation 55 to control the operation of system 10 and to receive EA signals from the catheter. The electrophysiological 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 additionally includes processing capabilities for performing real-time calculations of catheter position and for performing ECG calculations.

[0022] In some embodiments, processor 56 typically includes a general-purpose computer programmed in software to perform the functions described herein. The software may be downloaded to the computer in electronic form, for example, via a network, or alternatively or additionally, may be provided and / or stored on a non-transitory tangible medium such as magnetic memory, optical memory, or electronic memory.

[0023] This configuration of system 10 is shown as an example to illustrate the particular problems addressed by embodiments of the present disclosure and to demonstrate the application of these embodiments in improving the performance of such a system. However, embodiments of the present disclosure are in no way limited to this particular type of exemplary system, and the principles described herein may equally apply to other types of medical systems. For example, other multi-electrode catheter types such as the multi-arm OCTARAY (trademark) catheter or flat catheter may be used.

[0024] The disclosed technology has been described using FIG. 1, but this technology can be described using FIG. 2 below with a stand-alone processor, regardless of FIG. 1. Thus, the disclosed technology can be applied with a stand-alone processor or with the processor of any medical system (e.g., a medical imaging system that requires respiratory gating) that requires the use of that technology, as described in FIGS. 2 and 3.

[0025] Electrical measuring device for detecting end-expiration FIG. 2 is a schematic depiction of the layout and circuitry of an electrical measuring device 200 used to detect end-expiration, according to an embodiment of the present disclosure. The device 200 is seen in two states: (a) the start of expiration and (b) the end of expiration. The difference between these two states is the amount of air inside the lungs, which is schematically shown by a first side view 202 of the torso seen at the start of expiration and a second side view 222 of the torso seen at the end of expiration. Further seen, there are six patch electrodes 206 in the use by the device 200, three of which are attached to the skin behind the patient's torso (202, 222) and three are attached to the skin of the chest.

[0026] The AC signal source 208 applies an AC signal between each respective patch electrode 206 and the common ground 214. The AC signal meter 210 measures the resulting AC signal between each of the patch electrodes 206 and the common ground 214. Each of the AC signal sources 208 has a unique frequency f jIt is transmitted. The changing impedance of the body due to breathing affects the measured AC signal received (209) at the remaining portion of the patch 206.

[0027] Using the AC signal measured by the meter 210, the processor 56 of FIG. 1 applies an electrical model to calculate the above-mentioned matrix σ (which is a 6×6 matrix in the case of FIG. 2). An example of the total impedance value derived from σ, where the processor 56 is the reciprocal of the trace of the matrix σ, R(t)=1 / Tr(σ) (where t is time), is shown in FIG. 3.

[0028] Electrical Detection of End-Expiration FIG. 3 is a graph 300 of the total impedance R(t) 333 of an actual patient undergoing cardiac ablation according to an embodiment of the present disclosure. The total impedance 333 is derived using the method of U.S. Patent No. 10,524,692 and is shown along a graph (334) of a reference method for electrically measuring end-expiration that functions as a verification criterion. As shown, there is a good agreement between the graphs regarding the timing of the minimum value 302 of the impedance.

[0029] One possible reason for considering using the method disclosed in cardiac ablation (e.g., graph 333) is its simplicity compared to the method of U.S. Patent No. 10,524,692. Another possible reason for considering using the method disclosed in cardiac ablation is that graph 333 shows that the method disclosed is not overly affected by the high voltage or current signal applied during the time window (shown as "1" in curve 335) of cardiac ablation.

[0030] Method for Detecting End-Expiration Using Body Impedance Figure 4 is a flowchart schematically showing a method and an algorithm for electrically detecting the end of exhalation according to an embodiment of the present disclosure. According to this embodiment, the algorithm starts with a conductivity measurement step 402 by measuring the conductivity of a patient's body using the disclosed technique with patch electrodes, as implemented and shown by way of example in Figure 2.

[0031] Next, in a total conductivity calculation step 404, the processor calculates a total conductivity value such as Tr(σ) using the measured conductivity. Next, in a total impedance calculation step 406, the processor derives a measured value of the total impedance such as 1 / Tr(σ). Steps 404 and 406 are described in some excess detail for the sake of clarity of the illustrated method, but these steps may be reduced to a single step in other examples.

[0032] In a minimum value association step 408, the processor can associate the minimum value of 1 / Tr(σ) with the timing of the end of exhalation, for example, by tagging the minimum value for use in cardiac ablation.

[0033] Finally, in an output step 410, the processor outputs the timing of the end of exhalation as an algorithm (e.g., a cardiac ablation algorithm). The processor outputs the timing of the end of exhalation by displaying curve 333 on display device 27.

[0034] The exemplary flowchart shown in Figure 4 is selected purely for the purpose of clarifying the concept. This embodiment also includes additional steps of the algorithm, such as obtaining an electrocardiogram, which are intentionally omitted from the disclosure herein to provide a more simplified flowchart.

Example

[0035] (Example 1) The method includes measuring the impedance of the body as a function of time using a plurality of electrodes (38) attached to a patient (23). A total impedance value is calculated as a function of time from the measured impedance. The temporal minimum value of the total impedance value is associated with the timing of the end of exhalation of the patient. The timing of the end of exhalation is output to the user.

[0036] (Example 2) The method according to Example 1, wherein the plurality of electrodes (38) includes the electrodes of the electrical position tracking system (10).

[0037] (Example 3) The method according to any one of Examples 1 and 2, wherein calculating the total impedance value includes calculating the reciprocal of the trace of the conductivity matrix σ.

[0038] (Example 4) The method according to any one of Examples 1 to 3, including applying a medical treatment to the patient (23) within a time window around the timing of the end of exhalation.

[0039] (Example 5) The method according to any one of Examples 1 to 4, wherein the medical treatment includes cardiac ablation.

[0040] (Example 6) The method according to any one of Examples 1 to 5, wherein outputting the timing includes outputting the timing to a cardiac ablation algorithm.

[0041] (Example 7) The method according to any one of Examples 1 to 5, wherein outputting the timing includes displaying the timing on a display device (27).

[0042] (Example 8) System (10) includes a circuit (200) and a processor (56). The circuit (200) is configured to measure the 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 from the measured impedance, (ii) associate the temporal minimum value of the total impedance value with the timing of the end of expiration of the patient, and (iii) output the timing of the end of expiration to a user.

[0043] The embodiments described herein primarily address cardiac diagnostic applications, but the methods and systems described herein may also be used for other medical applications.

[0044] It will be understood that the embodiments described above are presented by way of example and that the present disclosure is not limited to what is particularly illustrated and described above in this specification. Rather, the scope of the present disclosure includes both the various combinations and sub - combinations of the functions described above, as well as those variations and modifications thereof that would occur to those skilled in the art upon reading the foregoing description and that are not disclosed in the prior art.

[0045] 〔Embodiments〕 (1) A method comprising: measuring the body impedance as a function of time using a plurality of electrodes attached to a patient; calculating a total impedance value as a function of time from the measured impedance; associating the temporal minimum value of the total impedance value with the timing of the end of expiration of the patient; and outputting the timing of the end of expiration. (2) The method according to embodiment 1, wherein the plurality of electrodes includes electrodes of an electrical position tracking system. (3) The method according to embodiment 1, wherein calculating the total impedance value includes calculating the reciprocal of the trace of a conductivity matrix. (4) The method according to embodiment 1, comprising applying a medical treatment to the patient within a time window around the timing of the end of exhalation. (5) The method according to embodiment 4, wherein the medical treatment includes cardiac ablation.

[0046] (6) The method according to embodiment 1, wherein outputting the timing includes outputting the timing to a cardiac ablation algorithm. (7) The method according to embodiment 1, wherein outputting the timing includes displaying the timing on a display device. (8) A system comprising: a circuit configured to measure the impedance of a body as a function of time using a plurality of electrodes attached to a patient; a processor; wherein the processor is configured to: calculate a total impedance value as a function of time from the measured impedance; associate the temporal minimum value of the total impedance value with the timing of the end of exhalation of the patient; output the timing of the end of exhalation to a user. (9) The system according to embodiment 8, wherein the plurality of electrodes includes electrodes of an electrical position tracking system. (10) The system according to embodiment 8, wherein the processor is configured to calculate the total impedance value by calculating the reciprocal of the trace of a conductivity matrix.

[0047] (11) The system according to embodiment 8, wherein the processor is further configured to apply a medical treatment to the patient within a time window around the timing of the end of exhalation. (12) The system according to embodiment 10, wherein the medical treatment includes cardiac ablation. (13) The system according to embodiment 8, wherein the processor is configured to output the timing by outputting the timing to a cardiac ablation algorithm. The system according to embodiment 8, wherein the processor is configured to output the timing by displaying the timing on a display device.

Claims

1. 1. A system comprising: a circuit configured to measure body impedance as a function of time using a plurality of electrodes attached to a patient; A processor; wherein the processor: calculating a total impedance value as a function of time from the measured impedances; correlating a temporal minimum of the total impedance value with a timing of end-expiration of the patient; and outputting the end-tidal timing to a user.

2. The system of claim 1 , wherein the plurality of electrodes comprises electrodes of an electronic position tracking system.

3. The system of claim 1 , wherein the processor is configured to calculate the total impedance value by calculating an inverse of a trace of a conductivity matrix.

4. The system of claim 1 , wherein the processor is further configured to apply a medical treatment to the patient in a window of time about the timing of end-expiration.

5. The system of claim 3 , wherein the medical procedure comprises cardiac ablation.

6. The system of claim 1 , wherein the processor is configured to output the timing by outputting the timing to a cardiac ablation algorithm.

7. The system of claim 1 , wherein the processor is configured to output the timing by displaying the timing on a display device.

8. 1. A method comprising: measuring body impedance as a function of time using a plurality of electrodes attached to the patient; calculating a total impedance value as a function of time from the measured impedances; correlating a temporal minimum of the total impedance value with a timing of end-expiration of the patient; and outputting the end-tidal timing.

9. The method of claim 8 , wherein the plurality of electrodes comprises electrodes of an electronic position tracking system.

10. The method of claim 8 , wherein calculating the total impedance value comprises calculating an inverse of a trace of a conductivity matrix.

11. 10. The method of claim 8, comprising administering a medical treatment to the patient in a time window around the timing of end-tidal expiration.

12. The method of claim 11 , wherein the medical procedure comprises cardiac ablation.

13. The method of claim 8 , wherein outputting the timing comprises outputting the timing to a cardiac ablation algorithm.

14. The method of claim 8 , wherein outputting the timing comprises displaying the timing on a display device.

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