WO2012015923A1

WO2012015923A1 - Methods and apparatus for noninvasive assessment of the left atrial and left ventricular diastolic function

Info

Publication number: WO2012015923A1
Application number: PCT/US2011/045536
Authority: WO
Inventors: Markus Meyer; Harold L. Dauerman; Martin M. Lewinter
Original assignee: The University Of Vermont And State Agricultural College
Priority date: 2010-07-27
Filing date: 2011-07-27
Publication date: 2012-02-02

Abstract

An esophageal balloon is inserted into the esophagus at a position proximate to the left atrium and pressurized with a fluid to a pressure greater than an expected atrial pressure. Fluid is permitted to be released from the balloon, and the decaying balloon pressure is measured and recorded as the balloon depressurizes. When the balloon pressure decays to a level at which it is approximately equal to the left atrial pressure, the balloon pressure decay transitions from an exponential decay rate to an approximately linear decay rate. The balloon's mean pressure level at this transition is used to determine the atrial pressure in the left atrium.

Description

METHODS AND APPARATUS FOR NONINVASIVE ASSESSMENT OF THE LEFT

ATRIAL AND LEFT VENTRICULAR DIASTOLIC FUNCTION

FIELD

The present invention relates generally to non-invasive monitoring of left atrial and/or left ventricular diastolic function, and more specifically to methods and apparatus for measuring pressure decay in an esophageal balloon to determine left atrial pressure.

DISCUSSION OF RELATED ART

The assessment of the left ventricular chamber diastolic function is especially helpful when evaluating the presence of heart failure or otherwise investigating cardiac function. When left ventricular chamber filling is impaired, the left atrium pressure is elevated. To measure the atrial pressure as part of the assessment of left ventricular filling, a doctor typically inserts a catheter into an artery or a vein, such as the pulmonary artery. The use of a pulmonary artery catheter in patients suffering from acute myocardial infarction has been associated with serious complications.

The esophagus passes proximate to the left atrium. It is known to place a balloon within the esophagus proximate to the left atrium using an esophageal catheter. Pressure oscillations in the balloon are measured as the balloon is inflated, and the amplitude of these oscillations is analyzed with the goal of determining the atrial pressure.

SUMMARY

The inventors have appreciated that measuring pressure decay in an esophageal balloon positioned proximate to the left atrium can be helpful in determining atrial pressure. According to one embodiment, an esophageal balloon is inserted into the esophagus at a position proximate to the left atrium and pressurized with a fluid to a pressure greater than an expected atrial pressure. Subsequently, fluid is permitted to be released from the balloon, and the balloon pressure is measured and recorded as the balloon depressurizes. When the balloon pressure decays to a level at which it is approximately equal to the left atrial pressure, the balloon pressure decay transitions from an exponential decay rate to an approximately linear decay rate. The balloon's mean pressure level at this transition can be used to determine the atrial pressure in the left atrium. According to one embodiment, a method includes inserting a balloon into an esophagus of a person and positioning the balloon proximate to the left atrium of the person, and pressurizing the balloon with a fluid. The method further comprises permitting the balloon to release the fluid such that a pressure of the balloon decays, and periodically measuring the pressure of the balloon as the balloon releases fluid to produce pressure measurements. The pressure measurements are analyzed to determine a mean pressure value at which the pressure decay changed from an exponential decay rate to an approximately linear decay rate.

According to another embodiment, a method includes an act of receiving pressure data, wherein the pressure data includes periodic balloon pressure measurements of a balloon inserted into an esophagus of a person and positioned proximate to the left atrium of the person, the balloon pressure measurements having been measured as the balloon released fluid over a period of time. The method also includes analyzing the pressure measurements to determine a mean pressure value at which the pressure decay changed from an exponential decay rate to an approximately linear decay rate. A further act includes determining an atrial pressure of the person's left atrium based at least in part on the determined mean balloon pressure.

According to a further embodiment, a system includes an esophageal catheter having a balloon configured to be placed within a person's esophagus proximate to the person's left atrium. The system also includes a pressurizer configured to pressurize the balloon with a fluid, a pressure sensor configured to measure a pressure of the balloon, and a processor configured to record repeated pressure measurements of the balloon pressure as the balloon releases fluid and the balloon pressure decays. The processor is further configured to determine a transition in the balloon pressure decay rate from an exponential decay rate to a linear decay rate, and to determine a mean pressure value of the balloon at the transition in the balloon pressure decay rate.

According to yet another embodiment, a method includes acts of inserting a balloon into an esophagus of a person proximate to the left atrium of the person and pressurizing the balloon with a fluid. The method further includes permitting the balloon to release the fluid such that a pressure of the balloon decays, and repeatedly measuring the pressure of the balloon as the balloon releases fluid to produce pressure measurements. The pressure measurements are used to determine a left atrial pressure of the person. BRIEF DESCRIPTION OF FIGURES

Figure 1 is a flow chart representative of a method for using an esophageal balloon as part of determining atrial pressure;

Figure 2 is a graph showing results from a test of methods disclosed herein;

Figure 3 is a flow chart representative of a method for determining an atrial pressure based on esophageal balloon pressure measurements; and

Figure 4 is a schematic drawing showing one embodiment of an apparatus for performing methods disclosed herein.

DETAILED DESCRIPTION

It should be understood that aspects of the invention are described herein with reference to the figures, which show illustrative embodiments in accordance with aspects of the invention. The illustrative embodiments described herein are not necessarily intended to show all aspects of the invention, but rather are used to describe a few illustrative

embodiments. Thus, aspects of the invention are not intended to be construed narrowly in view of the illustrative embodiments. In addition, it should be understood that aspects of the invention may be used alone or in any suitable combination with other aspects of the invention.

Figure 1 is a flow chart showing a method 100 which incorporates one or more aspects of the invention. Method 100 is directed to measuring esophageal balloon pressure decay as part of determining atrial pressure in a patient's left atrium. Knowledge of the atrial pressure is highly advantageous when assessing left ventricular chamber filling, and left ventricular chamber filling is crucial for understanding certain cardiac functions. For example, the methods and apparatus described herein may be used in an intensive care unit setting and/or during transesophageal heart ultrasound to determine left ventricular chamber filling to aid in the diagnosis of conditions such as cardiac shock, non-cardiac shock, heart failure, pulmonary disease, atrial activity in atrial flutter and atrial fibrillation, mitral regurgitation and mitral stenosis.

A balloon is inserted into a patient's esophagus proximate the left atrium (act 102).

The balloon may be inserted through use of a conventional stomach tube or other suitable delivery device. The balloon may be formed of a section of rubber placed over the distal open end of the stomach tube, though other suitable balloon materials may be used. Fluid is added to the balloon to pressurize the balloon in an act 104. The balloon may be pressurized to a pressure which is greater than the expected atrial pressure. For example, in some embodiments, the balloon may be pressurized to a pressure of 50mm Hg using a suitable fluid. If the individual managing the overall procedure has an expectation that the atrial pressure is significantly less than 50mm Hg, he or she may instruct that the balloon be pressurized to a pressure less than 50mm Hg. Similarly, if the expectation is that the atrial pressure is close to or greater than 50mm Hg, an initial pressurization of greater than 50mm Hg may be used. Water or other suitable liquid may be used in some embodiments, while in other embodiments, a suitable gas such as air may be used.

In some embodiments, the volume of fluid which is added to the balloon does not stretch the balloon material. In this manner, the pressure within the balloon is caused by the expansion of the balloon against tissue that is in contact with the balloon rather than tension in the balloon material itself. However, in some embodiments, the balloon may be pressurized to such an extent that the balloon material is placed under tension.

In an act 106, a depressurization of the balloon is initiated. In some embodiments, the depressurization includes opening a valve to permit the balloon to release the fluid contained in the balloon. The valve may be positioned at an end or other portion of the stomach tube which is external to the patient's body. In embodiments where a liquid (such as water) is the fluid that is used to pressurize the balloon, the stomach tube may remain full of liquid so that there are no gas pockets between the filled balloon and the valve where liquid is released from the pressurized portion of the system. The released fluid may be recirculated within the pressurization system in some embodiments, as described in more detail further below with reference to Figure 4.

As the pressure in the balloon decays, periodic measurements are taken in an act 108. The pressure may be measured with a sufficiently high frequency that oscillations in the pressure are measureable. In some embodiments, pressure is measured and recorded once per millisecond.

Analysis of the pressure measurements is performed in an act 110. According to one embodiment, a transition point or region is determined where the decay rate changes from an exponential decay rate to an approximately linear decay rate. For example, referring to Figure 2, a pressure measurement curve 202 shows measured esophageal balloon pressure measurements from a test conducted on a pig. From the start of depressurization at zero seconds until approximately 15 seconds after the start depressurization, the pressure decays at an exponential rate. At approximately 15 seconds, the decay rate transitions to an

approximately linear decay rate. A line 204 that is fit to the linear decay section is shown in Figure 2.

At the transition point of 15 seconds, the mean pressure value of the balloon is approximately Ylmm Hg, indicating that the atrial pressure in the left atrium is approximately Ylmm Hg. A curve 206 representing direct measurements of atrial pressures in the left atrium using a direct pressure line inserted in the left atrium indicates that indeed the mean atrial pressure is approximately Ylmm Hg.

To determine the approximate time of transition of the decay rate from an exponential decay rate to an approximately linear decay rate, curve-fitting software may be used. In some embodiments, a transition may be determined by viewing a display of the pressure measurements and estimating a transition region or point. Similarly, a mean pressure value at the transition may be determined through the use of software or other computation methods, or a mean pressure value may be estimated by viewing a display of the pressure

measurements.

Referring now to Figure 3, a method 300 of determining an atrial pressure in the left atrium is represented with a flow chart. Pressure decay data from an esophageal balloon administration is received in act 302. In some embodiments, the data may be received in an electronic format and may be stored on a computer-readable storage medium. In other embodiments, the pressure decay data may be received in the form of a visual display, such as a computer monitor display or a printed display. The visual display may include a plot of decaying pressure readings over a time period similar to curve 202 shown in Figure 2.

The pressure decay data is analyzed in act 304 to determine a transition of the decay rate. As described above, when the decaying balloon pressure reaches the pressure of the left atrium, the decay rate transitions. According to some embodiments, the transition is from an exponential decay rate to an approximately linear decay rate. In the case of data having been received in an electronic format, the pressure data may be analyzed by a software program or with the help of a software program to determine a point in time or a range of time where such a transition occurred. In some embodiments, the analysis may be performed by a trained professional examining a visual display of the pressure data. The transition may be determined by fitting a line (e.g., line 204 of Figure 2) to a final portion of the pressure readings, extending the line from right to left, and noting when the line separates from the pressure readings curve.

While in some embodiments the analysis of the pressure data occurs after a complete set of pressure data has been collected, in other embodiments analysis may occur while pressure data is continues to be measured. For example, a software program or an observer may monitor the pressure data in real-time or with a slight delay as the data is collected. When the decay rate transitions to an approximately linear decay rate, an indication may be made, and the time may be noted.

The result of the determination of the transition of the pressure decay rate may be a single value or a range of values. For example, the analysis of act 304 may result in a determined transition of a particular time, for example 14.5 seconds after starting

depressurization. In another embodiment, a range may be provided. For example, a transition region of between 14.0 and 15.5 seconds may be output from act 304 in some embodiments.

In an act 306, a mean pressure value at or near the transition time is determined. The mean pressure value may be calculated by averaging all of the pressure readings from one complete cardiac cycle surrounding the transition point. Alternatively, a representative sample of pressure readings from one complete cardiac cycle may be averaged. Other suitable methods of calculating the mean pressure value at or near the transition time may be used.

The atrial pressure of the left atrium is determined based at least in part on the determined mean pressure value of the balloon at the transition. In some embodiments, the atrial pressure is determined to be equal to the determined balloon mean pressure value at the transition. In other embodiments, one or more adjustments may be made to the determined balloon mean pressure value at the transition to arrive at an atrial pressure determination.

One embodiment of a system 400 configured to perform various methods described herein is shown in Figure 4. A controller 402 may be used to control a motor 404 to add fluid to a balloon 406. Motor 404 may push a piston 406 in a cylinder 408 to deliver a fluid, such as water 407, through a tube 410 to balloon 406. Controller 402 may be contained within a PC that is configured to communicate with motor 404, or controller 402 may be physically integrated with fluid delivery apparatus. In alternative embodiments, a pump or other apparatus may be manually activated or actuated to deliver fluid to balloon 406. One or more valves may be included in the fluid delivery and release system, and the valves may be controllable with controller 402, or the valves may be manually openable and closeable. In the illustrated embodiment, a first three-way valve 412 and a second three-way release valve 414 are included so that at least three modes are available: (1) a pressurizing mode during which fluid can be delivered from cylinder 408 to balloon 406, (2) a

measurement mode during which fluid is permitted to be released from the balloon and captured by a reservoir 416, and (3) a recirculation mode during which the fluid can be drawn from reservoir 416 back into cylinder 408 through a tubing 420.

A pressure sensor 422 repeatedly measures the balloon pressure and sends the measurements to a data processor 424. Data processor 424 may be implemented on a PC, within controller 402, or within a processor that is remote from the apparatus.

Of course the embodiment illustrated in Figure 4 is but one example of a system for performing methods described herein, and other system arrangements may be used to practice the methods disclosed herein.

Various sensors may be added to the balloon and/or catheter in some embodiments to provide further functionality. For example, an electrode for sensing atrial electrical activity may be included. A system for use as an atrial pacemaker, and/or a system for lower energy cardioversion of atrial fibrillation and flutter may be included. In still other embodiments, an oxygen sensor for determining oxygen saturation in the left atrium may be included. A system or method for providing an ECG triggered left atrial kick may be included. A system may be included on the catheter for stimulation and/or inhibition of the cardiac sympathetic nervous system. The apparatus may include a needle for penetrating the esophagus and entering the left atrium. A system and method for atrial and mitral valve microinvasive surgery also may be included in some embodiments.

The above-described aspects regarding data recordation, curve-fitting, data processing and/or data analysis can be implemented in any of numerous ways. For example, the embodiments may be implemented using hardware, software or a combination thereof. When implemented in software, the software code can be executed on any suitable processor or collection of processors, whether provided in a single computer or distributed among multiple computers.

Further, it should be appreciated that a computer may be embodied in any of a number of forms, such as a rack-mounted computer, a desktop computer, a laptop computer, or a tablet computer. Additionally, a computer may be embedded in a device with suitable processing capabilities, including a Personal Digital Assistant (PDA), a smart phone or any other suitable portable or fixed electronic device.

Also, a computer may have one or more input and output devices. These devices can be used, among other things, to present a user interface. Examples of output devices that can be used to provide a user interface include printers or display screens for visual presentation of output and speakers or other sound generating devices for audible presentation of output. Examples of input devices that can be used for a user interface include keyboards, and pointing devices, such as mice, touch pads, and digitizing tablets. As another example, a computer may receive input information through speech recognition or in other audible format.

Such computers may be interconnected by one or more networks in any suitable form, including as a local area network or a wide area network, such as an enterprise network or the Internet. Such networks may be based on any suitable technology and may operate according to any suitable protocol and may include wireless networks, wired networks or fiber optic networks.

Also, the various methods or processes outlined herein may be coded as software that is executable on one or more processors that employ any one or more of a variety of operating systems or platforms. Additionally, such software may be written using any of a number of suitable programming languages and/or programming or scripting tools, and also may be compiled as executable machine language code or intermediate code that is executed on a framework or virtual machine.

In this respect, embodiments of the invention may be embodied as a computer- readable storage medium or multiple computer-readable media encoded with one or more programs that, when executed on one or more computers or other processors, perform methods that implement the various embodiments of the invention discussed above.

Computer readable media may include, for example, a computer memory, one or more floppy discs, compact discs (CD), optical discs, digital video disks (DVD), magnetic tapes, flash memories, circuit configurations in Field Programmable Gate Arrays or other semiconductor devices, or other tangible computer storage medium. As is apparent from the foregoing examples, a computer readable storage medium may retain information for a sufficient time to provide computer-executable instructions in a non-transitory form. Such a computer readable storage medium or media can be transportable, such that the program or programs stored thereon can be loaded onto one or more different computers or other processors to implement various aspects of the present invention as discussed above. As used herein, the term "computer-readable storage medium" encompasses only a computer-readable medium that can be considered to be a manufacture (i.e., article of manufacture) or a machine.

Alternatively or additionally, the embodiments of the invention may be embodied as a computer-readable medium other than a computer-readable storage medium, such as a propagating signal.

The terms "program" or "software" are used herein in a generic sense to refer to any type of computer code or set of computer-executable instructions that can be employed to program a computer or other processor to implement various aspects of the present invention as discussed above. Additionally, it should be appreciated that according to one aspect of this embodiment, one or more computer programs that when executed perform methods of embodiments of the present invention need not reside on a single computer or processor, but may be distributed in a modular fashion amongst a number of different computers or processors to implement various aspects of embodiments of the present invention.

Computer-executable instructions may be in many forms, such as program modules, executed by one or more computers or other devices. Generally, program modules include routines, programs, objects, components, data structures, etc. that perform particular tasks or implement particular abstract data types. Typically the functionality of the program modules may be combined or distributed as desired in various embodiments.

It should also be understood that, unless clearly indicated to the contrary, in any methods claimed herein that include more than one step or act, the order of the steps or acts of the method is not necessarily limited to the order in which the steps or acts of the method are recited.

Having thus described several aspects of at least one embodiment of this invention, it is to be appreciated various alterations, modifications, and improvements will readily occur to those skilled in the art. Such alterations, modifications, and improvements are intended to be part of this disclosure, and are intended to be within the spirit and scope of the invention. Accordingly, the foregoing description and drawings are by way of example only. What is claimed is:

Claims

1. A method comprising:

inserting a balloon into an esophagus of a person and positioning the balloon

proximate to the left atrium of the person;

pressurizing the balloon with a fluid;

permitting the balloon to release the fluid such that a pressure of the balloon decays; periodically measuring the pressure of the balloon as the balloon releases fluid to produce pressure measurements;

analyzing the pressure measurements to determine a mean pressure value at an approximate time at which the pressure decay changed from an exponential decay rate to an approximately linear decay rate.

2. The method as in claim 1, further comprising determining an atrial pressure of the person's left atrium based at least in part on the determined mean pressure value.

3. The method as in claim 2, wherein determining the atrial pressure comprises assigning the determined mean pressure value as the atrial pressure.

4. The method as in claim 1, wherein pressurizing the balloon with a fluid comprises pressurizing the balloon with a liquid.

5. The method as in claim 4, wherein pressurizing the balloon with a liquid comprises adding a volume of the liquid to the balloon such that the balloon material is not substantially tensioned.

6. The method as in claim 4, wherein pressurizing the balloon with a liquid comprises pressurizing the balloon with water.

7. The method as in claim 1, wherein the balloon is formed with rubber.

8. The method as in claim 1, wherein the balloon is inserted in the esophagus with a stomach tube.

9. The method as in claim 1, wherein analyzing the pressure measurements comprises using a software program to determine a mean pressure value at an approximate time at which the pressure decay changed from an exponential decay rate to an approximately linear decay rate.

10. the method as in claim 1, wherein pressurizing the balloon comprises pressurizing the balloon to a pressure of at least 50mm Hg.

11. A method comprising:

receiving pressure data, wherein the pressure data includes periodic balloon pressure measurements of a balloon inserted into an esophagus of a person and positioned proximate to the left atrium of the person, the balloon pressure measurements having been measured as the balloon released fluid over a period of time; analyzing the pressure measurements to determine a mean pressure value at an approximate time at which the pressure decay changed from an exponential decay rate to an approximately linear decay rate; and

determining an atrial pressure of the person's left atrium based at least in part on the determined mean balloon pressure.

12. The method as in claim 11, wherein analyzing the pressure measurements to determine a mean pressure value comprises analyzing the pressure measurements to determine an approximate time at which the pressure decay changed and calculating a mean pressure value associated with the time.

13. The method as in claim 11, wherein analyzing the pressure data to determine a mean pressure value comprises using a software program to analyze the data.

14. The method as in claim 13, wherein analyzing the pressure data comprises using a curve fitting program as part of determining the approximate time at which the pressure decay changed from an exponential decay rate to a linear decay rate.

15. The method as in claim 11, wherein analyzing the pressure data to determine a mean pressure value comprises reviewing a visual display of the pressure measurements and determining when the approximately linear decay rate begins.

16. A system comprising:

an esophageal catheter including a balloon configured to be placed within a person's esophagus proximate to the person's left atrium;

a pressurizer configured to pressurize the balloon with a fluid;

a pressure sensor configured to measure a pressure of the balloon; and

a processor configured to

record repeated pressure measurements of the balloon pressure as the balloon releases fluid and the balloon pressure decays;

determine a transition in the balloon pressure decay rate from an exponential decay rate to a linear decay rate; and

determine a mean pressure value of the balloon at the transition in the balloon pressure decay rate.

17. A system as in claim 16, wherein the processor is further configured to determine a mean atrial pressure value based at least in part on the determined mean pressure value at the transition.

18. A method comprising:

inserting a balloon into an esophagus of a person proximate to the left atrium of the person;

pressurizing the balloon with a fluid;

permitting the balloon to release the fluid such that a pressure of the balloon decays; repeatedly measuring the pressure of the balloon as the balloon releases fluid to produce pressure measurements;

using the pressure measurements to determine a left atrial pressure of the person.

19. The method as in claim 18, wherein pressurizing the balloon comprises pressurizing the balloon to a pressure greater than an expected left atrial pressure.

20. The method as in claim 18, wherein pressurizing the balloon comprises pressurizing the balloon to a pressure of at least 50mm Hg.