Surgery – Diagnostic testing – Cardiovascular
Reexamination Certificate
2000-09-25
2002-06-04
Nasser, Robert L. (Department: 3736)
Surgery
Diagnostic testing
Cardiovascular
Reexamination Certificate
active
06398738
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a method and apparatus for using reduced sized measurement devices with balloon assist catheters. In particular, the invention relates to an improved method and apparatus for controlling the inflation of a balloon assist catheter by using a pressure sensor to determine when to inflate and deflate the balloon to obtain maximum circulation effects.
Moreover, the invention relates to a method and apparatus for measuring mean blood pressure using a cardiac assist balloon catheter. In particular, this aspect of the invention relates to an improved method and apparatus for detecting mean pressure and using that measurement to reconstruct a high fidelity blood pressure waveform.
BACKGROUND OF THE INVENTION
Catheter tip measurement devices are catheters that have measurement sensors located at or near their distal tips. These devices are used in a variety of applications to measure internal properties of internal tissues and fluids such as blood volume, velocity, and pressure. Catheter tip measurement devices may be introduced directly into arteries, veins, or other body organs either by themselves or through other catheters that have been previously positioned within a patient. Catheter tip measurement devices generally have electrical or fiber optic connectors at the proximal end of the catheter that communicate data from the measurement sensors to external processing devices. One type of catheter tip measurement device is a catheter tip pressure transducer, which has at least one pressure transducer located at or near the distal tip of the catheter.
The size of the catheter tip is important, and for many applications, this size is the primary limiting factor that determines whether a measurement catheter may be used in a particular application. For example, size is important and is a limiting factor in measuring pressure within small vessels, such as coronary arteries. Size is also important where a catheter tip measurement device is being introduced through the lumen of another catheter. One such application is where a small sized catheter tip pressure transducer is introduced through the lumen of an electrode or conductance catheter. A conductance catheter has electrodes disposed at the distal end of the catheter to measure the resistivity of the blood, thereby determining the heart chamber volume. These measurements can be translated into volume and impedance measurements of heart segments on a beat-by-beat basis. A catheter tip pressure transducer introduced through the lumen of a conductance catheter allows for simultaneous measurement of pressure at the tip of the conductance catheter. In this way, the conductance catheter can be used for volume measurements, and the catheter tip pressure transducer can be used for pressure measurements. The resulting pressure/volume loops are of significant diagnostic value in many types of heart disease.
Present small-size catheter devices capable of making internal pressure measurements take the form of fluid-filled devices, electrical strain gauge type transducer devices, and fiber optic devices. Fluid-filled devices may have very small construction, but such devices provide poor measurement fidelity. Similarly, fiber optic devices may have a very small sensor size, but such devices have relatively unstable and unacceptable performance. In contrast, strain gauge type transducer devices, which utilize semiconductor pressure transducers, provide high-fidelity measurements but suffer from requiring a significantly larger feature size.
In addition to catheters with pressure transducers and other measurement devices at their distal tip, guidewires exist with measurement devices at their tip. Guidewires may be inserted into body organs and used to guide the insertion of a variety of catheters into the human body. Often catheters are too large and bulky to introduce them directly into arteries, veins, or other body organs. Therefore, smaller, more flexible guidewires are introduced into the body. Then, a catheter is slipped over the guidewire for insertion. The guidewire guides the catheter into the artery, vein, or body organ.
Guidewires may also be used to exchange catheters into arteries, veins, and body organs (referred to as “exchange guidewires”). When a catheter must be removed and replaced, an exchange guidewire is inserted through the lumen of the catheter. The catheter is then removed, leaving the guidewire in place. The replacement catheter may then be inserted by slipping it over the existing guidewire. When a guidewire with measurement devices at the distal tip includes external equipment associated with the measurement device, it is necessary to include a connector between the guidewire and the equipment. This connector allows the external equipment to be removed from the guidewire in order to permit the exchange of catheters.
Some guidewires include measurement devices at the distal tip. However, these guidewires either do not have very small construction because of the use of the pressure sensor at the distal tip, or they lack the measurement accuracy and stability required for most applications. For example, U.S. Pat. No. 4,941,473 illustrates a guidewire with a pressure sensor at the distal end of the guidewire. The guidewire comprises an optical fiber surrounded by a helically wound metal wire. The thickness of the helically wound metal wire and the tightness of the winding determine the torsional stiffness of the guidewire. Although this construction may allow for small feature sizes, it does not provide the measurement accuracy and stability required for most applications. In particular, this guidewire uses optical fibers to connect a pressure sensor to its associated measurement equipment. This device expands and distorts when inserted into the body due to temperature variations, causing a zero level shift in the measured pressure.
Another potential application for pressure measurement devices is with balloon assist catheters. Balloon assist catheters are flexible polyurethane bladders used to assist the heart with circulating blood through the body.
FIG. 1
illustrates a human heart. In operation, a balloon assist catheter would be inserted through the femoral artery, fed through the artery, and placed approximately just below the aortic notch
5
within the aorta
4
. The aorta
4
is the primary artery for delivering blood from the heart
2
to the systemic circulation system. Once in position, the balloon assist catheter is ideally inflated with helium immediately after the aortic valve
6
closes. When the balloon is inflated, the aortic diastolic pressure is increased and blood is pushed through the aorta
4
away from the heart
2
. As the aortic valve opens, the balloon deflates rapidly, producing a decrease in aortic systolic pressure with a consequent decrease in resistance when the left ventricle
8
attempts to pump blood through the systemic circulation system. By inflating and deflating the balloon as described, which is referred to as counterpulsation, circulation of blood through the body may be improved. For a more complete discussion of the operation and use of intraaortic balloons, see
CARDIAC CATHETERIZATION AND ANGIOGRAPHY
, 3rd ed., Lea and Febiger, at pp. 493-501.
The inflation and deflation cycle lasts for approximately 225 milliseconds and timing of the cycle is critical to obtain maximum circulatory effect. If balloon inflation occurs too early, backflow of blood may occur into the heart. Likewise, if balloon inflation occurs too late, maximum circulation effects may not be obtained.
Traditionally, timing of the inflation of the balloon has been done by a human operator based on an electrocardiogram as shown in FIG.
2
. The electrocardiogram (ECG) provides a graphic recording of the electrical manifestations of the heart action as obtained from the body surfaces. The ECG has three predominant wave forms, commonly known as the P wave, representing atrial depolarization; the QRS complex, representing ventricular depolarization, which is coincident w
Millar Instruments, Inc.
Nasser Robert L.
Thompson & Knight LLP
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