Surgery – Diagnostic testing – Cardiovascular
Reexamination Certificate
2001-10-11
2003-06-24
Nasser, Robert L. (Department: 3736)
Surgery
Diagnostic testing
Cardiovascular
C600S300000, C600S481000, C435S284100
Reexamination Certificate
active
06582375
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to studying the natural heart in operation and, more specifically, to a system for doing so with the heart explanted outside of the body.
BACKGROUND OF THE INVENTION
The natural human heart and accompanying circulatory system are critical components of the human body and systematically provide the needed nutrients and oxygen for the body. As such, the proper operation of the circulatory system, and particularly, the proper operation of the heart, are critical in the overall health and well-being of a person. A physical ailment or condition which compromises the normal and healthy operation of the heart can therefore be particularly critical and may result in a condition which must be medically remedied.
Specifically, the natural heart, or rather the cardiac tissue of the heart, can fail for various reasons to a point where the heart can no longer provide sufficient circulation of blood for the body so that life can be maintained. To address the problem of a failing natural heart, solutions are offered to provide ways in which circulation of blood might be maintained and improved.
Some solutions involve replacing the heart. Other solutions are directed to maintaining operation of the existing heart. One such replacement solution has been to replace the existing natural heart in a patient with an artificial heart or a ventricular assist device. However, such devices have drawbacks which limit their use to applications having too brief of a time period to provide a real lasting benefit to the patient.
An alternative procedure also involves replacement of the heart and includes a transplant of a heart from another human or animal into the patient. Such a technique also has certain drawbacks. For example, the number of potential donor hearts is far less than the number of patients in need of a natural heart transplant. In addition to requiring removal of an existing organ (i.e. the natural heart) from the patient for substitution with another organ (i.e. another natural heart) from another human, the substitute organ must be “matched” to the recipient, which is difficult, time consuming, and expensive. Furthermore, a risk continues to exist that the recipient's body will still reject the transplanted organ and attack it as a foreign object.
Other attempts to assist the heart, such as wrapping skeletal muscle tissue around the natural heart for contraction, or using an external bypass system, such as a cardiopulmonary (heart-lung) machine, are also accompanied by certain problems or drawbacks. Enveloping a substantial portion of the natural heart with a pumping device for rhythmic compression has also been an attempt to address heart failure. Such attempts and other solutions are set forth in greater detail in U.S. patent application Ser. No. 09/850,554, filed May 7, 2001, entitled “Heart Wall Actuation Device for the Natural Heart,” which is incorporated herein by reference in its entirety.
Another solution, mechanical ventricular wall actuation, has shown promise. As such, devices have been invented for mechanically assisting the pumping function of the heart, and specifically for externally actuating a heart wall, such as a ventricular wall, to assist in such pumping functions.
Specifically, U.S. Pat. No. 5,957,977, issued Sep. 28, 1999, entitled “Activation Device for the Natural Heart Including Internal and External Support Structures,” which is incorporated herein by reference in its entirety, discloses an actuation device for the natural heart utilizing internal and external support structures. U.S. patent application Ser. No. 09/850,554, also discloses actuation devices.
For determining the long-term efficacy of such actuation systems, their operation around and on the heart must be determined. While testing on live animals, and possibly humans, might be desirable, testing on hearts studied out of the body, or ex vivo, is often more practical and desirable. It has been known since the late 19th century that a heart may be isolated ex vivo as a model for the study of myocardial function. This was initially done with animal hearts, requiring the use of animal-derived data to extrapolate to the human condition. Later, human hearts were obtained from cardiac transplant recipients and were restored to a beating condition by being placed on a cardio-pulmonary bypass circuit immediately after explantation from the body.
However, existing heart explantation systems have had some limitations and have precluded the study of global functions, including valvular apparatus, as well as the myocardium. For example, one such explanted heart system operates utilizing models which work via balloons placed in one or both of the ventricles. Such balloons totally bypass the valves and rigidly fix the base of the ventricle. In such a system, the volume assessment of the ventricles has been based either on balloon volume or on assumptions, such as conductance or impedance measurements.
Some systems use crystal-based sonomicrometry techniques which are invalid if ventricular shape changes during an intervention. Also, such systems use large numbers of sonocrystals which make the system expensive. Still further, it is time consuming to precisely position and place the large number of sonocrystals.
An additional problem with existing explanted heart systems is that the hearts are generally suspended by their base, which creates an intracavitary gravitational pressure gradient (from base to apex) that, in diastole, approaches or exceeds the physiologic pressure range for the heart.
Accordingly, it is desirable to provide a system for testing an explanted heart which addresses shortcomings of existing systems, and provides useful data regarding the effect of external conditions on the human heart.
More specifically, it is desirable to have a system which is adaptable to either animal hearts or to human hearts removed for transplant, and which allows previously difficult or impossible ex vivo assessments of devices utilized in the treatment of heart failure. Specifically, it is another objective of the invention to provide such an ex vivo system for testing devices which, either statically or dynamically, change or assist the ventricular operation of the heart to address the effects of heart failure.
It is still another objective of the invention to provide such an assessment system for determining the effect of other factors, such as pharmacological compositions, on the human heart within an ex vivo system.
These objectives and other objectives will become more readily apparent from the further description of the invention set forth below.
SUMMARY OF THE INVENTION
The present invention provides a system and method for studying a beating explanted heart. To invention is utilized to study the characteristics of the heart, and to provide ex vivo assessments of external devices and pharmacological compositions on the heart, such as in the treatment of heart failure or heart disease. The present invention provides a system which creates accurate pressure-volume curves and reduces gravitational effects on the explanted heart. The system maintains valvular function in a nearnormal state while the heart is being studied to determine the effect of interventions on the operation of the valves. The system further provides a high-fidelity, high-frequency ventricular volume determination without requiring the expense and placement of a large number of individual sensors.
In one embodiment, a fluid inflow circuit, including an inflow chamber and a compliance chamber, is coupled to an explanted heart to direct fluid for flowing into a ventricle of the heart, such as through the atrium, or directly into the ventricle through a ventricular inflow valve. The fluid outflow circuit is configured to direct fluid flowing out of the ventricle of the beating heart. Respective flowmeters are coupled with the inflow circuit and the outflow circuit for measuring the inflow rate of fluid directed into the heart ventricle, and out of the heart ventricle. A pressure sens
Klosterman Brad A.
Melvin Alan J.
Melvin David Boyd
Mallari Patricia
Nasser Robert L.
University of Cincinnati
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