Surgery – Diagnostic testing – Cardiovascular
Reexamination Certificate
1998-12-03
2001-04-17
O'Connor, Cary (Department: 3736)
Surgery
Diagnostic testing
Cardiovascular
C600S485000, C600S493000, C600S453000, C600S454000, C600S455000
Reexamination Certificate
active
06217522
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method and system for the non-invasive determination of the pressure-volume loop (PVL) of the heart.
BACKGROUND OF THE INVENTION
The heart, as is known, is a pump and, as such, produces pressure that causes the blood to circulate through the system. A widely used graphic representation of the cardiac function is known as the pressure-volume loop (PVL), referring to the relationship, in the left ventricle, between pressure and volume during a single cardiac cycle which consists of four main phases: (1) the heart being filled with blood; (2) the heart generating enough pressure to overcome arterial resistance; (3) the heart ejecting blood into the arteries, and (4) pressure in the heart dropping so that it is ready to receive blood again.
PVLs have a variety of uses. They have been found to reliably depict various external influences on the heart, such as exercise, drug therapy, cardiac disease, etc. PVLs are an irreplaceable research tool in the field of cardiac mechanics, and are extensively used in the teaching of medical students. Other parameters which can be determined with the aid of the method and system according to the present invention include cardiac power, cardiac peak power and contractile reserve.
Cardiac power, the power of the heart muscle, representing the pumping capability of the heart (in units of work/time), is a known index of the heart's pumping ability to increase power has been shown to be directly related to the survival of patients with severe heart failure [Tan, 1987]. Recent studies have shown the cardiac peak power, i.e., the maximum instantaneous cardiac power during blood ejection, to be an accurate descriptor of the heart's contractility, the quality of the heart muscle, representing its ability to contract [Kass and Beyar, 1991].
The present invention measures cardiac power as well as power increase under stress, thus calculating contractile reserve (CR), the difference between cardiac peak power and cardiac power at rest. CR can be used to arrive at a prognosis for heart failure patients, and thus to decide the timing of heart transplantation or other therapy. CR is an excellent tool for following the treatment of heart patients and for diagnosing heart disease.
Despite its many uses, no easy way has so far been found to produce PVLs. The only method of doing so until now has been by means of cardiac catheterization, which is an invasive procedure that, as all invasive procedures, puts the patient at a non-negligible risk, is very costly in that it requires a large, highly trained staff, and consequently is not performed in every hospital.
OBJECT OF THE INVENTION
It is thus one of the objects of the present invention to provide a method for determining a patient's PVL by exclusively non-invasive and therefore non-hazardous means, a method that can be applied by a relatively small team of medical personnel mostly on the technician level, and that is therefore within the means of even small medical facilities.
SUMMARY OF THE INVENTION
According to the present invention, the above object is achieved by providing a method for the non-invasive determination of the pressure-volume loop (PVL) of a patient's heart, comprising the steps of connecting said patient to an electrocardiograph; mounting the probe of an echo-Doppler device on the patient in a position enabling it to sense the aortic root and to produce signals representative of the flow waves issuing from said aortic root; analyzing said signals and obtaining a series of data points as pairs of flow and time, using the QRS complex of the electrocardiogram pattern as a time reference point; applying a curve-fitting procedure to turn said data points into a flow curve resembling the flow wave issuing from said aortic root; placing a pressure cuff on the patient's arm and inflating it to a point where all flow in the patient's brachial artery stops; deflating said cuff throughout deflation; during deflation, sensing blood flow penetrating the barrier constituted by said pressurized cuff, with instantaneous pressure at the aortic root being equal to instantaneous pressure inside said cuff; obtaining a series of data points from peak systolic to diastolic pressure, each point consisting of cuff pressure at penetration coupled with the time of its occurrence after the corresponding QRS complex; applying a curve-fitting procedure to turn said data points into a pressure curve resembling the ascending limb of the aortic pressure wave; calculating the end systolic pressure (ESP) using the expression ESP=DP+⅔ (PSP−DP), where DP=diastolic pressure and PSP=peak systolic pressure; calculating volume at point ESP by integrating said flow curve throughout the ejection phase of the patient's heart, and viewing said PVL on a monitor screen.
The invention further provides a system for the non-invasive determination of the pressure-volume loop (PVL) of a patient's heart, comprising electrocardiograph means having electrodes attachable to selected points on the body of said patient; a pressurizable cuff mountable on an arm of said patient; computer means provided with display means connectable to said electrocardiograph means and to said pressurizable cuff via a pressure card, and monitoring means locatable externally of said patient in such a position as to be capable of monitoring the aortic root of said patient's heart, the output of said means leading at least indirectly to said computer means.
The invention will now be described in connection with certain preferred embodiments with reference to the following illustrative figures so that it may be more fully understood.
With specific reference now to the figures in detail, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of the preferred embodiments of the present invention only, and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the invention. In this regard, no attempt is made to show structural details of the invention in more detail than is necessary for a fundamental understanding of the invention, the description taken with the drawings making apparent to those skilled in the art how the several forms of the invention may be embodied in practice.
REFERENCES:
patent: 5086776 (1992-02-01), Fowler et al.
patent: 5370122 (1994-12-01), Kunig et al.
patent: 5634467 (1997-06-01), Nevo
Dubno Herbert
Natnithithadha Navin
O'Connor Cary
Pyrotec Limited
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