Surgery – Diagnostic testing – Detecting nuclear – electromagnetic – or ultrasonic radiation
Reexamination Certificate
2002-04-30
2004-01-27
Jaworski, Francis J. (Department: 3737)
Surgery
Diagnostic testing
Detecting nuclear, electromagnetic, or ultrasonic radiation
C600S443000, C600S447000, C600S455000
Reexamination Certificate
active
06682485
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to apparatus and methods for the measurement of physiological functions, and, more particularly, to noninvasive apparatus and methods for the measurement of cardiac valve function.
2. Description of Related Art
Background on Cardiovascular Function Assessment Techniques
The cardiac cycle in a human heart is a well-studied phenomenon. As shown in
FIG. 1
(Guyton, Basic Human Physiology, W.B. Saunders Co., Philadelphia, Pa., 1971), pressure, volumetric, electrical, and audible events can be correlated with the stages of the cardiac cycle.
Electrocardiograms (EKGs) detect the electrical potentials generated in the heart, but their interpretation is largely empirical, as the phenomena the peaks represent are not wholly understood, and diagnoses are primarily made via pattern matching techniques against known normal and disease states. Some myopathies that can be detected with an EKG are ventricular hypertrophy, bundle branch blocks, and fibrillation. However, such problems as valvular stenosis and regurgitation cannot be detected with an EKG, nor can transvalvular pressure gradients be assessed.
Cardiac catheterization is a technique that is used to measure blood pressure in various areas of the heart, as well as blood pumping rate and blood chemistry analysis. This procedure, however, has a nontrivial risk associated with it, even in relatively healthy patients, and infants and heart transplant patients are typically not candidates.
Echocardiographic techniques, including Doppler echocardiography, utilizes returned ultrasound pulses to map a graphic image of the heart and blood vessels, yielding information on the size, shape, and motion of the heart chambers and great vessels and the motion of the heart valves. It has recently been found that this method can compare favorably with cardiac catheterization in making assessments of cardiac hemodynamics in patients with cardiac disease (Dobaghi et al.,
Am. J. Cardiol
. 76, 392, 1995; Nishimura and Tajik,
Prog. Cardiovasc. Dis
. 36, 309, 1994).
Esophageal echocardiography, in which a tube is placed down the patient's throat for visualizing the back of the heart, can detect a valve leakage, but this technique is expensive and uncomfortable, and requires great expertise to administer.
Heart sounds, which have been monitored in a gross manner via auscultation for hundreds of years, are representative of the vibration of the walls of the heart and major vessels around the heart caused by closure of the valves. The phonocardiogram is a recording of amplified low-frequency heart sounds detected by a microphone placed on the patient's chest. Abnormalities such as mitral and aortic stenosis, mitral and aortic regurgitation, and patent ductus arteriosus can be detected with this noninvasive technique.
Valve Area Assessment Techniques
As early as the 1930s methods for obtaining sufficient hemodynamic information for the assessment of valvular stenosis through the application of hydraulic principles were becoming routinely available. However, it was not until 1951 that Gorlin and Gorlin published an orifice formula based upon hydraulic principles using information derived from cardiac catheterization.
The work of Gorlin and Gorlin represented a major advance in the diagnosis of stenotic valvular cardiac disease through the ability to reproducibly quantify the degree of stenosis in terms of valvular area. While this method has become almost universally accepted as the standard for assessing valvular stenosis, it does subject the patient to the highly invasive procedure of cardiac catheterization. It would be rewarding both from the point of view of improved patient care and evaluation and in the further understanding of cardiac mechanics if a method were developed that used diagnostic parameters of a less invasive nature than is the current practice.
The principal hemodynamic manifestations of a significant degree of aortic stenosis include an increased left ventricular pressure, “a” waves in the left atrial pressure pulse, an abnormally large systolic aortic valve pressure gradient whose value depends on the forward systolic flow rate, central aortic pressure pulse abnormalities, a prolonged systolic ejection interval and reduced cardiac output and coronary blood flow.
All these measurable manifestations of aortic stenosis are related to the degree of valvular stenosis but do not, in themselves, provide a quantification of the magnitude of the obstruction. Alterations in the fundamental hemodynamic variables of stroke volume, aortic valve pressure gradient and left ventricular ejection period are the basis for interpreting the principle clinical manifestations of aortic stenosis.
The hemodynamic foundation for the quantification of aortic stenosis from the fundamental variables was established by the investigations of Gorlin and Gorlin (1951). The principal result of these studies was the development of a hydraulic orifice formula that derived from a combination of two basic laws of fluid physics, the conservation of energy and conservation of mass. The resulting orifice formula determined the degree of outflow obstruction as specified by the aortic valve cross-sectional area. The valve area is precisely related to stroke volume, aortic valve pressure gradient, and systolic ejection time. Since the introduction of this hydraulic formula, it has become the most generally accepted diagnostic procedure for the accurate quantification of the degree of obstruction associated with aortic stenosis.
Despite the fundamental character of a diagnosis via the Gorlin formula, the highly invasive nature of the required hemodynamic measurements often necessitates diagnostic procedures of a less precise nature. Thus it would be desirable to provide a technique that would provide more precise data while at the same time presenting no risk to the patient.
Valve Pressure Gradient Assessment Techniques
Mitral valve disease is the result of a reaction on cardiac valve tissue of the body's defense mechanisms against a particular form of streptococcal infection known as rheumatic fever.
As a result of the relatively good public health measures in the industrialized world, mitral valve disease no longer represents the critical proportions that it assumes in the undeveloped world. Nevertheless, this disease still accounts for a significant health care concern. Statistics of the American Heart Association for 1978 indicate that approximately nine million adults have rheumatic heart disease in the United States, and the death rate due to this affliction is about 13,000 per year. Over one-half of all patients with rheumatic heart disease also develop mitral stenosis, and of this number 66% are women.
Of particular concern is heart disease in pregnancy. Heart disease of all classes occurs in approximately 1% of women of child-bearing age; however, rheumatic heart disease, particularly mitral stenosis, accounts for 90-95% of heart disease observed during pregnancy. Perinatal mortality rates are also strongly dependent on the degree of mitral stenosis. The infant mortality rate is approximately 12% for conditions of moderate maternal mitral stenosis and over 50% for severe mitral stenosis.
To minimize the maternal and fetal risks, it is recommended that pregnancies complicated by mitral stenosis be followed by serial observations of functional cardiac status. An important parameter of this abnormality is the capillary wedge pressure; however, it is clearly not feasible to perform serial catheterizations under these conditions.
Patients who have severe mitral valve disease are often given artificial valve replacements. While artificial valves alleviate the problem of stenosis, it is not uncommon for thrombi to form on the mechanical structures, producing systemic emboli and valve obstruction or re-stenosis. For this reason serial observation of the valve for possible malfunction and flow obstruction is important. Increased obstruction of the valve manifests itself by increas
Olsen Steven P.
Seitz Walter S.
Allen Dyer Doppelt Milbrath & Gilchrist, P.A.
Jain Ruby
Jaworski Francis J.
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