Surgery: light – thermal – and electrical application – Light – thermal – and electrical application – Electrical therapeutic systems
Reexamination Certificate
1998-03-02
2001-11-06
Layno, Carl (Department: 3762)
Surgery: light, thermal, and electrical application
Light, thermal, and electrical application
Electrical therapeutic systems
C607S009000, C607S024000
Reexamination Certificate
active
06314322
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to controlling congestive heart failure and, more particularly, to electrically controlling a dilated condition resulting from congestive heart failure.
2. Related Art
The heart pumps blood through a patient's body in order to carry oxygen to, and remove carbon dioxide from, cells located throughout the body. In a patient having a normal heart, the rate at which the blood is pumped through the body increases or decreases to accommodate changes in the physiological needs of the patient. That is, as the cells of the patient's body require more oxygen, the heart rate and/or stroke volume increases to pump more oxygen-rich blood to the cells. When insufficient oxygen is available from the lungs, the respiration rate may also increase to increase the rate of oxygen intake into the body. Conversely, as the demand for oxygen decreases, the heart rate decreases, providing less blood flow and, hence, less oxygen, to the cells.
During a heart cycle, deoxygenated, venous blood enters the right atrium of the heart via the inferior vena cava and the superior vena cava and, during diastole, flows to the right ventricle. The pulmonary artery then delivers blood ejected from the right ventricle into the lungs. The pulmonary vein carries oxygenated blood from the lungs to the left atrium of the heart. During diastole, oxygenated blood flows from the left atrium to the left ventricle, which is filled to its end diastolic volume (EDV). During systole the left ventricle ejects oxygenated blood into the aorta.
The ventricles are cone-shaped muscular chambers that continuously change their shape during the heart cycle. The proper functioning of each ventricle is critically related to its internal dimension, wall thickness and the electrical states of the myocytes. In a normal heart, the left ventricle empties between 56% and 78% of its volume in systole; that is, the stroke volume is between 56% and 78% EDV.
Congestive heart failure (CHF) is a condition in which the heart is unable to provide the necessary amount of oxygenated blood to the body. CHF may be caused by any number of conditions, including high blood pressure, heart valve defects, congenital heart defects, myocardial infarction, irregular heart beat or pulmonary disease. Generally, CHF leads to a progressive dilatation of the heart. This dilatation is typically preceded by compensatory hypertrophy of the heart, or a thickening of the walls of the heart in response to vascular, valvular, or other heart disease. Progressive dilation of the heart increases the risk of developing dilated cardiomyopathy, which is a condition where the ventricles of the heart are weakened to the extent that they contract with less-than-optimal force during systole. This reduction in the systolic function can cause diminished stroke volume and reduced cardiac output.
The more dilated the heart becomes, the less it is able to contract and pump blood from the left ventricle into the aorta. The blood remaining in the heart increases the end-diastolic pressure in the left or right ventricle and, over time, increases the end diastolic volume. The elevated diastolic pressure is also transmitted through the pulmonary vein or artery to the lungs increasing pulmonary capillary pressure. An increase in pulmonary capillary pressure, in turn, can lead to the filling of the lungs with fluid, known as pulmonary edema. With pulmonary edema, breathing becomes more difficult, resulting in dyspnea, orthopnea and/or tachypnea. Furthermore, elevated right ventricular diastolic pressure increases the systemic venous pressure, which leads to peripheral venous congestion and edema.
Another symptom of dilated cardiac myopathy is inadequate blood flow to vital organs due to decreased cardiac output. Resulting problems may include decreased cerebral blood flow, impairing central nervous system function; and reduced blood profusion of the liver and kidneys, impairing hebetic and renal function. If left untreated, the heart's function progressively deteriorates, ultimately resulting in death.
Current treatment of dilated cardiomyopathy generally includes drug treatment. Common treatments include the use of diuretics, digitalis and angiotensin-converting enzyme inhibitors and anticoagulants. However, drug treatment typically does not return the heart to its normal physiological state.
What is needed, therefore, is a system and method that controls the dilatative effects of congestive heart failure, returning the heart to a more normal physiological state without compromising cardiac output or increasing the metabolic needs of the heart. That is, what is needed is a technique that prevents dilation of the heart which leads to the heart's reduced work capacity.
SUMMARY OF THE INVENTION
In one aspect of the present invention, a system for controlling end diastolic volume (EDV) of the heart is disclosed. The system includes an EDV sensor constructed and arranged to measure a parameter related to the end diastolic volume of the heart, and a heart stimulator, responsive to the EDV sensor, constructed and arranged to invoke systole when the measured parameter reaches a predetermined level, the parameter reaching that level prior to termination of diastole. Preferably, the heart stimulator may be a pacemaker. The EDV sensor may be any sensor constructed to measure a parameter related to the end diastolic volume of the heart, or another selected physiological or patho-physiological condition of the heart related to the onset of a compromise in this contractible function of the heart.
In one embodiment of this aspect of the invention, the EDV sensor is a stress/strain sensor. In this embodiment, the strain sensor includes an expandable element implanted on a wall of the heart. Preferably, the expandable element at least partially encircles the heart.
In another embodiment of this aspect of the invention, the EDV sensor is a dimensional sensor. This sensor includes a transmitter constructed and arranged to emit sound waves into the heart; and a receiver constructed and arranged to detect sound waves reflected from various surfaces of the heart. Preferably, the transmitter and receiver include at least one piezoelectric crystal. In one embodiment, the dimensional sensor further includes a coupling medium attached to the piezoelectric crystal, wherein the coupling medium is implantably attachable to a wall of the heart. In one embodiment, the receiver is constructed and arranged to detect multiple sound waves reflected from tissue interfaces in the heart. In a preferred embodiment, the dimensional sensor is further constructed to measure dimensional changes within the myocardium of the heart to afford a measure of stress in the heart wall in accordance with the following equation:
σ
=
Pr
τ
where &sgr; is the stress, P is ventricular pressure, r is the measured ventricular radius and &tgr; is the measured ventricular wall thickness. The stress sensor is further constructed to calculate the ventricular thickness (&tgr;) as a product of a time interval between a first reflected signal and a second reflected signal, and the speed of sound within the heart wall. The stress sensor is further constructed to calculate the ventricular radius (r) by employing the following equation:
r
=
T
E
-
T
D
4
C
B
where T
E
is detected time of a third reflected signal, T
D
is detected time of a second reflected signal, and C
B
is speed of sound in blood.
In another embodiment of this aspect of the invention, the EDV sensor is solely a dimensional sensor. In one embodiment, the dimension sensor includes a band that at least partially encircles the heart to monitor a circumference of the heart. In another embodiment, the dimension sensor includes a band that at least partially encircles the heart, the band including a selected fixed circumference.
In still other embodiments, of this aspect of the invention, the EDV sensor is an impedance sensor, an optical sensor, a microwave sensor, or anoth
Abiomed, Inc.
Cahill Ronald E.
Engellenner Thomas J.
Layno Carl
Nutter & McClennen & Fish LLP
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