Surgery – Diagnostic testing – Cardiovascular
Reexamination Certificate
1999-11-19
2001-08-21
Nasser, Robert L. (Department: 3736)
Surgery
Diagnostic testing
Cardiovascular
C600S505000, C607S018000, C607S023000
Reexamination Certificate
active
06277078
ABSTRACT:
FIELD AND BACKGROUND OF THE INVENTION
The present invention relates to a system and method for monitoring of at least one parameter associated with the performance of a heart. More particularly, the present invention relates to a system of intrabody implantable sensors with which the performance of a heart can be monitored at any given time point along a prolonged time period.
Chronic heart failure (CHF) results from a deterioration in heart function and is characterized by patterns of hemodynamic, renal, neural and hormonal responses.
The physiological disturbances in congestive heart failure are complex, but a common feature is impairment in the performance of the heart as a pump.
Congestive heart failure is typically brought on by left ventricular dysfunction (LVD). LVD is a condition characterized by impairment in the function of the left ventricular muscle. As a result of this impairment, a reduced cardiac output (which is the product of heart rate multiplied by stroke volume), and an increase in filling pressure are experienced. Left ventricular dysfunction is typically brought on by diseases such as ischemic heart disease, hypertensive heart disease, valvular heart disease, cardiomyopathies and myocarditis. Right ventricular dysfunction (RVD), is a condition of the right ventricle of the heart which is similar to LVD. RVD is usually secondary to LVD, but occasionally can result from a pulmonary disease, valvular pulmonic stenosis, or direct damage to the right ventricular myocardium.
A range of compensatory mechanisms are activated in response to congestive heart failure, which mechanisms are aimed at correcting the reduced cardiac output. These include intrinsic cardiac mechanisms such as, muscle stretching (to increase contractile power), hypertrophy (increase in muscle mass), and a change in the shape of the ventricle. Additionally, a neuro-endocrine response is evoked, leading to an adrenergic increase in heart rate and contraction force, activation of the Renin-Angiotensin-Aldosterone-System (RAAS) which induces vasoconstriction, fluid retention, and redistribution of blood flow. While the neuro-endocrine response is compensatory, it tends to overload the cardiovascular system, leading to additional myocardial damage, and eventually congestive heart failure.
The diagnosis of CHF is achieved by a combination of non-invasive and invasive procedures. These procedures include physical examination, electrocardiogram (ECG), blood tests, chest radiography and echocardiography. Additional tests may be prescribed if needed to establish the presence of the disease and it's etiology.
Management of a CHF patient is often an enormous challenge to the treating physician. The compensatory mechanisms evoked by heart failure, make it necessary to provide treatment at a broad front, which typically requires the balancing of several potent drugs. At times this treatment is thwarted by the compensatory mechanisms, which recompensate for the presence of the medical treatment. Thus, the medical treatment of CHF is more of a “disease management” task than a “treatment”, and in essence relies upon balancing the hemodynamic status of the patient in a state of compensation, such that the progression of CHF is kept to a minimum.
The management of CHF also includes non-medical intervention such as exercise to the extent tolerated, weight control, sodium restriction, and abstinence from smoking and alcohol.
The delicate balance between compensation and effective treatment is easily upset, even by seemingly benign factors, such as common medication (e.g., aspirin), physiological factors, excitement, or gradual progression of the disease. This may plunge the patient into a decompensation crisis, which requires immediate corrective action so as to prevent the deterioration of the patient's condition which, if left unchecked, can lead to death.
Central to disease management is constant patient monitoring. Presently, the most commonly used monitoring devices, monitor parameters which indirectly indicate the hemodynamic status of the patient. However, different hemodynamic situations, which require radically different corrective actions, may present similar clinical findings and as such a correct treatment regimen cannot always be prescribed by a physician. Monitoring of more direct hemodynamic measures requires more complex procedures, such as echocardiography or invasive methods. These procedures are usually employed only when a hemodynamic crisis has developed, or when trial and error treatment has failed to produce the desired results. An additional obstacle to proper patient management is the frequency of monitoring. A hemodynamic crisis may develop in a matter of hours or days. Alternatively, the patient may go through a phase where the hemodynamic parameters slowly change into a decompensatory state in which case monitoring over a long period of time is required in order to detect the onset of such a change.
There are various methods to measure heart performance and as such to detect CHF. These methods are categorized as non-invasive or invasive measurement methods.
Non-invasive measurement methods obtain information which relates indirectly to the performance of the cardio-vascular system.
For example, measurements of lung partial oxygen pressure (pO
2
) at exhale can be exercised to monitor the state of a patient. Such measurements are cheap to perform and are non-invasive by nature, but the results are not considered a valid measure of the cardiac status in CHF unless corroborated by another independent measurement. Another method to determine pO
2
relies upon the metabolic rate ratio (see, for example, U.S. Pat. Nos. 4,909,259 and 5,836,300). The concentrations of oxygen and carbon dioxide in the breath of the patient are measured. The data obtained by these measurements also includes the effects of cardiac output (CO), lung problems and various other metabolic parameters and, as such this method requires additional data to be accurate.
Attempts have also been made to derive the principal CO parameters from ECG waveforms using an experimental model which relates stroke volume with ECG electrical parameters (see, for example, U.S. Pat. Nos. 5,025,795 and 4,854,327). Although these methods can easily be applied to long-term disease management, the lack of data pertaining to the significance and validity of the experimental model and its dependence on stress, past cardiac events and other parameters is not provided and as such these methods cannot be considered accurate. Moreover, none of these methods can be used to determine with accuracy the left ventricle filling pressure which is a crucial parameter for proper patient management.
The condition of a CHF patient can also be assessed by the heart size. This can be accomplished non-invasively by either x-rays or by an echo-cardiography, although in both cases highly accurate readings cannot be collected.
U.S. Pat. No. 5,178,151 discloses a non-invasive heart function monitor which measures cardiac volumes from torso movements in two planes combined with ECG measurements. An elaborate model is used to extract these volumes from the data. A highly skilled staff is required to assess the results of this procedure.
U.S. Pat Nos. 5,469,859; 5,735,284 and 4,450,527 all describe a non-invasive bio-impedance devices which employ two to four thoracic or peripheral electrodes utilizable in determining a patient's cardio-respiratory parameters. Although this approach can be used for long term disease management due to its simplicity and non-invasiveness, it suffers from several drawbacks. For example, the results obtained depend on perfect electrical coupling to the body at precise locations. In addition, since the electrical path in the human tissue is complex and varies with the individual and his/her breath regimen, the method yields semi-accurate results which oftentimes have to be correlated to other measurement methods. Finally, due to its non-specificity, the obtained CHF related results may be contributed by other edemic proce
Penner Abraham
Porat Yariv
Rozenman Yoseph
Nasser Robert L.
Remon Medical Technologies Ltd.
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