Surgery: light – thermal – and electrical application – Light – thermal – and electrical application – Electrical therapeutic systems
Reexamination Certificate
2000-07-06
2001-11-06
Jastrzab, Jeffrey R. (Department: 3762)
Surgery: light, thermal, and electrical application
Light, thermal, and electrical application
Electrical therapeutic systems
C600S513000, C600S526000, C607S024000
Reexamination Certificate
active
06314323
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a heart stimulator for electrical stimulation of the heart of the type having means for determining cardiac output and control means for controlling the stimulation in response to the determined cardiac output, and wherein cardiac output determining means includes means for measuring the pressure inside the right ventricle and producing a corresponding pressure signal, and means for producing from the pressure signal a control signal related to the cardiac output and supplying the control signal to the control means for controlling the delivered stimulation according to the control signal.
2. Description of the Prior Art
Several other manners of automatic adaption of pacemaker stimulation algorithms and parameters are also known. A common shortcoming to all these prior concepts is that no really appropriate criteria have been found for the algorithm and parameter optimization. Thus attempts have been made to e.g. optimize the AV-delay based on an assumed algorithmic relation between cardiac rate or cardiac activity and an optimal AV-delay. However, the results have been unsatisfactory.
Because of the wide variety of conditions affecting the needs of the patient, such as mental onset, nutrition, time of the day and season, diseases and individual peculiarities, it is not likely that an algorithmic relation will ever come close to the real situation. A system of this kind is unlikely to be effective unless the effectiveness can be measured and used as feedback in a stimulation control. Today pacemaker parameters are normally adjusted depending on diagnosis and the experience of the medical personnel.
The above mentioned U.S. Pat. No. 5,156,147 describes a rate adaptive pacemaker having a variable rate cardiac stimulating pulse generator and a sensor for monitoring some physiologic parameter for adjusting the pulse generator stimulation rate to meet physiologic demands. In addition thereto a hemodynamic sensor is operative to provide an output signal representing the pumping performance of the heart in response to the pacing stimulation. The hemodynamic monitoring sensor may measure the right ventricular pressure, and it is mentioned that the hemodynamic parameter used for controlling the pacing output is determined from the measured pressure signal.
The above subject is achieved in accordance with the principle of the present invention in a heart stimulator having a circuit for determining cardiac output and for producing a control signal corresponding to the cardiac output, a controller for controlling cardiac stimulation dependent on the control signal, and wherein the cardiac output determining circuit includes a pressure sensor which measures pressure in the right ventricle and which generates an electrical signal to corresponding to the measured pressure, an integrator supplied with the pressure signal which integrates the pressure signal between a start time and a stop time to produce an integration result, corresponding to the cardiac output, for use as the control signal, and a bandpass filter connected to the integrator and to the pressure sensor for filtering the pressure signal during a systolic phase to identify opening of a valve at the right ventricle as the aforementioned start time for the integration and to identify a closing of this valve as the aforementioned stop time.
Also U.S. Pat. No. 5,183,051 discloses a method for continuously determining cardiac output from measured arterial blood pressure data. Blood pressure is measured non-invasively or minimally invasively and the stroke volume is determined from the stroke area under the pulse pressure curve between the start of the systolic phase and the dicrotic notch, said stroke area being corrected for any surface portions related to reflected pressure waves.
The methods of determining cardiac output according to the two last mentioned publications are used for diagnostic purposes. Nothing is mentioned about using cardiac output as a parameter for controlling a heart stimulator.
The article K. Rohrbach, Ludwig-Maximilians-Universitat Munchen 1991, “Korrelation zwischen Schlagvolumen und abgeleiteten Druckparametern des rechten Herzens—Eine tierexperimentelle Studie-” discloses different methods of determining the stroke volume from a pressure signal obtained in the right ventricle of a pig. According to one method in this thesis is the pressure signal integrated during systole.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a simple arrangement for determining cardiac output as a measure of the effectiveness of the stimulation administered by a heart stimulator, and to use the determined cardiac output in a feedback procedure for adapting the stimulation as needed.
The above object is achieved in accordance with the principles of the present invention in a heart stimulator having a circuit for determining cardiac output and for producing a control signal corresponding to the cardiac output, a controller for controlling cardiac stimulation dependent on the control signal, and wherein the cardiac output determining circuit includes a pressure sensor which measures pressure in the right ventricle and which generates an electrical signal corresponding to the measured pressure, an integrator supplied with the pressure signal which integrates the pressure signal between a start time and a stop time tp produce an integration result, corresponding to the cardiac output, for use as the control signal, and a bandpass filter connected to the integrator and to the pressure sensor for filtering the pressure signal during a systolic phase to identify opening of a valve at the right ventricle as the aforementioned start time for the integration, and to identify a closing of this valve as the aforementioned stop time.
With the heart stimulator according to the invention it is possible in a simple and reliable way to adjust algorithms and one or more stimulation parameters dynamically in response to environmental and demand changes to maintain an optimum cardiac output. Examples of parameters which can be adjusted in such a feedback procedure are AV-delay, stimulation rate, refractory period, stimulation pulse energy, duration, and amplitude.
In an embodiment of the heart stimulator according to the invention cardiac output determining circuit measures the cardiac output on a beat to beat basis. It is then possible to calculate energy effectiveness per beat and hence energy consumption over time for a certain cardiac output. This is of vital importance in a heart stimulator since it is essential not to stress the heart and not to use more energy than needed in a certain situation.
According to another embodiment of the heart stimulator of the invention a sample and hold circuit is connected to the pressure sensor to hold the measured pressure value at the ventricle outflow valve opening, the integrator being controlled by the sample and hold circuit to continue integration as long as the measured systolic pressure is higher than the held valve opening pressure value. This is a practical way of defining the limits for the integration. The determination of these limits are not too critical, since the integrated area has the character of a relative measure and not an absolute one. Thus in practice a change of an input parameter is performed and the corresponding change of the integrated area, representing cardiac output, is observed, and with the aid of this information the next change of the input parameter in order to reach an optimum cardiac output is determined.
In another embodiment of the heart stimulator of the invention, the integrator is adapted to determine, as a measure of cardiac output, the magnitude of an area in the pressure versus time plane limited by the measured ventricular pressure curve as a function of time from ventricle outflow valve opening to valve closure and a straight line between the measured pressure values at ventricle outflow valve opening and closure. The pressure difference between
Jastrzab Jeffrey R.
Oropeza Frances P.
Pacesetter AB
Schiff & Hardin & Waite
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