Surgery: light – thermal – and electrical application – Light – thermal – and electrical application – Electrical therapeutic systems
Reexamination Certificate
1997-03-04
2001-07-17
Kamm, William E. (Department: 3737)
Surgery: light, thermal, and electrical application
Light, thermal, and electrical application
Electrical therapeutic systems
C607S018000
Reexamination Certificate
active
06263243
ABSTRACT:
Pacemakers that adjust the adaptive heart rate as a function of exertion on the part of the person with the pacemaker are known.
German Patent DE C 34 19 439 describes a pacemaker that with a temperature probe measures the blood temperature of the venous blood in the heart and adjusts the adaptive heart rate as a function of the measured value. This principle is based on the finding that the blood temperature of the human being rises upon exertion. The association of the blood temperature with the physiologically appropriate adaptive heart rate is effected by means of the characteristic curve that allocates one value of the adaptive heart rate to each value of the blood temperature.
A disadvantage of this known pacemaker is that the relationship between the blood temperature and the physiologically appropriate heart rate is as a rule different for each purpose, so that the pacemaker must be calibrated individually for each person with the pacemaker.
Moreover, an exertion-dependent change in the blood temperature—for instance from aging of the temperature probe or if the temperature probe shifts in the body of the person with the pacemaker—also causes a change in the adaptive heart rate, which is physiologically inappropriate.
Many arrangements for measuring impedance in the area of the thorax or in the heart to obtain an impedance signal for rate-adaptive pacemakers are known, and thus the technique of intracardial impedance measurement is familiar per se to one skilled in the art. However, the goal of most of these arrangements is a finding on the tidal volume or cardiac output, as an expression of the physical exertion of the patient and as the actual rate control parameter.
The so-called ResQ method (for Regional Effective Slope Quality) is also known (Max Schaldach, Electrotherapy of the Heart, First Edition, Springer-Verlag, page 114 ff.), in which the course of intracardial impedance over time is utilized to determine the physiologically appropriate adaptive heart rate.
This process is based on the finding that the intracardial impedance, in a particular time window after a QRS complex—the so-called “region of interest” (ROI)—has an especially significant dependency on the exertion of the organism.
The slope of the impedance curve in the ROI is therefore determined, and the difference between the slope of a resting or reference curve and the slope of the currently measured impedance curve (exertion curve) is calculated. Depending on this difference, the adaptive heart rate is set. The association of the calculated slope difference with the heart rate to be set is effected here as well by means of a characteristic curve. Since this relationship is different as a rule for different people, the pacemaker must be calibrated individually for each person, and the calibrations must be repeated if the state of health and exertion capacity change or if the living conditions of the patient change, and then the position of the ROI must also be checked.
SUMMARY OF THE INVENTION
It is therefore an object of the invention in particular to create a pacemaker of the generic type in question that can make do without a patient-specific calibration operation and that adapts automatically to altered peripheral conditions.
The invention encompasses the concept of utilizing the course over time—which because of the linkages via the autonomic nervous system (ANS) is an excellent reflection of the overall exertion situation (physical exercise and psychic stress) of a patent—of the intracardial (and in particular right-ventricle) impedance in a conclusive variable that does not require individual-patient adjustment for the purposes of rate adaptation.
The pacemaker according to the invention evaluates the intracardial impedance, in particular the right-ventricle impedance measured in a unipolar fashion over a wide range, which includes the ROI regions typically established for individual patients. In this region it determines a relationship between a resting or reference curve and an exertion curve, especially by way of an arithmetic processing of the time integral of the impedance over the aforementioned range.
To that end, the output of the integrator stage is connected in particular to an integral value memory, in which one reference integral value at a time, ascertained in at least one preceding cardiac cycle, is stored in memory; and the rate determining device has an arithmetic unit, connected to the output of the integrator stage and the integral value memory, for calculating a secondary impedance variable from the respective primary impedance variable and from the reference integral value in accordance with a predetermined arithmetical equation. In an advantageously simple version, the arithmetic unit has a subtraction stage for forming the differential value between the primary impedance variable and the reference integral value—but some other arithmetic processing may also be done, or optionally a multistage threshold value discrimination as well.
Defining the time range or integration limits requires no patient-individual programming after implantation; instead, these limits can be stored, particularly upon manufacture of the pacemaker, in a read-only memory (ROM) connected (at least indirectly) to one control input of the integrator stage. The limits of the predetermined portion are ascertained as the result of the investigations of the range, relevant to the rate adaptation, of the course over time of the impedance in a patient population.
The aforementioned resting or reference curve is preferably “carried over”, that is, averaged from impedance values obtained over a predetermined period of time of several (for instance, three) minutes; either a sliding averaging or averaging for successive separate periods of time may be done. As a result, rapid adaptation to changing peripheral conditions—such as stimulation parameters, medication or living habits—is attained, and the threat to the patient that would be caused if the pacemaker became stuck at physiologically excessively high rates is avoided.
Upon a transition from spontaneous to stimulated heart activity (upon an increase in exertion) or vice versa, the current impedance curve at the time is expediently defined as the new reference curve. To avoid sudden changes in rate, however, the rate should not be changed at that moment, or should be changed only insignificantly, which requires the introduction of a rate offset amount, which is then gradually reduced again over a predetermined time or a predetermined number of cardiac cycles. Realizing these functions is achieved—along with a suitable embodiment of the pacemaker or sequence controller—by a control connection with the output stage and by an offset memory.
Expanded functionality is offered by equipping the pacemaker with a sensor for an activity variable connected at least indirectly to a control input of the integrator stage and/or a control input of the rate determining device, the output signal of which sensor sets at least one of the limits of the integration range and/or a characteristic curve member of the rate determining device. As an especially simple and also expedient sensor, a digital motion sensor can be considered, which in particular accomplishes a switchover between various programmed time range or integration limits and/or a corresponding switchover of the processing characteristic (characteristic curve) of the rate determining device.
In a further specialized embodiment, the rate determining device includes a differential member that has a data input for the impedance value, with which very long changes in impedance can be rendered inoperative for the pacemaker control. As a result—with drastically reduced calculation effort and current consumption—a similar effect is attained to that accomplished with the carrying over of the impedance resting curve.
In an expedient further development, the differential member has a time constant control input connected to the sensor for the activity variable, by way of which input the differential time is set to a value
Biotronik Mess-und Therapiegeraete GmbH & Co. Ingenieurbuero Ber
Evanisko George R.
Kamm William E.
Kinberg Robert
Venable
LandOfFree
Rate adaptive pacemaker does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Rate adaptive pacemaker, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Rate adaptive pacemaker will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2550425