Surgery: light – thermal – and electrical application – Light – thermal – and electrical application – Electrical therapeutic systems
Reexamination Certificate
1999-10-06
2002-12-03
Schaetzle, Kennedy (Department: 3762)
Surgery: light, thermal, and electrical application
Light, thermal, and electrical application
Electrical therapeutic systems
C607S018000
Reexamination Certificate
active
06490485
ABSTRACT:
TECHNICAL FIELD
The invention relates generally to a system for processing sensor input and modifying output mapping and particularly, but not by way of limitation, to methods and apparatus for rate-adaptive pacing responsive to physiologic sensor input.
BACKGROUND
Many control systems rely on an output mapping to convert a measured control input to a desired control output. The output mapping is a graphical, tabular or other mathematical function of control output versus control input. As an example, a burner system with fuel and oxygen feeds may measure fuel feed rate as a control input and utilize output mapping to define the desired oxygen feed rate as a control output. The output mapping of oxygen feed rate versus fuel feed rate may not be linear, e.g., requiring increasing levels of excess oxygen at higher fuel feed rates to provide efficient burning of the fuel. Another example of control systems utilizing output mapping are some cardiac rhythm management systems.
Cardiac rhythm management systems include, among other things, pacemakers, also referred to as pacers. Pacemakers deliver timed sequences of low energy electrical stimuli, called pace pulses, to the heart, such as via a transvenous leadwire having one or more electrodes disposed in the heart. Heart contractions are initiated in response to such pace pulses. By properly timing the delivery of pace pulses, the heart can be induced to contract in proper rhythm, greatly improving its efficiency as a pump. Pacemakers are often used to treat patients with bradyarrhythmias, that is, hearts that beat too slowly, or irregularly.
There exists a class of pacemakers known as variable rate or rate-adaptive pacemakers which include a physiologic sensor indicative of metabolic demand and a variable rate pulse generator responsive to changes in metabolic demand. Some physiologic sensors for determining metabolic demand include minute ventilation (MV) sensors for measuring trans-thoracic impedance variations and generating an output signal varying as a function of the patient's minute ventilation, and accelerometers for measuring body vibration during physical activity and generating an output signal varying as a function of the patient's movement. Accelerometers are typically filtered and processed such that the resulting output signal is indicative of the patient's exercising activity, and not of external vibration sources or internal noise. Other physiologic sensors are known in the art, e.g., blood pH, blood temperature, QT interval, blood oxygen saturation, respiratory rate and others.
Rate-adaptive pacemakers attempt to pace a patient's heart at a rate corresponding to the patient's metabolic demand. They accomplish this by utilizing an output mapping to convert a given sensor input to a unique output signal level. It is difficult to predict an appropriate pacing function capable of generating a paced rate corresponding to a patient's metabolic demand at the time of implanting the pacemaker in the patient. To compensate for this deficiency, rate-adaptive pacemakers may incorporate logic to adjust the output mapping by comparing the patient's average maximum sensor-indicated heart rate (AMSIR) to a sensor target rate (STR) at a prescribed or predetermined level of exercise activity. If the patient's actual or demonstrated activity level differs from the predetermined activity level, the adjusting logic may inappropriately adjust the pacing function, resulting in a paced rate that is too high or too low for a given metabolic demand. If the paced rate is too high, the patient may feel palpitated or stressed. If too low, the patient may feel fatigued, tired or dizzy.
As will be seen from the above concerns, there exists a need for an improved method of adjusting output mapping in response to demonstrated sensor input. The above-mentioned problems with matching pacing to a patient's metabolic demand and other problems are addressed by the present invention and will be understood by reading and studying the following specification.
SUMMARY
One embodiment includes a method of adjusting an output mapping of a control output versus a control input. The method includes obtaining signal input data and generating historical signal input data from the signal input data, wherein the historical signal input data is indicative of a breadth and/or frequency of the signal input data in excess of a reference value. The method further includes adjusting the output mapping in response to the historical signal input data. In another embodiment, the method includes increasing an area of the output mapping in response to increasing values of the breadth and/or frequency of the signal input data in excess of the reference value. In a further embodiment, obtaining signal input data includes obtaining data from the control input and/or from one or more auxiliary inputs.
A further embodiment includes a method of adjusting an output mapping of a control output versus a control input. The method includes obtaining signal input and generating historical signal input data. The method still further includes generating a first factor indicative of a breadth of the historical signal input data in excess of a reference value, generating a second factor indicative of a frequency of the historical signal input data in excess of the reference value, and adjusting the output mapping in response to the first and second factors. In a still further embodiment, adjusting the output mapping further includes increasing an area of the output mapping in response to increasing values of the first factor and decreasing the area of the output mapping in response to decreasing values of the first factor. In yet another embodiment, adjusting the output mapping further includes increasing an area of the output mapping in response to increasing values of the second factor and decreasing an area of the output mapping in response to decreasing values of the second factor. In a further embodiment, obtaining signal input data includes obtaining data from the control input and/or from one or more auxiliary inputs.
Yet another embodiment includes a method of adjusting a rate-adaptive curve for pacing a patient's heart. The method includes sensing the patient's activity, thereby producing sensed activity data, generating a demonstrated activity level from the sensed activity data, and adjusting the rate-adaptive curve in response to the demonstrated activity level relative to a predetermined activity level. In one embodiment, sensing the patient's activity further includes receiving input from at least one physiologic sensor. In another embodiment, sensing the patient's activity further includes receiving input from at least one physiologic sensor including minute ventilation sensors and/or accelerometers. In a further embodiment, adjusting the rate-adaptive curve further includes increasing the rate-adaptive curve when the demonstrated activity level exceeds the predetermined activity level and decreasing the rate-adaptive curve when the demonstrated activity level is less than the predetermined activity level. In a still further embodiment, the predetermined activity level corresponds to a prescribed exercise level and frequency.
One embodiment includes a method of adjusting a rate-adaptive curve for pacing a patient's heart. The method includes sensing the patient's activity having an exertion level, generating a factor indicative of a breadth of the patient's exertion levels above a predetermined exertion level, and adjusting at least a portion of the rate-adaptive curve in response to the factor. In another embodiment, the factor increases for increasing breadth of the patient's exertion levels above the predetermined exertion level.
Another embodiment includes a method of adjusting a rate-adaptive curve for pacing a patient's heart. The method includes sensing the patient's activity having an exertion time at an exertion level, generating a factor indicative of a frequency of the p
KenKnight Bruce H.
Lang Douglas J.
Sun Weimin
Cardiac Pacemakers Inc.
Droesch Kristen
Schaetzle Kennedy
Schwegman Lundberg Woessner & Kluth P.A.
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