Surgery – Truss – Pad
Patent
1991-03-15
1993-06-01
Kamm, William E.
Surgery
Truss
Pad
A61N 1365
Patent
active
052150844
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a physiologically operational, rate-adaptive cardiac pacemaker.
Such cardiac pacemakers are for example known from U.S. Pat. No. 4,140,132 and European Patent Application No. 0 080 348. The described cardiac pacemaker comprises an activity sensor which detects the intensity of movement of the patient. An evaluation circuit measures the output signal of a bending vibrator and evaluates the spectral peaks which are created by an activity of the patient above a defined programmable predeterminable threshold. The basic pacing rate of the cardiac pacemaker is varied in accordance with these detected activity levels which change together with each activity of the patient and--in the case of a demand pacemaker--the escape sequences of the pacemaker are also varied between the predetermined minimum and maximum values.
The known cardiac pacemakers have the disadvantage that the rate of change of the stimulation rate is only dependent on the number of the signals received which characterize the activity of the patient and do not provide any information about the signal intensity. For example, when the patient moves by walking, only the step speed `ut not the step intensity can be measured, so that the difference between an exhausting jog with a larger step length and a walk at the same step speed but with a smaller step length cannot be determined.
SUMMARY OF THE INVENTION
The object of this invention is to provide an implantable cardiac pacemaker which can evaluate a basic stimulation rate (an escape sequence in the case of demand stimulation) from the output signal of a bending vibrator which is closely related to the actual physiological needs of the patient.
This object is achieved by the characteristics set out in claim 1. Advantageous features of the invention are set out in the dependent claims.
The invention is based on the realization that an evaluation of the amplitude values of the impulse signals created by the bending vibrator above the programmed threshold contains additional information concerning the actual cardiac output requirements of the patient. That means that the output signal, which is derived from the activity signals which are representative for the activity of the patient, is dependent on the amplitude of the impulses above the programmably set threshold. The escape sequence, which is derived from the output signal, is therefore always closely related to the actual physiological needs of the patient.
With the cardiac pacemaker according to the invention, control signals for the stimulation impulses are generated by an evaluation circuit in accordance with the detected patient activity, whereby these stimulation impulses are detected from a weighted time-mean of the relationship between the time a bandwidth-limited momentary sensor output signal remains above and below the threshold value.
In contrast to the band limiting described in EP-A-0 080 348, in which only frequency ranges between 10 and 100 Hz can pass through, a preferred embodiment of the cardiac pacemaker according to the invention uses a band pass filter, which lets those output signals of the sensor through, which are created by the movement of the patient and which lie, in particular, in the frequency range between 2 and 8 Hz.
The weighting factors of the cardiac pacemaker according to the invention, with which the filtered output impulses of the sensor are weighted, are different for the momentary signal levels above and below the predetermined threshold. They are chosen in such a manner that the impulses which are meaned in a later stage form a control signal which lead to a relatively steep-sloped increase of the basic stimulation rate if they exceed the threshold value and which lead, on average, to a flat-sloped decrease of the basic stimulation rate if they fall below the threshold value--whereby the weighting factors are chosen to correspond with the natural physiological conditions in accordance with the increasing cardiac activity due to a bodily load or in acc
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Biotronik
Kamm William E.
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