Surgery: light – thermal – and electrical application – Light – thermal – and electrical application – Electrical therapeutic systems
Patent
1999-06-24
2000-03-28
Getzow, Scott M.
Surgery: light, thermal, and electrical application
Light, thermal, and electrical application
Electrical therapeutic systems
A61N 1365
Patent
active
060442999
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an implantable medical device, such as an implantable heart stimulator, of the type containing an accelerometer for detecting mechanical vibrations conducted by tissue in the vicinity of the implanted device.
2. Description of the Prior Art
From U.S. Pat. No. 4,140,132 a variable rate pacemaker is known having a piezo-electric element which, when subjected to motion, vibrates due to the resulting strain upon it to provide alternating voltage. Said voltage is used for varying the rate of the pacemaker which consequently is varied in response to the physical activity of the pacemaker patient.
Pacemakers commonly uses electrodes for sensing electrical signals related to heart activity. Alternatively a pacemaker may use sounds related to heart activity for monitoring heart activity. U.S. Pat. No. 5,447,523 discloses a pacemaker including a microphone for sensing acoustic heart signals. The microphone includes a sensor responsive to relative movement between two portions of the pacemaker housing caused by heart movements. The sensed signals are filtered and systolic time intervals (STI) are extracted from it. The systolic time intervals are used as reference quantities for the stimulation pulse rate. The amplitude of the detected sound signal is small since only the difference in movement between the two housing portions is detected. The quality of the sensed sound signal varies from patient to patient depending on the bodily constitution of the patient. These limitations need to be considered when using this prior art sensor signal for controlling a pacemaker. Furthermore, the systolic time intervals suffer from lack of sensitivity as control parameters for a pacemaker.
SUMMARY OF THE INVENTION
A primary object of the invention is to solve the abovementioned problem that the quality of the sensed sound signal varies from patient to patient depending on the bodily constitution of the patient.
A second object is to solve the abovementioned problem related to the fact that the systolic time intervals suffer from lack of sensitivity as control parameters for a pacemaker.
A third object of the present invention also relates to the problem of providing a heart stimulator having means for generating suitable stimulation signals without the need for electrodes for electrically sensing heart activity.
The above objects are achieved in accordance with the principles of the present invention in an implantable medical device having an accelerometer mounted in an implantable housing, the accelerometer detecting vibration of the housing and generating a vibration signal in response to those vibrations, and having a signal processor contained in the housing which is supplied with the vibration signal and which generates, for a number of predetermined frequency ranges, respective parameter values which are indicative of a predetermined attribute of the vibration signal, and the signal processing unit calculates a ratio of any two of these parameter values and emits, dependent on the ratio, at least of a number of predetermined status values respectively indicating different predetermined cardiac activities.
Thus, according to the inventive device a status value related to heart activity is established as a quotient i.e., a ratio between two parameter values. The establishing of quotients leads to elimination of the disadvantageous dependence of measured values on the bodily constitution of the patient. Furthermore the quotient values are less dependent on the position of the patients body than are the parameter values as such.
According to a preferred embodiment of the device according to the invention the sensor signal is generated by a sensor means including an accelerometer having a primary direction of sensitivity substantially perpendicular to the plane of the disc shaped housing of the implantable device. This leads to an advantageously high sensitivity to heart vibrations, when the device is implanted in a subject's body as the d
REFERENCES:
patent: 4140132 (1979-02-01), Dahl
patent: 5383473 (1995-01-01), Moberg
patent: 5447523 (1995-09-01), Schaldach
patent: 5496352 (1996-03-01), Renger
patent: 5649968 (1997-07-01), Alt et al.
Getzow Scott M.
Pacesetter AB
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