Surgery: light – thermal – and electrical application – Light – thermal – and electrical application – Electrical therapeutic systems
Reexamination Certificate
1999-06-25
2001-02-27
Getzow, Scott M. (Department: 3737)
Surgery: light, thermal, and electrical application
Light, thermal, and electrical application
Electrical therapeutic systems
Reexamination Certificate
active
06195585
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to implantable medical devices, and more particularly to implantable medical devices that stimulate the neural system (referred to hereafter as a “neural stimulator” or simply as a “stimulator”). Even more particularly, the invention relates to a neural stimulator that measures and collects data resulting from neural stimulation, and transmits the collected data to a processor for analysis, storage, reporting and/or other purposes. The processor that receives the collected data may be at a non-implanted location remote from the stimulator, at an implanted location adjacent the stimulator, or incorporated as additional circuitry within the same implantable housing as the stimulator.
In an implantable medical device, particularly an implantable neural stimulator, there is a need to measure internal voltages, determine electrode impedances, determine output stimulus linearity, sense and measure biological responses to an electrical impulse, as well as to monitor and measure other biological activities that are associated with or occur coincident with the operation of the device.
Disadvantageously, due to the limited power available within an implantable medical device, coupled with the presence of digital and RF noise in or in the near proximity of the device, the design of any monitoring and sensing circuitry within such device must be non-traditional.
For example, in order to measure a biological response to an applied stimulus (i.e., an “evoked response”), there is a need to deal with the presence of the stimulus artifacts which accompany any applied stimulus. Having the capability of sensing and monitoring the evoked response to an applied stimulus provides a very valuable tool for setting the stimulus parameters at an appropriate level for a given patient. However, heretofore there has been little success in sensing the evoked response because it is such a small signal compared to the stimulus artifact.
By way of example, an evoked response within the aural nerve region may only be in the 10 to 500 microvolt (&mgr;v) range. The needed amplification for handling such small signals (which amplification must be on the order of about 1000) makes the amplifier recovery from the artifacts too slow to capture the evoked response, which evoked response onset typically occurs about 30 to 40 microseconds (&mgr;s) after the stimulus is applied.
In U.S. Pat. No. 5,531,774 there is disclosed a multichannel cochlear stimulation system of the type with which the present invention may be used. As shown in the ′774 patent, the system therein disclosed includes both external (non-implanted) and implanted portions. The implanted portion comprises an implantable cochlear stimulator (ICS) integrally attached to a cochlear electrode array. The electrode array includes a multiplicity, e.g., sixteen, spaced-apart electrodes that may be inserted into a human cochlea, any one of which may be activated for application of an electrical stimulus to cochlear tissue. The ICS disclosed in the ′774 patent further includes a back telemetry circuit which allows certain measurements, e.g., voltage levels present within the ICS, or other measured parameters, to be sent back to the external portion of the system. The ICS disclosed in the ′774 patent is incorporated herein by reference.
In U.S. Pat. No. 5,758,651, there is disclosed a system whereby the sensing electrodes are open circuited for a selected period of time following delivery of a stimulus in order to avoid sensing the artifact. Disadvantageously, the selected period of time during which the electrodes are open circuited varies from patient to patient, and may vary for a given patient depending upon other conditions. Further, switching circuitry is required to perform the open-circuiting function, which switching may introduce switching transients and glitches into the signal.
Thus, it is seen that there is a need for monitoring circuitry within an implantable neural stimulator, e.g., an implantable cochlear stimulator, that is able to accurately sense the evoked response in the presence of large stimulus artifacts, which stimulus artifacts typically vary in terms of amplitude and duration.
SUMMARY OF THE INVENTION
The present invention addresses the above and other needs by providing monitoring/measurement circuitry within an implantable stimulator, e.g., an implantable cochlear stimulator, that allows several different analog measurements to be selectively monitored from within the implantable stimulator, including electrode impedance, evoked responses, and the like. Such measurements are processed, as required, digitized, and stored in the implantable stimulator. When needed or upon request, the measured data is telemetered, or otherwise transferred or sent, from the implant device to a remote processing device. The remote processing device is typically an external (non-implanted) programmer device and/or personal computer (PC). However, it is to be understood that the remote processing device may also comprise an implantable processor that is electrically coupled with the implantable stimulator (e.g., as in the case of a fully implantable cochlear stimulator system of the type disclosed in U.S. patent application Ser. No. 09/126,615, filed Jul. 31, 1998; or Ser. No. 60/108,923, filed Nov. 17, 1998; both of which applications are incorporated herein by reference); or a processor that comprises additional circuitry housed within the same implantable housing as the implantable stimulator (e.g., as in the case of a single package, fully implantable processor/stimulator). Storage of the data in the implantable stimulator further allows the memory within the implantable stimulator to act as a buffer so that data obtained in real-time at a rapid rate can be transmitted to the remote processor at a slower rate, commensurate with the bandwidth of the telemetry or other data link.
In accordance with an important aspect of the invention, all signal activity associated with an applied stimulus, including the artifact, the evoked response and/or the compound action potential (CAP), may be sensed, monitored, preliminarily processed, and stored in real time using circuitry contained within the implantable stimulator; and then subsequently telemetered or sent to a remote signal processing device. The remote signal processing device may then apply additional processing to the received data, including removal of the artifact from the evoked response or CAP, thereby allowing the evoked response and/or CAP to be analyzed, and/or used as feedback information to assist in setting of the stimulus parameters.
In accordance with another aspect of the invention, the measuring/monitoring circuitry of the present invention includes two-level multiplexing of analog signals. Advantageously, two levels of analog multiplexing allow a low power mode for performing frequent measurements with rapid ON/OFF capability, and a high performance mode for performing less frequent Evoked Potential and other electrode-related measurements.
In order to reduce the static power consumption of the measuring/monitoring circuitry of the present invention, it is a feature of the invention that each block in the measuring/monitoring circuitry may be selectively turned OFF or powered down.
The measuring/monitoring circuitry of the invention includes a first analog multiplexer (MUX) connected to a gain controlled, low noise, differential amplifier. The output of the differential amplifier is coupled to a second analog MUX along with other analog signals, e.g., operating or bias voltages used within the device. The signal appearing at the output of the second analog MUX is preliminary processed as required, e.g., to adjust the amplitude (attenuate) and/or filter out high frequency components. Once processed, the signal is then presented to an analog-to-digital (A/D) converter where it is sampled at a specified rate and digitized. The digitized signal is then stored in memory, and eventually transmitted to a remote, e.g., non
Finley Charles C.
Karunasiri Rankiri Tissa
Advanced Bionics Corporation
Getzow Scott M.
Gold Bryant R.
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