Surgery: light – thermal – and electrical application – Light – thermal – and electrical application – Electrical therapeutic systems
Reexamination Certificate
1999-02-04
2001-09-11
Layno, Carl H. (Department: 3762)
Surgery: light, thermal, and electrical application
Light, thermal, and electrical application
Electrical therapeutic systems
C607S012000, C607S034000, C607S029000
Reexamination Certificate
active
06289246
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention pertains to a neural or muscular tissue stimulating prosthesis capable of delivering a high current stimulation signal to a nerve, or brainstem, of a patient and, more particularly, to a cochlear prosthesis with a power supply having an output which can be selectively boosted to a high level.
2. Description of the Prior Art
Though the subject invention will find application with many types of tissue stimulating device it will be described in relation primarily to cochlear prosthesis systems. These prostheses are used to provide therapy to patients suffering from certain hearing impairing conditions. Frequently such systems are of a “two-part” design in that they comprise two sections: an internal or implanted section, and an external section. The external section includes a microphone for receiving ambient sounds and converting them to electrical signals. Power to the external section is provided by a battery. The electrical signals are processed and sent to the implanted section. The implanted section then generates excitation signals to excite the aural nerve of the patient by means of appropriately positioned stimulation electrodes.
Most commonly, the external section of a two-part cochlear prosthesis is inductively coupled by a transcutaneous RF link to the implanted section. The energy of the electrical signals in the RF frequency range is rectified and stored by a power supply located in the internal section. It is that power supply which provides the energy required to power the internal section and to generate the stimulus signals.
More recently there has been a trend in cochlear prosthesis design towards the use of totally implantable prostheses. In such devices the entire cochlear prosthesis, including a battery, is implanted. Obviously it is highly desirable that a totally implanted cochlear prosthesis be of as small a size as possible. In order to achieve the necessary miniaturisation it is important that the power supply, and so by necessity the battery, be of a small size.
To minimise the power requirements of the implanted section of a cochlear prosthesis, whether it be of the totally implanted or of the two-part type, it is desirable to operate it at as low a voltage as possible. One problem however with this approach is that a minimised voltage may present difficulties for the circuitry which is to apply the stimulation currents. In particular, a low operating voltage has hitherto reduced the maximum available amplitude of the stimulating signals that may be generated. An undesirable result is that the dynamic range of the stimulation signals conveyed to the patient is reduced so that loud sounds are perceived by the patient as being quieter than they should be.
Another problem, which is relevant only to cochlear prostheses of the two-part type, is that power supply voltage within the internal section is sensitive to the relative position and spacing of the coils used for the inductive coupling of the internal and external sections. When this positioning is not correct, the intercoil coupling is not optimal, and therefore the available power in the implanted section drops resulting in a limitation of the amplitude of the stimulation current that can be generated into the electrodes.
The problem of insufficient power being available to deliver the appropriate stimulations is especially acute for cochlear prostheses using biphasic stimulation current pulses. These pulses consist of two consecutive phases of opposite polarities with the first phase having a higher peak voltage amplitude than the second phase, due to the capacitive component of the load. If the power supply for the internal section has an inadequate voltage level (i.e., the power supply has a compliance problem), the current during the first phase of a pulse is smaller than required while the current during the second, lower voltage phase, remains unchanged thereby resulting in an unbalanced stimulation pulse.
In order to resolve these problems it has been proposed that, when sufficiently high voltage levels are not available, the duration of the biphasic pulse be increased to compensate, so that the charge delivered during each current phase remains approximately constant. However, the use of longer stimulation pulses inherently reduces the maximum stimulation rate of the device and so is undesirable.
OBJECTIVES AND SUMMARY OF THE INVENTION
In view of the above-named disadvantages of the prior art, it is an objective of the present invention to provide a tissue stimulating system with improved power supply in order to eliminate non-compliant episodes, i.e. episodes in which stimulation pulses are applied which are of less-than-desired current.
A further objective is to provide a tissue stimulating system which selectively increases the voltage available to the stimulation electrodes to a level sufficient to provide suitable cochlear stimulation.
Other objectives and advantages of the invention shall become apparent from the following description.
In particular, a cochlear prosthesis system constructed in accordance with this invention includes a means for receiving and processing ambient sounds to generate processed signals which are applied to the aural nerve through an electrode array. Importantly, the generation of the output signal being delivered to an electrode is monitored and if it is determined to be insufficient a voltage multiplier scheme is used to boost the voltage of the power supply to a high level temporarily, thereby ensuring that the output current can reach the required value.
According to a first aspect of the invention there is provided a tissue stimulating system of the type wherein a power supply and at least one programmable current source are provided for generating a stimulation current of predetermined amplitude, said system further comprising:
a booster circuit for selectively boosting the supply voltage of said power supply when said supply voltage is insufficient to allow said current source to provide a predetermined stimulation current.
According to another aspect of the invention there is provided a cochlear prosthesis system including:
a microphone for picking up ambient sounds;
signal processing circuitry coupled to the microphone for determining stimulation signals corresponding to said ambient sounds;
an electrode array for applying said stimulation signals to the nervous system of a patient;
a power supply for providing energy for the generation of said stimulation signals;
an energy storage device arranged and constructed to selectively supplement said power supply;
a sensor for monitoring the generation of said stimulation signals to determine if said power supply requires supplementation by said energy storage device in order to enable generation of said determined stimulus signals; and
a multiplier switching circuit for selectively switching said energy storage device so that it supplements the voltage provided by the power supply in order to ensure that stimulation signals as determined by the signal processor are generated.
Finally, according to yet another aspect of the invention there is provided a method for improving the compliance of the stimulation current output stage of a tissue stimulating system, said output stage including at least one programmable current source and power supply, said method including the steps of:
a) determining if the voltage across each said current source is sufficient to allow generation of a stimulation current of desired amplitude;
b) in the event that said voltage is determined to be insufficient in step a), placing a charged energy storage device in series with said power supply so as to increase the potential voltage across each said programmable current source.
REFERENCES:
patent: 4141064 (1979-02-01), Nagashima
patent: 4792886 (1988-12-01), Sahm
patent: 5372605 (1994-12-01), Adams et al.
patent: 5387228 (1995-02-01), Shelton
patent: 5391191 (1995-02-01), Holmstrom
patent: 5522865 (1996-06-01), Schulman et al.
patent: 5869970 (1999-02-01), Pal
Cochlear Pty. Ltd.
Gottlieb Rackman & Reisman P.C.
Layno Carl H.
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