Circuits and methods for using a high impedance, thin, coin-cell type battery in an implantable electroacupuncture device

1. An implantable electroacupuncture device (IEAD) adapted to generate and apply electrical stimulus pulses to a target tissue location of a patient when the IEAD is implanted above the target tissue location, the IEAD comprising:

a thin, disc-shaped, hermetically-sealed case having a front side, a back side, and an edge side, the edge side joining the front side to the back side around the perimeter of the sealed case, the front and back sides having a longest linear dimension D2 that is no greater than about 25 mm, and the edge side defining an overall thickness or width W2 of the disc-shaped case to be no greater than about 2.5 mm;

an anodic electrode and a cathodic electrode secured to an outside surface of the thin, disc-shaped, hermetically-sealed case, wherein the cathodic electrode comprises a central electrode located substantially in the center of the front side of the disc-shaped case, and wherein the anodic electrode comprises an annular ring electrode concentric with and located around and at least 5 mm distant from the closest point of the central electrode;

electronic circuitry housed within the thin, disc-shaped, hermetically-sealed case that causes electrical stimulus pulses to be generated and applied to the central cathodic electrode and the anodic annular ring electrode in accordance with a prescribed stimulation regimen:

feed-through means for electrically connecting the electronic circuitry on the inside of the hermetically-sealed case to the concentric electrodes on the outside of the hermetically-sealed case, wherein the concentric configuration of the electrodes on the front side of the disc-shaped case causes electrical stimuli to flow between the anodic annular ring electrode and the cathodic electrode as steered by electric field gradient lines that are strongest along an acupoint axis line that extends perpendicularly out from the central cathodic electrode on the front side of the disc-shaped case, whereby the electrical stimuli is guided to the target tissue location along the acupoint axis line and at a tissue depth below the location of the central cathodic electrode on the front side of the disc-shaped case; and

a thin, coin-cell type primary battery on the inside of the thin, disc-shaped, hermetically sealed case connected to the electronic circuitry that provides operating power for the electronic circuitry, the coin-cell primary battery having a nominal output voltage of V BAT volts, where V BAT ranges from as low 2.2 volts to as high as 3.6 volts;

wherein the primary battery has an internal impedance greater than 5 ohms; and

wherein the electronic circuitry includes power management circuitry that limits the amount of instantaneous current that can be withdrawn from the battery; and

wherein the prescribed stimulation regimen causes electrical stimulus pulses to be generated and applied only during a stimulation session having a duration of T3 minutes, wherein T3 is at least 10 minutes, and wherein the time interval between stimulation sessions is T4 minutes, and wherein the ratio of T3/T4 is no greater than 0.05.

2. The IEAD of claim 1 wherein the electronic circuitry includes:

a boost converter circuit (U 1 ) that boosts the battery voltage V BAT to an output voltage V OUT , where V OUT is at least 3 times V BAT and no more than 8 times V BAT ;

a microcontroller circuit (U 2 ) powered by VBAT that controls the operation of the electronic circuitry so that the stimulus pulses are generated at a specified amplitude in accordance with the prescribed stimulation regime;

a programmable current source circuit (U 3 ) that sets the amplitude of the current in the stimulus pulses to a desired level;

a sensor circuit (U 4 ) adapted to receive external commands from an external control device that provide operating commands or parameters for the microcontroller circuit, the operating commands including ON/OFF commands, and the operating parameters including defining the time T3, the time T4, and the stimulus amplitude;

an electronic switch (U 5 ), controlled by the microcontroller circuit, that switchably applies the programmed current to the central cathodic electrode and the anodic annular ring electrode so that when the IEAD is implanted in the patient such switching is adapted to cause the programmed current to flow through the patient's body tissue towards the specified target tissue location.

3. The IEAD of claim 2 wherein the microcontroller circuit includes means for controlling the operation of the boost converter circuit in a way that limits the amount of instantaneous current that can be drawn from the battery, thereby preventing the battery voltage V BAT from dropping to values that would prevent the electronic circuitry from operating.

4. The IEAD of claim 3 wherein the means for controlling the operation of the boost converter circuit in a way that limits the amount of instantaneous current that can be drawn from the battery comprises duty-cycle modulating the boost converter circuit with a digital control signal that causes the boost converter circuit to switch between an ON state for a short time and to an OFF state for a long time, the ratio of the ON time to the OFF time being less than 0.02.

5. The IEAD of claim 2 wherein the boost converter circuit automatically shuts down whenever the battery voltage V BAT drops below a fixed threshold, wherein the battery voltage below the fixed threshold is still sufficiently high to permit operation of the microcontroller circuit, and wherein the automatic shutting down of the boost converter circuit significantly decreases the current being drawn from the battery, whereby due to the high internal resistance of the battery the battery voltage increases when the boost converter circuit shuts down and decreases when the boost converter circuit is ON, thereby causing the boost converter circuit to automatically switch between an ON state and an OFF state, which switching limits the amount of current that can be drawn from the battery.

6. The IEAD of claim 5 wherein the nominal battery voltage is 3 volts, and the fixed threshold below which the boost converter circuit shuts down is 2.5 volts.

7. The IEAD of claim 5 wherein the electronic circuitry further includes means for kick starting the programmable current source when the stimulus current amplitude is less than about 2 mA, which kick starting has the effect of driving the programmable current source directly from the microcontroller circuit at the beginning of the stimulus pulse, which action shortens a delay associated with starting the operation of the programmable current source at low current amplitudes by at least a factor of about 5.

8. The IEAD of claim 5 wherein the electronic circuitry further includes a cascode circuit (Q 1 ) connected to the input terminal of the programmable current source circuit (U 3 ), which cascode circuit is adapted to significantly reduce the input capacitance looking into the cascode circuit over the capacitance that is seen looking into the input terminal of the programmable current source, wherein transient signals appearing at the leading edge of the stimulus pulse are significantly reduced.

9. The IEAD of claim 1 wherein the anodic annular ring electrode resides on the perimeter edge side of the thin, disc-shaped case.

10. A leadless, implantable, electroacupuncture device (IEAD) adapted to generate and apply electrical stimulus pulses to a target tissue location of a patient when the IEAD is implanted below the skin of the patient so as to be near, but not on, the target tissue location, the IEAD comprising:

a thin, disc-shaped, hermetically-sealed case having a front side, a back side, and an edge side, the edge side joining the front side to the back side around the perimeter of the sealed case, the front and back sides having a longest linear dimension D2 that is no greater than about 25 mm, and the edge side defining an overall thickness or width W2 of the disc-shaped case to be no greater than about 2.5 mm;

a central electrode located substantially in the center of the front side of the disc-shaped case, and an annular ring electrode that surrounds the central electrode and is spaced at least 5 mm distant from the closest point of the central electrode;

electronic circuitry housed within the thin, hermetically-sealed case that causes electrical stimulus pulses to be generated and applied to the central electrode and the annular ring electrode in accordance with a prescribed stimulation regimen and polarity, wherein the polarity of the central electrode is one polarity at the same time that the polarity of the annular ring electrode is an opposite polarity;

feed-through means for electrically connecting the electronic circuitry on the inside of the hermetically-sealed case to the central and annular ring electrodes on the outside of the hermetically-sealed case, wherein the configuration of the electrodes on the front side of the disc-shaped case causes electrical stimuli to flow between the annular ring electrode and the central electrode as guided by electric field gradient lines that are strongest along an acupoint axis line that extends perpendicularly out from the central electrode on the front side of the disc-shaped case, and wherein the electrical stimuli is guided to the target tissue location along the acupoint axis line at a distance d2 below a surface of the patient's skin; and

a thin, coin-cell primary battery on the inside of the thin, disc-shaped, hermetically sealed case connected to the electronic circuitry that provides operating power for the electronic circuitry, the thin, coin-cell primary battery having an initial internal impedance greater than 5 ohms, and which internal impedance increases over time and usage to 150 ohms or more; and

wherein the electronic circuitry includes power management circuitry that limits the amount of instantaneous current that can be drawn from the primary battery so that the IEAD continues to operate in accordance with the prescribed stimulation regimen for at least two years; and

wherein the prescribed stimulation regimen causes electrical stimulus pulses to be generated and applied only during a stimulation session having a duration of T3 minutes, wherein T3 is at least 10 minutes, and wherein the time interval between stimulation sessions is T4 minutes, and wherein the ratio of T3/T4 is no greater than 0.05.

11. The leadless IEAD of claim 10 wherein the central electrode is configured to function as a cathode electrode, and the annular ring electrode that surrounds the central electrode is configured to function as an anode electrode.

12. The leadless IEAD of claim 10 wherein the annular ring electrode that surrounds the central electrode is positioned on an outside surface of the perimeter edge side of the disc-shaped case.