WO2003105492A2

WO2003105492A2 - Method of data communication with implanted device and associated apparatus

Info

Publication number: WO2003105492A2
Application number: PCT/US2003/016696
Authority: WO
Inventors: Mingui Sun; Robert J. Sclabassi; Marlin H. Mickle
Original assignee: University Of Pittsburgh Of The Commonwealth System Of Higher Education
Priority date: 2002-06-06
Filing date: 2003-05-28
Publication date: 2003-12-18
Also published as: US7228183B2; WO2003105492A3; US20040199222A1; AU2003237263A1; AU2003237263A8; US20030229382A1; US6847844B2

Abstract

The present invention provides a method of communicating data employing current pulses transmitted by an implanted device through living biological tissue to an external device. The method also contemplates transmission of current pulses from the external device through living biological tissue to an implanted device. Uniquely configured antenna electrodes are preferably employed in the implanted device. Increase in signal-to-noise ratio is achieved through synchronization. The method may be employed in diagnostic, therapeutic and general monitoring activities in connection with human beings. Corresponding apparatus is disclosed.

Description

METHOD OF DATA COMMUNICATION WITH IMPLANTED DEVICE AND

ASSOCIATED APPARATUS

STATEMENT OF GOVERNMENT INTEREST

The United States Government has rights under this invention pursuant to Grant 1-

R01-NS43791 from the National Institutes of Health.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method and associated apparatus employed in

wireless two-way communication of data by means of current pulses traveling through

living biological tissues and, more specifically, it contemplates the use of an implantable

device which may be implanted, for example, in a patient's brain, torso or abdomen in

cooperation with an external computerized device for diagnostic, monitoring or therapeutic

purposes.

2. Description o the Prior Art

The value of using invasive procedures and devices in diagnosing, monitoring or

treating patients has long been known in the medical environment. It has been known, for

example, to employ a pacemaker for regulating heart functions. Also, deep brain electrical

stimulation for the treatment of Parkinson's Disease has been known.

It has also been known to suggest the use of implantable devices which are in

communication with an external computerized device, such as by radio frequency (RF)

signals or light or wired connection, for example. It has also been known for various purposes to suggest two-way communication with wireless base and remote stations wherein data may be communicated. See, for

example, U.S. Patent 6,289,237.

Among the problems with the prior art utilizing wired systems are the risk of infection and reduced mobility of the patient.

Among the problems with prior art RF systems have been the requirement for

substantial size, difficulty in recharging batteries and signal-to-noise ratio. Also the energy

required to convert between the signal and the RF waves can be substantial.

There remains, therefore, a substantial need for an implantable device which will

efficiently and accurately receive signals from an external device and deliver signals to the

external device for medical diagnosis, monitoring and therapeutic purposes.

SUMMARY OF THE INVENTION

The present invention has met the above-described need. In the method of the present invention, an implanted device has a first antenna having a pair of electrodes and

associated first circuit components. An external device has a second antenna having a pair of electrodes and an associated microprocessor. The invention involves transmitting

current pulses containing data through living biological tissue, thereby taking advantage of

the electrical conductivity of the ionic fluid of such biological tissue. The data transmission

may be effected in both directions, i.e., from the external device to the internal device and

from the internal device to the external device. The transmissions are preferably synchronously effected. Corresponding apparatus is provided. ^'

A unique construction of first or volume conduction antenna facilitates directional

delivery of the information with high efficiency in the far field. The efficiency of data communication is such as to enhance battery life. The system

also facilitates miniaturization, including the use of microchip technology.

It is an object of the present invention to provide a method and associated apparatus

for providing efficient communication between an implanted device and an external device

for purposes of data transmission employing volume conduction.

It is another object of the present invention to provide such a system which can be

miniaturized and make efficient use of energy employed to power the system.

It is a further object of such an invention which facilitates implantation of the

implantable device in a human patient in regions such as the brain, torso or abdomen.

It is yet another object of the present invention to provide such a system which does

not require the use of wires for purposes of power delivery or data transmission or the use

of light, magnetic field, ultrasound or RF energy.

It is a further object of the present invention to provide such a system which takes

advantage of the electrical current carrying capabilities of the body's ionic fluid in order to

employ the same as an information carrier.

It is yet another object of the present invention to provide such a system which

facilitates efficient synchronous communication of current pulses through living biological

tissues.

These and other objects of the invention will be more fully understood from the

following detailed description of the invention on reference to the illustrations appended

hereto.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a schematic illustration showing the general interaction between the

implantable device and the external device. Figure 2 is a schematic illustration of a human patient.

Figure 3 is an illustration of a passive two-port system illustrating the reciprocity

theorem.

Figure 4 is a perspective view of a form of preferred volume conduction antemia of

the present invention.

Figure 5 is an end elevational view of the volume conduction antenna of Figure 4.

Figure 6 is a left side elevational view of the antenna as shown in Figure 5.

Figure 7 illustrates a prior art form of dipole antenna and the corresponding current field.

Figure 8 illustrates a preferred form of volume conduction antenna of the present

invention and its associated current flow.

Figure 9 illustrates schematically a preferred form of synchronizing the

communication of the present invention with the heart action as monitored through an electrocardiogram. Figures 10(a) and 10(b) illustrate schematically the external and internal device

functioning in the context of Figure 9.

Figure 11 illustrates a form of implantable brain chip design with a first antenna of

the present invention having a pair of electrodes.

Figure 12 illustrates schematically functioning of the electrodes of Figure 11.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As used herein, the term "volume conduction" means data communication by

wireless passage of data by current pulses passing through living biological tissues between an implanted device and an external device. As used herein, the term "patient" means a member of the animal kingdom, including human beings.

As employed herein, the term "current pulse(s)" means electrical current waveforms

which have been modified to carry information such as by, for example, phase shift keying,

amplitude modulation or frequency modulation.

The present invention makes advantageous use of an implanted device having a first

antenna having a pair of electrodes for receiving and transmitting current pulses from and

to an external device having a second antenna having a pair of electrodes and employing the external second antenna to deliver and receive current pulses to and from the implanted first antenna. Each antenna is associated with a microprocessor and related circuit components.

The use of suitably processed current to deliver pulsed current information

eliminates a number of the aforementioned problems. In the present context, passage of the current pulses which may be made to contain the desired information as by modulation through living biological tissues takes advantage of the fact that ionic fluid in biological tissues conducts electric current efficiently. This, therefore, prolongs the life of and reduces the size of any battery that would be employed in the implantable device. It also

eliminates the need for conversion of light, sound, or RF signals to digital signals for

purposes of data communication.

This further permits miniaturization which facilitates the use of microelectronic chips, as in implantable brain devices of the present invention.

Referring to Figure 1 , there is shown a segment of living biological tissue 2 such as

provided in a patient and skin 4 disposed exteriorly thereof. An internal volume conduction

first antenna 8 is in intimate contact with the living biological tissue 2 and is operatively associated with circuit components 10 which may be energized by battery 12 or another device that produces electrical current. The implanted antenna 8, circuit components 10 and battery 12 may all be provided within a single housing (not shown) which may be

suitable protectively encapsulated within a biocompatible resinous material such as epoxy or

other synthetic material having the desired durability, sealing properties and inertness. The

external second antenna 20 is in operative association with a microprocessor 22 which is energized by a suitable power source, which may be a suitable battery 24.

In general, the system, in a manner to be described hereinafter in detail,

contemplates two-way communication employing current pulses traveling between the external second antenna 20 and the implanted first antenna 8 in either direction in

synchronized fashion. The circuit components 10 may include sensors to obtain information for delivery to the external device and, where appropriate, actuators and other elements desired for the particular use. The present invention eliminates the need to rely on hard wired systems, transmitted energy as by light, sound, or RF and employs the

biological tissue electric conductivity characteristics to carry current pulses which contain

the desired information.

As shown in Figure 2, a center line of a standing human being has been identified as

30 with the dimension D between the outermost portion of the internal first antenna 8 and the innermost portion of the external second antenna 20 which will generally be in contact

with skin 4 being designated by the letter "D. " In humans, it is presently preferred that the distance "D" be less than about 15 cm. In general, this dimensional preference will be adequate to employ an implanted device within the human brain, torso, or abdomen, as well as other portions of the body, and will be able to communicate with an external device

with adequate signal strength for effective communication. Referring to Figure 3, there is illustrated a linear two-port network N_R with two

different connections. It will be seen that, in accordance with the reciprocity theorem these

portions which are representative of the antennas 8, 20 have port 34 providing a current

source i at terminals 1-1' which produces an open circuit voltage at 2-2' of v. Similarly,

port 36 has a current source i which is identical to that for port 34, but at terminals 2-2'

and produces an open circuit voltage at terminals 1-1' of v' . Under the reciprocity

theorem, v = v' regardless of the topology within N_R. This means that the input and

output of the system can be interchanged without altering the response of the system to a

given waveform. In the present environment this means that reversing the

transmission/reception modes of the internal first volume conduction antenna 8 and the

external second antenna 20 the received, voltage will not vary. As a result, under the same

excitation current, the volume conduction based data communication system produces the

same output regardless of whether the information is flowing from the external device to

the internal device or in the reverse direction.

Referring to Figures 4 through 8, a preferred form of first volume conduction

antenna of the present invention will be considered.

As shown in Figures 4 through 6, the preferred first antenna 40 has a suitable

electrical connection through wires 42, 43 to other circuit components 10 (not shown in this

view) and has a pair of concave shells 44, 46 facing outwardly in generally opposed

directions. Shells 44, 46 have inner generally convex surfaces 50, 52, respectively, which

in the form shown, are joined at 56. The shells are preferably made of a corrosion resistant

metallic or nonmetallic electrically conductive material, such as a suitable metal such as

stainless steel or brass, carbon or a conductive polymer, for example, and have on their

convex surfaces 50, 52 a coating of an electrically insulating material. Referring to the prior art dipole construction shown in Figure 7, a pair of electrical

conductors 60, 62 are positioned in relative spaced relationship and illustrate the current

field exhibited by such construction. This shows that the majority of the current flux goes

directly from the positive pole 60 to the negative pole 62, thereby providing a strong

shorting current which not only wastes power, but also promotes tissue damages at the

source site and other adverse effects which might interfere with a vital organ's activity,

such as cardio-pulmonary, nervous or muscular functions. It is also noted that the use of

far- field components of the antenna field, which contributes the transfer of information, is

relatively weak.

While the individual shells 44, 46 may be symmetrical, in the preferred form of the

invention, the shells 44, 46 are asymmetrical and have the upper portion which may be

considered to be above the horizontal bisector between the lowermost portion and

uppermost of the shell elongated with respect to the lower. This serves to provide the

desired directional transmission.

Also shown in Figure 8 is the fact that the generally x-shaped configuration of the

antenna electrodes, combined with the insulators blocking short circuiting, force the current

to flow around longer paths thereby increasing the far-field as the amount of current

flowing through the conductor volume is the same in both Figures 7 and 8. The flux lines

of the upper portion, as represented by reference number 60 are longer than the flux lines

of the lower portions 62.

The preferred antenna, as shown in Figure 8, will preferably be employed solely in

the implanted first volume conductive antenna 8 and not in the external second antenna 20.

A comparison between the x- shaped electrode pair, as shown in Figure 8, was made with

the known dipole antenna as shown in Figure 7, wherein both antennas had a width of 7 mm. In each instance, the transmitted sinesoidal current signal was 1 KHz and the received

voltage signal by the external electrodes 15 cms from the internal electrodes was measured.

The results are shown in Table 1.

Table 1

The first column shows the received signal strength in mV (peak value) for each three levels. The first column under each antenna heading indicates the required

transmission current inμA (peak value), followed by the transmission voltage in mV (peak

value) and power consumption in μψ. It will be seen that for the same output, the new

antenna required only about 30-35 % of the transmission current, 3-6% of the transmission voltage and 1-2% of the power, as compared with the known prior design as shown in Figure 7. These results confirm the fact that the present invention facilitates

miniaturization, lower power consumption and longer battery life or the use of a smaller

battery or other power source while preserving the desired communication efficiency. Among the enhanced difficulties between the use of an internal device within a

living patient and an external device effecting bi-directional communication therebetween are the fact that in a live biological body, there is a noisy environment due to the ongoing activity of heartbeat, arterial pulses and muscle activity, for example. Also, the internal

and external devices must coordinate their data communication paths so as to provide for

synchronized bidimensional communication while taking advantage of volume conduction characteristics of current pulse flow through live biological tissue. All of this must be accomplished employing an internal device which preferably is of small size, light weight

and watertight.

A preferred way of accomplishing the foregoing in the present invention is to

employ the electrocardiographic (ECG) signal as a clock for synchronization.

Referring to Figure 9, a time frame reference moving horizontally from left to right

is provided graphically. As will be appreciated in the description which follows, use of the

cardiac ECG as a reference, combined with exchange between the internal device and the

external device facilitate: (1) providing efficient communication; (2) eliminating the need

for an external clock mechanism which synchronizes the activities of the implanted device and external device; and (3) maximizing signal-to-noise ratio and, in particular, minimizing

the noisy effect created by the heart pumping and deformation of major arteries.

Referring to Figure 9, there is shown in the uppermost portion, the sharp peaks designated R-waves and shown as "R," with the delta symbol and two-spaced lines

indicating that communication between the external device and internal device will not

occur during that period. As a result of not communicating during the R-wave, this source

of noise which has the potential to interfere with efficient communication between the external device and the internal device is avoided. Underlying the plot of the ECG are the

plots of the external device and the implanted device. The initial Idle Phase has an R-wave

followed by a positive pulse designated "A" which is transmitted by the external device to the implanted device during the idle phase. This current pulse is a request for the implanted device to transmit data. In response, a signal labeled "B" is sent by the

implanted first antenna 8 to the external second antenna 20 (Fig. 1) during the Active Phase. This transmission/reception halts automatically after a certain predetermined period of time. If the data transmission has not been completed, a positive going pulse A is sent

again upon the arrival of the next R-wave by the external device and the process repeats

(not shown). If the external device would like to send commands or instructions to the

internal device, a negative pulse, such as pulse "C" is sent by the external device during the

Idle Phase after an R-wave. The implanted device then switches to the receiving mode and

a signal wave labeled "D" is put on the channel by the external device during the quiescent

period of the ECG in an Active Phase. It will be appreciated that the illustration in Figure

9 is for conceptual purposes and in actual functioning the waveforms "A," "B," "C" and

"D" would be modulated and well defined waveforms suitable for transmission through the

communication channel to take advantage of the volume conduction.

The flow diagrams of Figures 10(a) and 10(b) illustrate schematically flow diagrams

of ways in which the concepts of Figure 9 may be implemented in achieving the objectives

of the present invention. More specifically, in monitoring the heart involvement, the

second antenna has a pair of body surface electrodes 100 which receive the ECG signals

which are amplified at 102 and converted into a digital equivalent at analog-to-digital

converter (A/D) 104, followed by peak detection 110 delayed by the increment delta 112

and generation of signals "A" or "C" 114. The control signal is then introduced into the

transmission/reception antenna electrodes 120 which, depending upon whether it is signal

"B," meaning that it is the implanted device emitting the signal, or signal "D," meaning

that it is the external device emitting the signal, an appropriate position of control switch

132 will be employed. If it is signal "B, " there is amplification 134, analog-to-digital

conversion 136, signal processing 138 in the microprocessor 22 (Fig. 1), demodulation 140

and the emitted biological data 142 which has been communicated. With the signal "D"

emitted by the external device with a command signal 150 passing through the digital logic shaping station 152, followed by modulation 154 and digital-to-analog conversion 156,

amplification 158 and current drive which provides an appropriate amount of power to be

emitted by the skin-surface external electrodes 160.

Referring now to Figure 10(b) and the implanted device, the implanted antenna

shown as 8 in Figure 1 represented by 190 in Figure 10(b) has a system control switch 192,

which, depending upon which of the four signals in the example shown in Figure 9 is being

employed will be in an appropriate position. If the signal is "A" or "C," it is amplified

194, is detected for a "A" or "C" 196, which is subjected to digital logic 198, which, after

a desired delay 200, activates the switch 192. If the signal is "A," biological data 210,

after amplification 212, filtering 220 and modulation 222, all in analog form, are sent to the

electrodes by current driver 224 for transmission through drive signal "B." If the status is

"C," signal "D" is received from the electrodes 190, is amplified 230, demodulated 232

and is converted to appropriate digital form and processed by digital logic 234, after which

the suitable commands/instructions 236 are provided.

If desired, the system may be operated ignoring the peaks of the ECG for a

specified number of R-waves. A further alternative would be to build a buffer and transmit

each packet of data at a faster or slower rate than real-time, as desired for specific

applications..

It will be appreciated that a central benefit of the present invention is the ability to

transmit current pulses efficiently and synchronously through live biological tissues

between implanted and external devices. The reduced size of the unit permits an

encapsulated implantable device employing the benefits of microelectronic chips, for

example, in the brain, torso, or abdomen or other portions of the body. Referring to Figures 11 and 12, examples of a preferred use in respect of the brain

will be considered.

In this embodiment, the implanted device or electronic capsule 270 includes an

electrically insulative material 274 interposed between the electrodes 276, 281 of the first

antenna. The implanted device is positioned on a flexible sheet 272, which may be plastic

with an underlying plurality of subdural electrode contacts shown generally at 277, 280,

282, for example.

In this form of the implanted first antenna, a pair of outwardly concave electrodes

276, 281 are separated by the large electrically insulating element 274 which may contain

or have secured thereto first circuit components. Unlike the embodiment shown in Figures

4-6 and 8, each electrode 276, 281, as viewed from an end such as perpendicular to

electrode 276, for example, will appear to be generally rectangular.

The first antenna assembly may advantageously form part of an electronic chip

which is encapsulated and implanted in the brain region between the skull and the brain.

The flexible, transparent, thin plastic sheet 272 may be provided in a variety of sizes and

shapes. Similar sheets are commercially available for subdural EEG recording during

diagnosis of epilepsy. The connection lead and connector are removed so as to convert this

system from wire transmission to wireless transmission. The first antenna electrode 276,

281, in the form illustrated, are altered in shape and size, but retain the beneficial

properties of the type disclosed herein in Figures 4-6 and 8. It will be appreciated that the

structure of Figure 11 may be used for diagnostic and monitoring functions as by recording

subdural EEG and may also be used therapeutically in stimulating the brain. The implanted

device 270 may contain amplifiers, modulators and internal data communication subsystem,

and a power source. The first antenna electrodes 276, 281, in the form shown, are integrated with the implanted device 270 at the ends thereof. These electrodes are

externally concave and may be covered with a gold foil to establish the two x-electrode

surfaces.

The implantable device 270 with the integrated first antenna electrodes 276, 281

preferably has a width of less than about 12 mm, a length of less than about 12 mm and a

thickness of less than about 4 mm.

As shown in Figure 12, the volume conduction first antenna 270, which has

electrodes 276, 281, is a directional antenna with the emitted current pulses, as exemplified

by lines 290, 292, being delivered generally in the direction of external second antenna

electrodes 300, 320, which are in contact with the scalp. The plastic sheet 272 is flexible,

thereby permitting it to be deformed freely to conform to the exterior shape of the cortex.

In the case where the recording/stimulation task will be performed within a sulcus, a

smaller flexible sheet with thinner contacts would be utilized to facilitate insertion into the

sulcus. A further alternative would be to use nanotube material to construct

stimulation/recording electrodes.

Among the advantages of the embodiment of Figures 11 and 12 are the use of a

relatively large surface area at each x-antenna electrode piece, thereby reducing the current

density in brain tissue surrounding the antenna electrodes and improving electrical contact

with the electrically conductive fluid within the brain. It also increases the efficiency of the

transmitter because of the larger separation, which may be on the order of 12 mm between

the two electrode surfaces. It further eliminates the need for a stand alone antenna

electrodes, thereby reducing the size of the implantable device and facilitating placement

during neurosurgery. Further, the flexible sheet 272 functions as a reflector which

strengthens the current field in direction of reception and weakens the current flowing from and into the brain. This latter feature is important, as it reduces the undesired brain

stimulation as the brain current shown in the dashed curve designated 330 is smaller than

the current in the direction of transmission.

While, for purposes of illustration herein, focus has been placed upon use of the

present invention in respect of brain, torso, and abdominal introduction of the implanted

device, it will be appreciated that a wide number of applications wherein an implantable

device can communicate information and receive information through the advantageous use

of volume conduction may be employed.

It will be appreciated that the present invention may be used for diagnostic and

monitoring functions, as well as for therapeutic activity. For example, obtaining

information regarding brain functioning, such as EEG and therapeutic use through

energizing the electrodes in deep-brain stimulation such as described in respect of Figures

11 and 12, may be beneficially provided. Further, examples of utility are in epileptic

seizure monitoring and intervention and bypassing brain signals to control limb movement

for people with spinal cord injuries.

It will be appreciated, therefore, that the present invention provides a unique method

and associated apparatus for efficiently having synchronized, two-way communication

between an internal device and an external device through current pulse conduction through

living biological tissues has been provided. The ionic fluid of biological tissue, such as

cerebrospinal fluid, for example, is highly electrically conductive. Certain preferred

features such as a highly efficient antenna which facilitates enhanced signal-to-noise ratio

and directional delivery and receipt of signals are provided. In addition, certain noise

reducing embodiments such as avoidance of the heart noise disturbances have also been

provided. Whereas particular embodiments of the invention have been described herein for

purposes of illustration, it will be evident to those skilled in the art that numerous variations

may be made without departing from the invention as set forth in the appended claims.

Claims

We Claim:

1. A method of data communication between an implanted device and an

external device comprising

providing an implanted device having a first antenna and first circuit components

operatively associated therewith,

providing an external device having a second antenna and an associated

microprocessor,

positioning said first antenna and said second antenna with living biological tissue

therebetween, and

effecting communication between said implanted device and said external device to

establish current pulses in at least one direction between said first antenna electrode and

said second antenna electrode.

2. The method of claim 1, including

implanting said implanted device in a living patient.

3. The method of claim 2, including

implanting said implanted device in a human being.

4. The method of claim 3, including

effecting said communication both from said first antenna to second antenna and

from said second antenna to said first antenna.

5. The method of claim 4, including

effecting said communication in a synchronous manner.

6. The method of claim 5, including

employing heart pulses of said human being as a clock in synchronizing said

communications.

7. The method of claim 4, including

providing a microprocessor as one of said first circuit components.

8. The method of claim 7, including

providing at least one sensor as one of said first circuit components.

9. The method of claim 8, including

implanting said implanted device in the brain of said human being.

10. The method of claim 4, including

implanting said implantable device in the abdomen of said human being.

11. The method of claim 9 , including

employing said method to monitor brain functioning.

12. The method of claim 10, including

employing said method to communicate subdural electroencepholographic signals to

said external device.

13. The method of claim 1, including

establishing the distance between said first antenna and said second antenna at less

than about 15 cm.

14. The method of claim 1, including

employing in said first antenna a pair of electrically conductive concave shells

having their concave surfaces facing in generally opposed directions from each other.

15. The method of claim 14, including

said electrically conductive concave shells having generally concave surfaces facing

each other, and

electrically insulating the convex surfaces of said electrically conductive shells of

said first antenna from each other.

16. The method of claim 4, including

placing the electrodes of said second antenna in contact with the skin of said human

being.

17. The method of claim 1, including

employing said method for diagnostic purposes.

18. The method of claim 1, including

employing said method for therapeutic purposes.

19. The method of claim 1, including

providing a power source as a said first circuit component in said implanted device.

20. The method of claim 1 , including

providing said first circuit components on an electronic chip.

21. The method of claim 20, including

providing said implanted first antenna on said electronic chip.

22. The method of claim 1, including

protectively encapsulating said implanted device with a resinous material.

23. The method of claim 1, including

directing the current pulses from said implanted first antenna through said biological

material to said external second antenna.

24. The method of claim 20, including

providing an electrically nonconductive flexible sheet to reflect brain current flux

and resist said fluid contacting said first antenna.

25. The method of claim 1 , including

employing said first antenna and said second antenna for both transmission and

reception of said current pulses.

26. The method of claim 1, including

said implantable device having a width of less than about 12 mm, a length of less

than about 12 mm and a thickness of less than about 4 mm.

27. The method of claim 8, including

employing said external device to transmit a current pulse to cause said internal

device to transmit data, said internal device responsively transmitting said data to said external device, and

said transmissions being effected at times other than the period of R-waves of an

electrocardiogram.

28. The method of claim 27 including said external device emitting a current pulse or pulses of the different sign or configuration from the pulses it emits when it requests data from said implanted device when it wishes to transmit data to said implanted device, and

said external device following said pulses with the desired transmitted data to said

implanted device with said pulses being transmitted at a time other than the time period when R-waves of the electrocardiogram are present.

29. The method of claim 21 , including

positioning said first antenna up to about 15 cm from said second antenna electrode.

30. The method of claim 14, including said shells being asymmetrical.

31. Apparatus for volume conduction between an implantable device and an

external device, comprising an implantable device having a first antenna and first circuit components for

transmitting current pulses through living biological tissue and receiving current pulses

therethrough,

a second antenna for transmitting current pulses through living biological tissue and

receiving current therethrough,

said first circuit components including a first microprocessor,

said external device having a second microprocessor,

said first antenna being a directional antenna, and

said apparatus being structured for directional data communication.

32. The apparatus of claim 31, including

employing in said first antenna electrodes having a pair of electrically conductive

concave shells facing in generally opposed directions from each other, and

said second antenna for contacting the skin generally adjacent said biological tissue.

33. The apparatus of claim 32, including

said antenna electrodes being asymmetrical.

34. The apparatus of claim 31, including

said first circuit components including at least one sensor.

35. The apparatus of claim 34, including

said implantable device structured to deliver EEG data to said external device.

36. The apparatus of claim 35, including

said antenna electrode shells having convex surfaces generally facing each other,

and

electrical insulation disposed on said convex surfaces.

37. The apparatus of claim 35, including said first circuit components including at least one power source.

38. The apparatus of claim 31, including

said implantable device being configured and dimensioned to be implantable in a

human abdomen.

39. The apparatus of claim 38, including

said implantable device having a width less than about 12 mm, a length less than

about 12, and a thickness less than about 4 mm.

40. The apparatus of claim 37, including

an electrically nonconductive flexible sheet for reflecting brain current flux away

from said first antenna disposed on the opposite side of said first antenna electrode from said second antenna.

41. An antenna for transmitting current through biological tissue comprising a pair of electrically conductive concave shells facing in opposed directions from

each other.

42. The apparatus of claim 41, including

said concave shells having convex surfaces generally facing each other, and

electrically insulative material disposed on said convex surfaces.

43. The apparatus of claim 42, including said antenna electrodes being asymmetrical.

44. The apparatus of claim 41, including said antennas having a maximum thickness of less than about 4 mm.

45. The apparatus of claim 43, including

said antenna having an upper portion that is longer than the lower portion measured along the electrode.

46. The apparatus of claim 41, including

said concave shells having a generally circular configuration as viewed in end

elevations.

47. The apparatus of claim 46, including said antenna electrodes being generally symmetrical.

48. The apparatus of claim 41, including

said concave shells having a generally rectangular configuration as viewed in end

elevation.