Implantable drug-dispensing capsule and system facilitating its use

The invention concerns an implantable drug-dispensing capsule and a process and system facilitating its use. According to the invention, a mechanism (7) for detecting the proximity of the injection needle (1) is provided inside the body (5) of the capsule (3), which detection mechanism is connected to an external signaling device (32) which signals when this proximity is realized. The invention is in particular applicable to the injection of various drugs in localized sites.

FIELD OF THE INVENTION 
The invention concerns a device facilitating the use of an implantable 
drug-dispensing capsule. 
BACKGROUND OF THE INVENTION 
In treating certain serious diseases, frequent injections of various drugs 
are required. Often these injections must be given venously or arterially, 
or by other means, so as to ensure local and precise distribution of the 
drugs used in treatment. In order to avoid inserting and withdrawing a 
catheter when each injection is administered, for many years now recourse 
has been had to implantable drug-dispensing capsules, placed under the 
patient's skin at a suitable point, and whose inner body communicates with 
a tube left in place in the body and emerging at the point where the 
injections are to be given. The capsule has a perforatable wall through 
which it is possible to inject the drug to be dispensed by means of a 
needle, the wall closing up again automatically when the needle is 
withdrawn. 
Generally speaking, and as it is understood in this field of application, a 
serious, fundamental problem presents itself with regard to the assurance 
that must be given to the practitioner that the needle is correctly 
introduced into the inner body of the dispensing capsule. Indeed, some of 
the drugs used may be of doubtful efficacy and cause the patient's death, 
or serious mishaps, if the drug injection, by mistake, is not made inside 
the body of the capsule and spreads, for example, between the capsule and 
the skin covering it. 
In some systems for registering the proper introduction of the needle of 
the injection syringe into the body of the drug-dispensing capsule, this 
same capsule is placed in contact by its outer wall with the patient's 
body and has an electrically conducting inner wall forming a detection 
device near the end of this needle. In addition, it is known that the 
registering system can be equipped with an external signaling apparatus, 
connected to the aforementioned detection device, which responds to the 
closing through the patient's body of an electrical circuit that includes 
the inner conducting wall of the aforementioned capsule and the needle. 
Such systems nonetheless present a certain number of drawbacks. 
Indeed, it has been recognized that, together with the fundamental problem 
regarding assurance of proper introduction of the needle, practical 
difficulties were posed for the application and utilization of the known 
systems. More precisely, it was noted that the signaling device that 
alerts the practitioner to the correct introduction of the needle was 
sometimes prematurely triggered while the needle was still not in contact 
with the bottom of the capsule. A slight variation in impedance, too 
rapid, could trip the device, understandably posing a real danger to the 
patient. 
BRIEF DESCRIPTION OF THE PRESENT INVENTION 
The invention is particularly intended to solve this difficulty, together 
with the fundamental problem mentioned previously, by enabling the 
practitioner to determine with certainty the moment when the injection 
needle is actually and correctly introduced up to the inner conducting 
wall inside the body of the capsule, without the risk of premature, too 
rapid tripping of the signaling device informing him that he may inject 
the drug. 
This purpose is achieved according to the invention by providing that the 
electrical circuit of the aforementioned registering system includes, in 
addition to the capsule's inner conducting wall and the needle, 
an AC generator, the lead-in of which is connected to the positive pole of 
a DC voltage source, 
an assembly of the rectifier/filter type, said assembly being connected: 
by a first input terminal, to the outlet of the aforesaid AC generator, 
by a second terminal, to the negative pole of said DC source, 
at least one comparator connected 
by lead-out, to said signaling device, 
by lead-in, to a third output terminal of the rectifier/filter assembly and 
to a comparison unit intended to provide a reference voltage, said 
comparator being subjected to the difference in voltage between that 
delivered by said rectifier/filter assembly and that delivered by said 
comparison unit, and being fed, along with said signaling device, by said 
DC source, 
a surface electrode placed on the patient's skin, said electrode being 
connected in the circuit's closed state in series with said needle, the 
patient's body, and/or said inner wall of the capsule towards the input 
terminal of said rectifier/filter assembly. 
According to a preferred characteristic, the aforementioned comparison unit 
includes: 
a sequencing clock, one input terminal of which is connected to the output 
terminal of the rectifier/filter assembly, 
two switches placed on the clock's control, 
a condenser or similar device that discharges towards an input of the 
comparator in a closed position of one of the switches, and 
a voltage-dividing bridge charging the condenser in the closed position of 
the other switch, the two switches working in anti-parallel phases. 
In this way, the system is prevented from taking into account small 
variations in impedance, the magnitude of which is basically a function of 
the speed at which the injection needle is introduced. 
In other words, this invention ensures that the signaling device is tripped 
only when the impedance drops suddenly and relatively significantly, i.e., 
basically only upon contact between the end of the injection needle and 
the inner conducting wall of the capsule. 
It will likewise be noted that the invention, by providing an AC generator, 
makes it possible to solve a delicate problem regarding the overall 
effectiveness of the system. Indeed, by the capsule being placed under the 
skin and being utilized, fibrous tissues are created around the capsule 
which hinder the passage of electrical energy, especially that which would 
be delivered by a DC generator or source. Operation on AC solves this 
additional difficulty. 
In addition, such a current generator is entirely suitable in that it makes 
it possible to control the electrical energy passing through the patient's 
body by checking only one variable: the current. 
The invention and its implementation will appear more clearly with the aid 
of the following description, given in reference to the attached drawings 
illustrating methods of implementation. In these drawings:

DETAILED DESCRIPTION OF THE INVENTION 
It will immediately be noted that, in FIGS. 1 and 2, the circuit's linkage 
or nodal points have been marked by a dark dot in order to facilitate 
reading the drawings. 
Referring first to FIG. 1, the needle 1 has been shown with its head 2 for 
adapting it to any appropriate injection and/or puncture system (not 
shown). Opposite is shown a capsule 3 implantable under a patient's skin 
4, this capsule including a self-sealing wall 6, enclosing its inner body 
5, of a type that is known, especially in silicone-coated plastic. The 
bottom inner wall 7 of the capsule is metal, whereas the rest of the 
capsule, and particularly the side wall 8, is of an electrical insulating 
material, such as a plastic of a suitable quality. The capsule's body 5 
communicates with a tube 8' through which are injected the drugs to be 
introduced, and through which drawoffs for analyses or punctures can also 
be made. The invention's system also includes a DC source 9 of a suitable 
quality (voltage/density). According to the invention, the input 11a of an 
AC generator 11 is connected to the positive pole of the DC source 9 
through a feed line 10. The output 11b of this same generator 11 is 
connected to an input terminal 12a of an assembly 12 forming a 
rectifier/filter. 
The assembly 12 includes, as illustrated, a diode 33, or similar device, 
forming a rectifier connected between the input 12a and the output 12c, a 
condenser 34 connected on one side to the unit's feed line, towards the 
diode's cathode, and on the other, leading out from the terminal 12b, to 
the negative pole of the source 9, through the circuit's ground line 13. 
Parallel to the condenser's terminals is mounted a relatively strong 
resistor 35. 
The diode is mounted passing towards the assembly's output 12c. 
At 17, the double arrow indicates the reduced-resistance electrical path 
existing through the patient's body between a surface electrode 16 
connected at 14a by a conductor 14 to the ground line 13 and the 
relatively broad-surfaced metal wall 7 of the capsule 3. A conductor 15 
also makes it possible to connect at 15a the head 2 of the needle 1 
between the output 11b of the AC generator 11 and the input terminal 12a 
of the assembly 12. Thus, when the needle 1 comes into contact with at 
least the patient's skin 4, the circuit is closed in series over the 
needle, the surface electrode, and the patient's body. 
Connected to the output terminal 12c of the aforementioned rectifier/filter 
unit 12 are, at the site of a node 18, the positive input 19a of a 
comparator 19, itself connected to the signaling device 32, and a 
comparison unit 50 intended to supply to the negative input 19b of this 
same comparator a variable voltage, as will be seen subsequently. The unit 
50 includes a clock 20, a voltage divider 22, a condenser 25, and two 
switches 23a, 23b. The input terminal of the sequencing clock 20 is 
connected to the node 18, while one of the poles of the voltage divider 22 
is connected at 21, also to the terminal 12c of the assembly 12. The other 
pole of this same divider is linked with the ground line 13. 
The two switches 23a, 23b are placed under the dependency of the clock 20. 
They are connected on the one hand to one another by means of a conductor 
27, and, on the other, at the site of their respective remaining terminal, 
for the assembly 23a, to the lead-out line of the switch 12, at 21, and, 
for the switch 23b, to the negative input 19b of the comparator 19. 
Connected at 26 to the conductor 27 of one terminal of each of the two 
switches is one pole of the condenser 25, the other pole of which is 
connected to the ground line 13. 
In the case envisaged, the switches are of the "all or nothing" type, open 
or closed. In the figures, they have both been represented in the open 
position, even though they are intended to operate in anti-parallel phase. 
The drive or control action of the clock 20 on the two switches 23a, 23b is 
achieved through two conductors respectively 20a, 20b connected to two 
output terminals of the clock 20. 
With regard to the signaling device 32, it will be noted, as illustrated, 
that the output 19c of the comparator 19 is parallel-connected both to a 
device 28 for shaping a sound signal that will be able to activate a sound 
device 29 and to a device 30 for shaping the signal that will be able to 
activate a signal light 31. 
In order to ensure operation of the circuit just described, the DC source 
9, which may in particular be a simple galvanic cell, shunt-feeds, through 
the feed line 10 and the ground line 13, the two signal-shaping devices 
28, 30, the comparator 19, the unit 24 including the two switches 23a, 
23b, and the sequencing clock 20. 
The operation of the invention's system, the assembly circuit of which has 
just been described, can be clearly deduced from the foregoing. 
In the state illustrated in the figure, where the needle 1 is drawn back 
from the metal conducting wall 7 of the capsule 3, the electrical circuit 
through the needle and the capsule is open, there being a virtually 
infinite resistance between its terminals. 
When the needle 1 is pushed through the patient's skin 4, resistance 
decreases, the electrical circuit being closed through the patient's body 
and skin. However, this resistance is still very strong because of the 
limited, pinpoint contact between the needle 1 and the skin 4 at the site 
where this same needle is passing through the skin. By way of example, it 
will be noted that this resistance may be on the order of 30,000 ohms. 
Finally, when the needle has perforated the wall 6 and comes in contact 
with the metal wall 7 of the capsule, the resistance decreases 
considerably, not exceeding 1,000 ohms, for example. At the site of the 
comparator 19, it is this variation in impedance which is exploited by the 
comparator to trip the signals. 
Of course, the system is time-delayed so that the sound signal and the 
light signal last long enough to eliminate any doubt from the user's mind 
that the signal is present. 
In fact, the comparator will only trigger the signals if the voltage 
reaching its positive terminal 19a is lower than a previously memorized 
voltage reaching its negative terminal 19b. 
Indeed, once the circuit is closed and the source 9 receives voltage, the 
clock is triggered and alternately controls the switch 23a or the switch 
23b at each surge. At the same time, the AC generator 11 feeds the 
assembly 12 (diode 33, condenser 34, resistor 35) which receives, at 12a, 
an alternating current, rectifies it, filters it, or integrates it, and 
puts out between its terminals 12c, 12b a direct current U as a function 
of the current passing through the resistance of the patient's body and/or 
in the capsule. The voltage U occurs again at the terminals of the voltage 
divider 22 and at the positive input 19a of the comparator 19. 
Let .rho. be the surge phase of the clock which, upon closing, controls the 
switch 23a, and .rho. the phase which, also upon closing, controls the 
switch 23b. It will be recalled that the two switches work, preferably, in 
anti-parallel phases. 
In phase .rho., the switch 23a is closed, while 23b is open. The condenser 
25 is charged by the voltage delivered by the voltage divider 22, i.e., by 
a fraction of the voltage U, or U/X with X: the ratio of the voltage 
divider. 
In phase .rho., the switch 23b is closed, while 23a is open. The condenser 
25 then discharges towards the negative input 19b of the comparator 19, 
which then compares the value of a voltage U' which has just been received 
at its positive terminal 19a to the memorized voltage value U/X received 
at its negative terminal 19b. In other words, the comparator 19 makes a 
comparison between a voltage proportional to the current that has just 
passed through the patient's body and a previous fractional value of that 
voltage which was stored in the condenser. 
In particular, it is possible to see that the voltage divider 22 is set 
with X=4. The voltage delivered will then be U/4, with a voltage U at the 
input. 
The comparator 19 will then trigger the signals if it receives a voltage U' 
lower than U/4, i.e., if there is a significant collapse in impedance 
indicating contact between the needle 1 and wall 7 of the capsule, and 
hence a correct introduction of the needle. 
The clock 20 can be set at about 100 times the speed v of the needle's 
penetration into the site. It is possible to take v on the order of 100 
ms, and, hence, .rho.(or .rho.) equal to about 1 ms. The needle's speed of 
introduction is thus prevented from interfering with the operation of the 
system and causing a premature tripping of the signals. 
Reference will now be had to FIG. 2, in order to see illustrated a 
preferred and somewhat more complete mode of realization of the electrical 
assembly represented in FIG. 1. 
The circuit in FIG. 2 includes all components presented in reference to 
FIG. 1 and which have consequently been assigned the same numbers and will 
not be described again. 
In particular, in addition to the needle, also present once again are the 
capsule 3 and the surface electrode 16, the AC generator 11, the 
rectifier/filter assembly 12, the clock 20, the voltage divider 22, the 
switches 23a and 23b, the comparator 19 and the signaling device 32, as 
well as the DC source 9. 
A second comparator 36 and two voltage followers respectively 37 and 38 
have been added to the assembly. 
In addition, the signal-shaping devices 28, 30 have been illustrated in 
greater detail. 
More specifically, the second comparator 36 has been placed between the 
node 18 and the input terminal of the clock 20. More precisely, its 
positive input pole 36a is linked to the output terminal 12c of the 
rectifier/filter assembly 12, while its negative input pole 36b is 
connected to a comparison or reference unit 39, known in itself, 
delivering a fixed voltage. 
The comparator 36 is set so that it controls the triggering of the clock 20 
when the voltage applied to its pole 36a falls below a determined 
threshold selected in relation to the voltage prevailing at its pole 36b 
which receives the reference voltage. In practice, the comparator will 
preferably be set to be triggered upon contact of the needle 1 with the 
patient's skin 4. It improves the system's reliability. 
As for the voltage followers 37 and 38, they are respectively mounted on 
the feed line 40 of the positive terminal of the comparator 19 and on that 
41 of the voltage divider 22, so that their respective inputs are 
subjected to the voltage U (or U') delivered by the rectifier/filter 
assembly 12. 
With regard to the shaping devices 28, 30, each includes a monostable 
circuit 42, 44 controlled by the comparator 19 and, in series, an 
adaptation circuit 43, 45. 
Of course, the comparator 36, the two followers 37, 38 and the components 
of the devices 28, 30 are shunt-fed by the DC source 9. 
In terms of practical utilization, it will be noted that the model LD 161 
manufactured by INTERSIL can be used as comparator 36. This same model 
would also be suitable for the comparator 19. 
The two voltage followers 37, 38 could be of the TL081 type manufactured by 
TEXAS INSTRUMENTS. 
In terms of selection of components, one could choose a condenser 25 of 
about 100 nF, a condenser 34 of about 10 nF, a resistor 35 basically equal 
to 2M.OMEGA., an AC generator 11 delivering about about 100 .mu.A with a 
current source 9 of about .+-.9V. 
FIG. 3 will now be discussed; it illustrates the realization of a capsule 
specially adapted for the use described above. 
The capsule basically includes a pressed-metal wall 7, of stainless steel 
or titanium, for example. The metal bottom has the shape shown in FIG. 3 
of a basin, the inner body 5 of the capsule being enclosed by the 
self-sealing perforatable wall 6 placed on the basin. The wall 6 can be 
held in place by a metal washer 46 soldered as indicated at 47 towards the 
outer edge of the basin-shaped wall 7. The whole is then covered by a 
molded plastic material 48 electrically insulating the whole of the 
capsule from the patient's body, except for the bottom-center wall 7a of 
the capsule which will come in contact with the patient's body, a bone, 
for example, onto which the capsule will be fixed. Finally, the inner body 
5 of the capsule communicates through a metal tube 8', appropriately 
soldered or crimped, passing through the wall 7, the assembly being 
suitably protected by the molded plastic 48. It will be noted that, with 
such a capsule, when the wall 6 is perforated by the injection needle, 
there is no risk of obtaining a false contact signal if the needle is 
poorly guided and runs into the insulating wall of the capsule's covering 
48. 
Several variants can be introduced in the modes of realization described, 
both in the constitution of the capsule and in the generation of the 
signal indicating correct and complete introduction of the needle into the 
body of the capsule as far as its inner metal bottom. For example, in the 
case of the assembly illustrated in FIG. 1, one might consider using, 
instead of the comparator 19 and the comparison unit 50, the 
aforementioned comparator 36 with its comparison unit 39. 
In this case, the signaling device 32 would be connected directly to the 
output of the comparator 36. The remainder of the circuit would be 
identical to the one illustrated. 
With such an assembly, and as it is understood, the variation in impedance 
associated with the needle's penetration towards the capsule's conducting 
bottom would be exploited by the comparator 36 to trigger at a determined 
threshold, for example 2,000 ohms, the signals indicating proper 
introduction. However, in this case there would of course be no comparison 
between an immediate voltage and a previous value that would have been 
stored for a short time. In other words, and in practice, such a system, 
though quite usable, would not make it possible to be free from the 
uncertainties of premature triggering of the signaling device associated 
with the needle's speed of penetration.