Note: Descriptions are shown in the official language in which they were submitted.
79~86
11 .
BACKGROUND OF T~IE INVENTION
The invention relates to the precision measuring and
monitoring of pressures in the living body, such as intracranial
pressure in the head, by means of a long-term,totally implanted
~i sensor which undergoes a conformational change with pressure and
i,which is coupled through the skin by electromagnetic, acoustic, or¦
mechanical transmission to an external device which detects that
¦Ichange and interprets the pressure. The invention refers
additionally to a device which is automatically barometric
' compensated, has immediate zero point reference check, can be made
I passive, and is insensitive to barometric or temperature changes.
Ij At the present time there is no such wireless device
I!available for general clinical or research purposes. ~he uses fo
jlsuch a device in neurosurgery would be immediate in the management
of intracranial hypertension, monitoring of intracranial pressure I
¦,in all cases of intracranial neurosurgery and head trauma, long- ¦
~term diagnostics for evidence of tumor recurrence, and management
jof hydrocephalus.
All devices previously proposed have significant short-
!~ comings which make them impractical for widespread, safe,
jlaccurate, reliable, and long-term use as intracranial pressure
¦jmonitors. Most designs involve a tube or wire connection through
the skin to an external device, and since this greatly increases
" jj , 1.
' 1' .2.
1-
,
: ' ~ ' ' -
`
1 ~079086
' the chance of infection and electrical shock to the patient and
reduces the patient's mobility they are hazardous and impractical.
Of the devices which are wireless and fully implanted, they
usually involve a sealed inner volume containing a fixed amount of
,. I
5 ~ gas, this being housed in a flexible container which deflects
under pressure. The major problems with this design aspect are
the following: liquids and gases will inevitably diffuse through
the membranes and walls of the container causing steady drift of
the zero-point reading, and causing an unpredictable error in the
0 !I device's ca~ibration; changes in barometric pressure wili cause
significant variations in the body pressure relative to the fixed
- volume pressure and thus the device' 5 pressure readout must be
! corrected for barometric pressure changes in the external detection
i system; a trapped volume of significant size could make it
dangerous for a patient to experience atmospheric pressure change,
such as those found in air travel, for fear of rupturing the
device; and temperature changes in the patient will cause changes j
in the trapped volume and resultant errors in the pressure reading.
I Previous totally implanted designs provide no means to check out
their zero-pressure calibration after implantation and thus no
means to determine diffusion or temperature drifts in the readings
nor 21ny check of the proper function of the device, which is
'essential for long and short-term implantation. Most previous
i designs are of complex construction, involve high tolerance parts
,1
..
I, , i
,
! 11 ` 1
i
i: . 3.
-~ ! .
,
' ' " : ': - ` ~ ,
:' ' ', ~ ` ' ' `: ~ : ' `-
.
.
~ . . .
': . , :
- ' 10790~6
. , .
~' I
and assembly, and are not amenable to calibration standardization;
all of which make them expensive, inaccurate, and unsuitable for
' simple and general application.
ij Accordingly, some of the principal objects of the present
5. Ilinvention are the following: . !
, ' ~1) To provide a pressure detector which can be implanted
for an indefinite period under a fully intact skin with no ~ire or
j,tube connections to the exterior so as to reduce infection and
electrical shock hazard, and to read pressures in inaccessible
o !~ spaces ln the body, such as intracranial pressure, with an
' accuracy of 5 to 10% or better.
(2) To eliminate or make insignificant all inaccuracies, ll
and dependencies on a trapped volume of gas or fluid in the device,
~to make the pressure readings insensltive to drifts from membrane
~ permeability, barometric change, and temperature variation, and
,` to eliminate the hazard of rupturing the device during air travel.
(3) To provide automatic barometric compensation as a
built-in feature of the implanted device.
¦~ (4) To provide a means of easily and instantly checking
I,the zero-pressure calibration of the device.
¦l (5) To provide a sufficiently fast dynamic response to
enable observation of variations in the body pressure due to heart
rate, respiration, and any other physiological changes.
1~1 - .
:' '
' !! ; 4~ I
.~ ' ' , ' ' .
' ' ' '
.. r~ j
1079086
i' . i
~6) To allow a simple calibration standardization of the
; implant.
(7) To allow the implanted device to be of simple, I
Ilpassive, compact, and low cost construction so as to be implanted ¦
¦~permanently and to function properly for indefinitely long periods.
(8) To make the system amenable to telemetry over long
~distances so as to monitor pressures in a freely moving patient.
'
.
' . , ' I -,
!
;; ' ' . I
!. I:
,1 . I .
1. . 1
:, , :
_........ ~. ... ~
: ' ' - . . , ' ' :
. "' ' . . ' ': ' ' '. '~
" ' ' ' : . '' '
-- ' .. . . : . ,: . ,. '. '-: ' '
f
~' I
- 1079~)86 ~ ~
~.
. SUMMARY OF THE INVENTION
.
i
The above objects and advantages are achieved by the
¦ present invention as described in the following brief summary:
'The implanted pressure sensor comprises an insulating body with a
,Imovable element that moves through an opening or channel in~the
5 i,body. The movable element communicates with external atmospheric ¦
¦Ipressure on one side by means of a membrane which is nearly
coplanar with the intact skin covering it, and with the internal
pressure on the other side, also by a membrane, so that the degreej
Ilof the movable element'sdisplacement relative to the body is
,,directly related to the difference in the internal and atmospheric
jlpressures. Thus,since the pressure-dependent distortion of the
implanted sensor does not involve variation of the volume of a
i'trapped gas or space all problems related to the latter are
eliminated. Also, since direct sensing of atmospheric pressure
is 11 is exploited, barometric compensation is built-in and automatic.
Further, the skin may be pressed manually just above the implantedl
I device, and the movable element can be thus pushed back to a stop ¦
- ~'point in the device's body corresponding to equilibirium; thereby ¦
I~allowing the zero-point pressure position to be checked instantly
~¦at any time. The implanted device is coupled to an external
¦idetection system by electromagnetic, acoustic, or other radiation
11
' I '
~. ~ 6- .
I
. . , ' ' .
,,` . ` -, ' ' ~ , '
. .
,,
1079(~86
or transmission means across the intact intervening skin. The
external de~ector system can determine the position of the
movable element's displacement and thus the difference between
the internal and atmospheric pressures. A variety of means of
interrogating the implant by the external device are possible,
but a particularly simple method involving a passive implant
consists of building a fixed and parallel coil and capacitor
combination into the body of the implant and a magnetic material
into the movable element which moves through the coil, thus
varying its inductance with varying displacement or internal
pressure. The internal L-C resonant circuit is coupled electro-
magnetically to an external swept oscillator pickup circuit
which detects the resonant frequency of the L-C circuit and
related it to the coils plus magnetic material's inductance
and corresponding internal pressure. As will be shown below,
this construction is simple, compact, economical, free of
thermal, diffusion, or mechanical drlfts, calibration standardized,
fast responding, adaptable to remote telemetry, and incorporable
in a large number of multiple function implant configurations.
Specifically, the invention relates to a differential
pressure sensor comprising: a housing having means defining
an opening, extending therethrough; a first flexible diaphragm
extending across the housing opening and being fluid pressure
sealed with respect to the housing; a second flexible diaphragm
, extending across the housing opening and being fluid pressure
,` sealed with respect to the housing, the diaphragms and opening
defining means forming a closed volume with the first diaphragm
communicating with the pressure in one region adjacent to the
6ensor and the æecond diaphragm communicating with the pressure
.
mb~ T- 7 ~
. . . ~ .
1079086
in another region adjacent to the sensor; means for motion
coupling the first and second diaphragms; means for defining
a reference position of at least one of the diaphragms or of
the motion coupling means with respect to the housing; and,
means having a preselected, detectable variable parameter
that is a known function of the displacement of at least one
of the diaphragms or of the motion coupling means from the
reference position, the displacement being a known function
of the difference in the external pressures on the diaphragms.
In its method aspect, the invention relates to a
method for remotely detecting in vivo pressure, the method
comprising the steps of: implanting in a living body a
differential pressure sensor comprising: a housing having
means difining an opening extending therethrough; flexible
diaphragm means extending across the housing opening and being
fluid pressure sealed with respect to the housing; the
diaphragm means communicating with pressures in two separate
regions external to the sensor that are separated by the
flexible diaphragm means with the pressure in one of the regions
being an internal bodily pressure when the sensor is implanted
in a living body; means for defining a reference position of
the diaphragm with respect to the housing; and, means having
a preselected, detectable variable parameter that is a known
function of the displacement of the diaphragm means from the
; reference position, the displacement being a known function
of the differences in the external pressures on the diaphragm
means. The method then includes the further steps of calibrating
the implanted sensor by:
' .
mb/~ 7a -
': . :
. ' ,. : :
.: . - , .
'~ , :
. .
.
1079~86
(1) manipulating the sensor through the intact
skin of the body to cause the sensor to assume the reference
position; remotely detecting the value of the variable
parameter when the sensor is in the reference position;
terminating the manipulation of the sensor; and therefore
remotely detecting any change in the value of the variable
parameter from the value at the reference position without
any connection to the sensor which requires a break in the
skin, the change in value representing the difference in
pressure on the sensor diaphragm means.
A fuller understanding of the invention and
additional objects, advantages, and novel aspects of it will
be gained from the following detailed description, illustrative
drawings, and various embodiments and implementations. There
are many design variations on the present invention concept
which are possible,
.
mb/~ 7b -
. '- . - .' ' . ' . ~ ' ' : '
~, . . -
. . .~, . .
. ~ 1079086 -` ~
Isuch as, constructional details, choice of specific conformations,
¦various methods of coupling and information transfer from implant
¦to external detector, and variations on the electronic design
¦within the state of current electrical engineering art of both
¦implanted and external circuitry. Such variations which are
¦included within the scope of the claims below are understood to
¦ be included in the present invention disclosure. Furthermore,
I although the present inventive concept may be adapted to pressure
¦ measurement in numerous locations in the human body, it is highly
¦ illustrative to show its application as an intracranial pressure
¦ monitor. It is understood that the scope of the invention covers
¦ the use in areas of the body other than just the head.
., I : .
I .
~ . . ~ . _
- ' ' , '
,
-: : : . ' . '' , : ' ,
~ ' ' , ' . ,
,
:
!l
1~79086
., !
DESCRIPTION OF THE DR~WINGS
! .
I In the following drawings similar reference characters
¦ represent similar parts.
,¦ Figure 1 shows a schematic, vertical sectional view of
I an implanted sensor being used to measure intracranial pressure in
1 a living human being.
- ¦ Figure 2 shows a view in vertical section of a more
¦ specific design of the invention concept of Figure 1 for ï~tracranlal
pressure measurement.
Figure 3 illustrates the arrangement of the sensor such
as that in Figure 1 relative to the external "grid-dip" type
oscillator with pickup antenna and the other associated circuitry -
for signal analysis and digital or chart recorder readout of the
¦ intracranial pressure.
~ ¦ Figure 4 shows another variant of the design of Figure
- l 2 in which a capacitive type electronic coupling through the skin ¦
¦ i8 used to determine the resonant frequency of the internal L-C
¦circuit. '
¦ Figure 5 is a schematic circuit and block diagram
¦illustrating the method used in Figure 4.
¦ Figure 6 illustrates schematically another means of
coupling through the skin. -
~1 Fig=re 7 lll=ctr tes ye~ another meqnc oi ~oupling
; . ' . :
~ ' ' '~' " ' ' ' ' ' :
~1 107908
. .
. ` .
through the skin.
Figure 8 is yet another coupling scheme.
Figure 9 shows a view in vertical section of another more
compact variation of the concepts of Figures 1 and 2 utilizing a
, single membrane and being incorporated in a system for measuring
intraventricular pressure.
Figure 10 shows a design similar to that in Figure 9 but
working in conjunction with a cerebrospinal fluid shunt valve.
Figure 11 illustrates differential sensor of pressures
in two different regions.
Figure 12 illustrates a differential pressure sensor in
combination with a fluid shunt valve and a fluid regulator;
Figure 13 illustrates a pressure sensor in which pressure
is communicated to an upper diaphragm through a closed fluid
system.
Figure 14 illustrates another configuration similar to
that shown in Figure 10, except that the differential pressure
sensor functions only as a pressure measuring device and not as a
variable valve.
Referring to Figure 1, the major elements of the
implanted pressure sensor, used in this example as a monitor of
epidermal intracranial pressure if the dural membrane 1 is intact
or of cerebrospina1 flui pr-ssure th~t surrou=ds th - bra~n 3 i
~ 11
'~' 11 ~0
10'790~
I . '
I' . .
the dura 1 is cut, may be understood as follows: The sensor,
¦which is inserted in a burr hole drilled in the skull 4 comprises
a housing 5 having a through opening in which travels a movable
¦ element 6. An inner flexible diaphragm 7 attached to housing 5
5'¦ communicates the intracranial pressure~ICP~ to one side of
¦ movable element 6 while an outer diaphragm 7' communicates the
. ¦ pressure of the atmosphere 8, P(ATM) which is transmitted across
. ¦ the intact scalp 9, to the other side of 6. By this system a
difference in ~(ICP)- P (ATM)will cause a force imbalance on the
in~er diaphr-gm ~ ~A- -y ro~_~ spr~ g 1--d~ g ~he ~vable
~,
A.
. . ~ - _
,
'" ' , :
10790
element 6 relative to the housing 5 a calibrated relationship of
the displacement of the movable element relative to the housing
can be achieved.
This displacement will cause calibrated physical or
, electrical changes in some characteristic parameters within the
sensor, and these changes are detected by an external detection
system 10 which is coupled to the sensor by electromagnetic,
acoustic, or other means across the skin, but not through the
skin as by a tube or wire. The detector 10 thus interpretes the
displacement and reads out the associated barometrically
. compensated intracranial pressure~(ICP)-p(AT~ A mechanical stop,
fiducial, or shoulder 11 is employed to interrupt the downward
movement of the movable element relative to the housing so that
by pressing on the skin just above diaphragm 7' an instant check
of the zero-point of~lICP)-~(AT~1)can be made.
Referring to Figure 2, a specific and practical design
involving the basic inventive concepts of Figure 1 is shown. The
cylindrical hous ng 5 is formed of an insulating plastic, such as,
nylon or "Lexan", and has an upper flange so that it seats in a
; 20 standard burr hole in the skull 4. A fixed coil 12 and capacitor
- 13 are imbedded in the housing to form a parallel L-C tank circuit .
A slug 14 of magnetic material moves in a cylindrical hole throug
. the hou-ing S aDd is ~ct ed to 4 w-xi-l cylln~rical cecl~er 15,
: .''.' . , , ',, , ,'. '
. . . ' '.' ' , . . :
~, . ' . , , ' ' ,
:'; .. . , ' ". ' 11. '' .
:. . . I ~ ' _. _
: . ' : ; . '
' ' ' , : ~ :
. '- : ' ' ~
- ' ' , ~ . ' ' .
10790 6
¦made of a plastic material, to form the movable element 6 of
Figure 1. The two diaphragms 7 and 7' are made of thin plastic
¦ material, preferably convoluted for flexibility, and hermetically
¦ attached to housing 5. The diaphragms contact the ends of slug 14
¦ and cylindrical member 15, respectively. The two diaphragms 7 and
¦ 7' in combination with the slug 14 and member 15 form a duaI
1 motion-coupled diaphragm system with end-for-end symmetry such .
.. . I that ~(ICP)is felt on one end,~(ATM)is communicated through the .:
¦ intact skin and is felt on the other end, and the e~ternal force
¦ on the slug 14 and member 15 is directly proportional to the
¦ difference ~ = ~ICP) -~(AT~ .
. ¦ When ~(ICP)is greater than~(ATM~ the magnetic slug 14 .
¦ will move upward relative to coil 12 thus changing the inductance
l of the coil-magnetic slug system This in turn will cause a change
- 15 ¦ in the resonant frequency of the L-C tank circuit, which is
. ¦ detected outside the body by an external detector system 10
: ¦ described below. The magnetic slug 14.moves against a spring 16
so that the amount of its displacement X is proportional to the
. ¦ pressure imbalance ~ ; i.e. ~ -p(ICP)-~(ATM)= kx, where k is
¦ the spring constant. Thus the change in resonant frequency of
¦ the L-C circuit can be directly related to ~ . .
. ¦ Detection of the sensor's L-C resonant frequency, and
thus the Jt=os~h-rically c mpensated intracranial pressure
~ I ~
'' ''.
: , . ' : ' ' ~ ' : .'
~ ' ; ' . ' ~ : : '
¦can be easily accomplished by coupling the sensor's L-C circuit
electromagnetically to the external antenna-oscillator system 10
which can detect a power dip at the resonant L-C frequency. Such
. ¦ detector circuits have been well known in radio engineering for
,¦ decades as "grid-dip" oscillators and now can be made very .
compactly with integrated circuits. Such dip oscillators operate
L : A ~ ~
:. : . . , . . .... :
.
1! 1079086
typically at 10 to 100 Me~a ~ertz ~d are swe~ o~er the resona=t
!jfrequency at audio rates. The resonant power dip signal is
¦Idetected by common peak detection methods. Figure 3 illustrates
¦!a typical arrangement of patient 17, sensor 18, and external
Idetection system. The external pickup antenna lg can be coupled
- l'satisfactorily at several inches from the patient's head and forms¦
the inductance of the swept oscillator contained in box 20. The
frequency dip signal of the oscillator is analyzed in console 21
Iland displayed by analog or digital meters or by chart recorder.
1I Several ancillary points and advantages of the design in
¦Figure 2 enable the aforestated objects of the invention to be
achieved. The end-for-end symmetry of the dual motion-coupled
diaphragm system, plus the convoluted flexible diaphragms, plus
llthe very small innerspace V(IN)which is required only for wall
¦clearance of the spring and the cylindes 14 and 15 not only make
¦jautomatic barometric compensation possible, but also eliminate
drift due to diaphragm permeability, aberrations due to barometric
pressure change, and hazard of rupture during air travel. If the
¦innerspace volume V(IN)iS initially filled with air and if
,diffusion of this ga5 outward and of fluid inward after implantatic n
cau8e a reduced pressure ~(IN) in ~IN~, then because of end-for-end
symmetry of 7, 7', 14, and 15 the forces on diaphragms 7 and 7'
i will be the same function of P(ICP~ - P(IN)and ~ TM)-P(IN), and thus
¦ tho ne~ foro-~ nd ssocl ed d--pl-c _ =t, of ylinde l4 ~-d 15
.,' ' ",,. .' "' ''.,'', ' . .
1~ l
~ _ . ~ ,. , , _
~"~ . .
,
.
' '
. ' ' : . . :.:
. ' - ' , .
10790~
will depend only on ~P = P(ICP) -p~T~I)and not on P(IN~ Should
sudden change of ~P ~ATr~)in barometric pressure, p(ATIi~ occur as
.. n air flight the change in ~(IN)will be roughly
(IN) _ - p ~ ) V (IN)
nd if ~ (IN)is very small, so will be ~ (IN~. Thus, the
.. erturbation on and danger of rupturing of diaphragms 7 and 7' will
e accordingly small, and again end-for-end symmetry will cancel
l ny effect on the measurement of ~p . The same argument applies
o changes in P(IN)or V (INJbecause of changes in surrounding .
. l emperature.. . -
. The novel features of the external communication of the
sensor through the skin and the provision of a shoulder stop 11
for elements 14 and 15 against the housing 5 at equilibrium .
~ . position, not only allow an instant zero pressure reference check,
: but also insures an instant check of the operation of the entire
. system and correction to any temperature dependent variations in
. the electro-mechanical characteristics of the sensor. The coil 12
and capacitor 13 can easily be selected for negligible temperature
. drift and high resonant Q. The cylindrical elements 14 and 15 can
. . . be teflon coated and axially suspended on diaphragms 7 and 7' so
. that friction is minimized and the static and dynamic response and
8ensitivity are maximized. .
~he de~iy- hao be decons~ra e~ in
,: . . ' ' - ~ .
: _ . . 14- _
_~ .
... . ~- . . I
. ~ . - .- . - -
.. . . . . .. :
. . . . .
, ~ . .
... .. . ~ - .
;
', 107908~;
Il . .
implantations to detect differences in intracranial pressure of
I less than 5 mm of H20 and to record easily the rapid pressure
¦~ variations due to heart beat and respiration, these being
¦1 important clinical indications of a working system which previousl
!¦ designs cannot achieve. The diaphragms 7 and 7' may be arranged ¦
,Ij coplanar with the dura 1 and scalp 9, respectively, during
Il equilibrium so that surface tension effects of the latter a~e
¦¦ minimized and fibrosis of the dura will not occur in long
¦¦ implantations, a problem which has plagued previous designs. The
ll sensor is cosmetically inobtrusive, lying flat with the scull 4,
and a full range of clinically important pressures from 0-100 cm
¦l of water may be read with only 1/2 mm total displacement of
¦ cylinder 14 and 15, The design of Figure 2 can be made less than
¦ 1/2 inch in diameter and as shallow as 3 to 11 mm total height,
15 . ! making them adaptable to infants or small animals as well as
j adults. The design is easily calibration standardized by
ll selection of construction materials and springs of accurate
I ¦¦ spring constant k. The design is intrinsically simple for high
I ¦ volume, low manufacture. It can be made of biocompatible material
! and.covered with a thin silicone rubber enclosure.
¦ It is understood that many variations of the basic
concepts disclosed in Figures 1, 2 and 3 are possible and
~ included in this disclosure. The sensor may have only one
¦I diaphragm, whlch feels ¦(ICP)On one side and ~ATh)o~ ~he other.
. - . ' .
:~, ,. , ' ~ '
- '
.
. ~ . ' - . ~ ~ ' ,. '
'
~ L
Ii 1079086
The movable element, equivalent to 6 in Figure 1, may be attached
to the single diaphragm and the displacement of it and the
diaphragm is detected externally. In the dual motion-coupled
diaphragm design, the diaphragms 7 and 7' may not be stacked as
in Figure l, but located at more remote separation. The coupling .
element.6 may be a rigid mechanical means such as a cylinder or
linkage, or may be a fluid transmitted through the body by a tube
or channel. The physical characteristic of the sensor which is
changed and detected with change of differential pressure~P =
~ICP~- ~(ATM~may be diverse, and accordingly, so may be the .
detection means. For example, referring to Figure l, the body 5
and movable element 6 may be scatterers or absorbers of mechanica ,
acoustic, or ultrasonic waves or of electromagnetic waves such as
micro waves or infrared radiation and the external detection
system 10 may involve a source, interferometer, echo detector,
frequency or amplitude detector of these waves by which the
configuration or displacement of 6 relative to 5 may be determined .
Unlike the design of Figure 2, the sensor may contain active
circuits with stored energy cells or induction power circuits.
Ma~y variations of the passive L-C circuit system of Figure 2 and
3 are possible, involving other kinds of variable inductors,
variable capacitors, both variable inductors and capacitors, or
4Fi4ble resistors to cha ~le the r-~onant Srequency or impedanc-
11 . 1 :
I ~ ~ . 6.
.. . . . .
.
.
. ~ . - ~ . :
. ~
Il ~` ~
1 1 !
1079086
., I ..
with pressure. Wide latitude is possible in choice of geometry, ~-
¦ size, configuration of components, coil and ferrite geometries,
¦¦ and frequency of the design of Figure 2. The magnetic slug may
be replaced by a conductive metal slug to achieve induction chang~
by eddy current detuning. The coil spring 16 may be replaced by ¦
, a leaf, lever, or strap springs affixed to the body 5 at one end
and to thé movable cylinder 14 plus 15 in Figure 2 or 6 in Bigure
l. The diaphragm or diaphragms may be convoluted as a speaker or
I rolling diaphragm or as a usual cylindrical bellows to achieve
l0¦ flexibility. The diaphragm may be metal or metal-coated or-made
¦ of a variety of strong, impermeable, and flexible materials.
¦ Initially, the inner spaces of the sensor may or may not contain
¦ fluid. If fluid is used to fill the inner spaces or to act as
! diaphragm coupling, a simple way of insuring that its amount will
151 remain constant is to make it a water solution of the same ionic
concentration as the cerebrospinal fluid and intracellular fluid.
In this way, the osmotic pressures are equal inside and outside
the sensor and the net diffusion flow across the diaphragms will
be zero.
¦ Other specific embodiments of the invention concept of
; Figure l are possible in which substantively different external
coupling means from that of Figure 2 are used. Figures 4 and 5
illustrate an example of a sensbr which incorporates an L-C
¦ resonant c1rzu~ s1m11ar that ln ~1gure Z but dlfferent
7.
'' ' - , ', ,
~ ' , ' . ' .
' ~
~, :
` ~ . --
ll 1079-086
~ '.'
I method of electromagnetic coupling across thé skin 9 to the
I external detector system 10; The coupling method is transcutaneous
capacitive coupling and is done by area electrodes 22 and 22' near
I the upper surface of the sensor. These are in proximity to
¦l electrodes 23 and 23', respectively, on the skin. At the L-C
¦¦ resonant frequency the capacitive reactance of these pairs of
I ad~acent electrodes is small, and thus one can use the resonant
. ! frequency of the implanted L-C circuit to determine the¦ frequency o~ oscillation of an external strongly coupled oscillatc ~r
¦ housed in 10 which can then be measured by the analyzer-readout
console. This type of sensor coupling has several important
advantages. First it allows a nearby stable and fixed coupling,
and circumvents thé possible problems of holding pickup coil 19
of Figure 3 near the sensor 18. In addition, it would allow for
lS ¦ a compact transmittor system in 10 so that the intracranial
pressure information may be telemetered to a remote monitoring
console, while the compact battery operated oscillator is carried
along with the patient or animal under examination. Thus the
design of Figures 4 and 5 represents a unique system with all the
advantages of the concepts of Figures 1, 2 and 3 as well as the
capability of performing intracranial pressure studies and
¦ monitoring a great variety of sub~ect activities.
It is understood that variants of the transcutaneous
~¦ couplin~ scùeme of ~isur- 4 and S are a~s d in this disclosure
_ .
. .... .~ - ` , : ; 1-
. '; . . . ~ ~ :
'
, ' - '
,. '. . ' ' '
~079086
Ij For example, whereas in Figures 4 and 5 an inductor L and capacitor
!~ c are built into the sensor, either one of which or both of which¦
may vary with pressure, it is also possible that only the pressure
¦¦ sensing inductor L, or capacitor C, may be in the implanted
1I sensor, and that the other element of the L-C circuit, C or L
, respectively, may be in the external system 10 along with the
¦ strongly coupled oscillator.
Referring to Figure 6 the variable pressure sensing .
¦ inductor 24 is coupled transcutaneously by area electrode~pairs
1l 22 and 22' and 23 and 23' to an external capacitor 25 which is
il integrated into the active external oscillator system that is
contained in the external detection system 10. The frequency of
¦ oscillations of the external oscillator in 10 is determined by
the L-C circuit made up of 24 and 25 and thus determines the
lS 1l balance condition and intracranial pressure which is read out by !
!i }o. I
il Referring to Figure ?, the implanted sensor contains the¦
¦ pressure sensitive capacitor 26, and the external active oscillator
¦1 in 10 contains the complementary inductor 27.
1, Referring to Figure 8, the transcutaneous coupling is
shown to be inductive rather than capacitive. The implanted L or
, C may be pressure sensitive, or the implant may contain only
r o=ly C analogo=sly ~o g=re 6 and ~ig=Fe 7. rhe impla
I . ' ' .
. '' ~ .1 '', ','.'19'.'" ,. ' .'
-: : : ~ ' ' . - _
,. j
- . -
- -
,: '. ' ~ ~ .
1079 86
I
coil 28 is coupled to external coil 28', thus achieving the necessary
coupling through the skin to the external oscillator in 10. AgainJ
as in designs of Figures 5, 6 and 7 the frequency of the external ¦
oscillator is determined by the L-C value of the pressure
sensitive tank circuit.
Other embodiments of the basic designs disclosed above
can be devised for other types of pressure measurements within the
body and head. To take as illustrative examples in the case of
measuring intracranial pressure, the present invention can~be used
in conjunction with other functional devices, such as catheters,
valves, shunts, flushing devices, reservoirs, filters, anti-siphon
devices, and so on, to form a more diverse or multi-purpose
¦intracranial pressure monitoring and control system. Some importar t
¦illustrations are given below.
¦ Referring to Figure 9, the invention is shown connected
Ito a ventricular catheter 29, which penetrates the brain 3 to the
tdepth of the ventrical space 30 and samples the cerebrospinal fluid
131 therein through the holes 32. This device would then measure
¦intraventricular fluid pressure. The catheter is usually made of
Isilicone rubber and is an integral continuation of the encapsulatic n
¦of the pressure sensor. Some variations in the designs of Figures
¦1 and 2 are also included in Figure 9. A single diaphragm 7 is
¦u-ed and attached to ~ ferrite or gne~ic cvlinder 1~ with a
. , . . , .
',' '''. .,'' , ' ' ' . . ,,
~ 20.
. - -~ _
,
,
.
~ ' -... ~
.. .' . ' ' ' ' : .
1 ~079086
., I
l . .
¦ thinner geometry of the coil 12 and sensor body 5. The magnetic
cylinder may be spring loaded with its equilibrium position on
¦l the shoulder 11. In operation the hydrostatic pressure of the
¦j ventricular cerebrospinal fluid is transmitted to the inner side
¦1 of the diaphragm 7 and the opposing atmospheric pressure is
,1l transmitted through the skin to the outer side of the diaphragm,
and the magnetic slug's displacement is proportional to the
difference in pressures. The barometric compensation, zero
checking, and other features of the sensor of Figures 1 and 2 are
the same. Such catheterization makes measurement of pressures in
other parts of the body readily possible.
Referring to Figure 10, the pressure sensor invention is
attached to a ventricular cathetor 29 lin Figure 9] and the sampled
¦ ventricular fluid 31 is shunted past the sensor to the heart or
1 stomach by a distal cathetor 33. A valve 34 is actuated by the
¦¦ lower diaphragm 7 so that as ventricular pressure rises the
magnetic sluq 14 and motion coupled diaphragms 7 and 7' move
upward and the valve 34 increases its opening allowing more fluid
to be shunted from the brain. Also shown is element 35, in serie
with the pressure monitor-shunt, which may be an on-off switch,
reservoir, or one way flow control as usually bullt into systems
for controlling hydroce phalus.
Referring to Figure 11, the diagram illustrates the
i~ en ~ e~ re~r~ ~n~ o
.. ~ 1
~ ':
'- . , ' :
. . .
~0790~ b
relative internal pressures within the body. Cathetor 29
communicates pressure of fluid pressure in the brain to the
- chamber 34 to the lower side of flexible diaphragm 7 which is
attached to, and actually envelopes in Figure 11, the magnetic
, material slug 14. The coil 12 is embedded in the body and the
spring may be a flat spring also embedded in the body, or the
sensor may rely on the elasticity of the flexible diaphragm 7
itself to provide the spring constant. Another cathetor 33 is
attached to the body 5 and communicates pressure from a second
anatomical region, such as the heart or peritoneum, to the upper
chamber 35 and the upper side of flexible diaphragm 7. In
operation a difference in pressures in chambers 34 and 35 would
result in a force imbalance on 7 and 14 and the consequent-
displacement would be detected by an external detector system.
Manual pressure on the skin 9 above the implanted sensor can
deflect the outside wall 36 of chamber 35 causing it to indent so
as to bring magnetic slug 14 against a seat or stop (not shown).
Thus, the zero-point of the differential pressure sensor can be
calibrated at any time after implantation.
Referring to Figure 12, there is shown another
configuration of the invention, used as a differential pressure
sensor and combined with a fluid shunt valve and a fluid regulato
or zeroing device 37. As in Figure 11, the cathetor 29 communica es
brain fluid pressure to chamber 34 and flexible diaphragm 7 as -
well s
. " , ' , ~ .
:`, ' , ' .'. : . "'' ,:
: . . '
22. _
... . ~
. -- ' ' . '' ` ' ' ' ' '' 1
.
.. . . . . . . .
, ., , , . .~ . :: - , .-. .
1~7908~
to the fluid shunt valve 35; and cathetors 33 and 33' communicate
fluid pressure from another region, such as the heart, to the
flexible diaphragm 7' and chamber 36 and carry exiting fluid away
from valve 35. The difference in pressures are measured by the
displacement of 14, 7, and 7' relative to coil12 as described
above. This integral system thus serves to measure and regulate
flow. In addition, device 37 interposed in cathetors 33 and 33'
serves to allow an external pressure to be applied on the fluid
in 33 and 36 so as to zero, the dual diaphragm system 7, 7', and
14. Device 37 may be, for example, a double domed flexible
rubber reservoir which enables by a digital pressure through the
skin closure of passage between 33 and 33' and subsequently, be a
second manual pressure, an increase in the pressure in 36. Devi
37 could also be a feedback controlled valve or switch, which,
upon sensing the differential pressure across 34 and 36 by the
external detector 10, a controlled feedback is used to actuate a
valve in 37 in such a way as to drive the differential pressure
in a desired direction. This feedback process could be carried
out automatically by an electro-mechanical servo system or by
manual manipulation on the skin.
Referring to Figure 13, another embodiment of the
invention is illustrated for which the pressure communicated to
the upper flexible diaphragm is supplied by a closed fluid system
rather than directly across the adjacent skin as in Figure 2. In
Figure 13 a s~mi-rigid ho ~ g 3- covers diaphragm 1 with a
,,. ..,,, ,' '. .
23. _
' 1,~_ ,,,
,, - , - ~ , . ' . . -
-. : , :.:
: . , .- : .
- ,, , ~ :
. ~ L
space between them. The housing 38 is connected by a tube 40 to
a second housing 41 which lies flat against the skull and which
is covered on its upper side by a third flexible diaphragm 7",
this communicating with the skin above it and thereby with the
atmospheric or any other externally applied pressure on the skin.
A fluid fills the volume 39, the tube 40, and the space 42 inside
41. The system is then a triple motion-coupled diaphragm
arrangement. The first two diaphragms 7 and 7' plus the magnetic
piston 14 and coaxial piston 15 act the same as described~above,
and the differential pressure on 7 and 7' is sensed by an externa
; detector system. The pressure applied against 7' is now trans-
mitted to it by the fluid-filled system comprising 38, 40, 41,
and 7". Barometric compensation again is automatic since
atmospheric pressure on the skin above the third diaphragm 7" wil
be transmitted through the fluid to 7'. An applied external
pressure on the skin above 7" will also be transmitted to 7'; and
this could serve (a) to zero the magnetic piston 14 plus 15 and
thus check the zero-point of the entire system, or (b) to supply
a known and calibrated external pressure to 7' so as to balance
the internal pressure on 7 and thus measure it by a pressure
nulling method.
A configuration similar to that in Figure 13 is possible
I where only two flexible diaphragms are used and the differentiai
~r-s~urc impla=t is catb~ sized ~ _su~e a re ~e press~re i=
~4 ~ ~
..
: ~ -- .
.' . , _ .
.~. . ~ . . . , . ' . .
-:
. . ~ . . -
.
1079086
the ventricles, as was illu~.ra~ed in Figures 9 and 10.
Figure 14 illustrates a unified serial combination
of the invention with a fluid shunt valve. This is
similar to that in Figure 10 except the differential
pressure sensor acts only as a pressure measuring device
and not as a variable valve too. The configuration is
more compact and requires a smaller hole in the skull.
Having described in detail various embodiments
of my invention, it will now be apparent to those skilled
in the art that numerous modifications can be made
therein without departing from the scope of the invention
as defined in the following claims. For example,
external manipulation of the diaphragm can be achieved
by fluidly coupling a pressure source to the diaphragm
by means of a fluid filled tube extending through the
skin to the diaphragm.
mb/Jo - 25 -
:: . . . - . - , :-
.: . :. : .: :
:.. - : ~
. : ,~ - :
