NON-INVASIVE NUCLEAR DEVICE FOR COMMUNICATING PRESSURE INSIDE A BODY TO THE EXTERIOR THEREOF

DISPOSITIF NON INVASIF POUR CAPTER LES PRESSIONS A L'INTERIEUR DE L'ORGANISME

English Abstract

ABSTRACT OF THE DISCLOSURE

The present invention provides a pressure sensor
apparatus for indicating pressure in the human body, particularly
intracranial pressure, comprising a housing, bellows supported
within said housing, wherein said bellows defines a first chamber
and a second chamber within said housing, a fluid filled within
said first and second chambers, means for placing said first
chamber in communication with said pressure to be sensed so that
said pressure will cause said bellows means to contract and
expand, means contained within said housing for communicating
the contraction and expansion movement of said bellows means,
said communication means having at least two components, the
first of said two components being operatively connected to said
bellows and movable therewith when said bellows expands and
contracts, the second of said two components positioned within
said first chamber and being operatively associated with said
first component but not movable with said bellows so that the
relative movement of said first component with respect to said
second component varies as a function of said pressure, said
communication means being adapted to being sensed by a sensor
means located at a remote position from said housing and free of
any physical interconnection with said housing for sensing the
relative position of said first and second components to provide
data indicative of said pressure. In a preferred embodiment, the
first and second components are provided by a radioactive source
and an associated shield, the radioactive output varying as a
function of the relative positions thereof.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A pressure sensor apparatus for indicating pressure
in the human body, particularly intracranial pressure, comprising
a housing, bellows means supported within said housing, wherein
said bellows means defines a first chamber and a second chamber
within said housing, a fluid filled within said first and second
chambers, means for placing said first chamber in communication
with said pressure to be sensed so that said pressure will cause
said bellows means to contract and expand, means contained within
said housing for communicating the contraction and expansion
movement of said bellows means, said communication means having
at least two components, the first of said two components being
operatively connected to said bellows means and movable therewith
when said bellows means expands and contracts, the second of said
two components positioned within said first chamber and being
operatively associated with said first component but not connected
to, nor movable with said bellows means so that the relative
movement of said first component with respect to said second
component varies as a function of said pressure, said communica-
tion means being adapted to being sensed by a sensor means located
at a remote position from said housing and free of any physical
interconnection with said housing for sensing the relative
position of said first and second components to provide data
indicative of said pressure.
2. A pressure sensor as claimed in Claim 1, wherein the
first of said two components is a radioactive source, the second
of said two components is a radioactive shield, whereby
relative movement of said source and shield causes a variation in
the radioactive output therefrom as a function of said pressure.
3. A pressure sensor as claimed in Claim 1, wherein the
first of said two components is a radioactive shield and the
second of said two components is a radioactive source, whereby

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relative movement of said source and shield causes a variation
in the radioactive output therefrom as a function of said
pressure.
4. A pressure sensor in accordance with any one of
claims 1 to 3 wherein ambient pressure responsive means are pro-
vided communicating with said second chamber for transmitting
ambient pressure to said bellows means in the direction of the
urging force of said bellows means.
5. A pressure sensor in accordance with any one of
claims 1 to 3 wherein said pressure responsive means includes a
pressure sensing device of flexible material for insertion in the
body cavity and a pressure-transmitting fluid in said pressure
sensing device communicating with said first chamber for trans-
mitting the pressure in said body cavity sensed by said pressure
sensing device to said housing interior.
6. A pressure sensor in accordance with any one of
claims 1 to 3 wherein said pressure sensing device comprises a
substantially planar member of flexible material having an
interior and a neck portion having one end communicating with
said housing interior and the other end with the interior of said
planar member.
7. A pressure sensor according to claim 2 or claim 3
wherein said radiation shielding means includes a window for said
radioactive source.
8. A pressure sensor according to claim 2 or claim 3
wherein said radioactive source is a solid mass.
9. A pressure sensor according to claim 2 or claim 3
wherein said radioactive source is a solid mass of promethium 145
in a binder.
10. A pressure sensor in accordance with claim 1
wherein said pressure responsive means includes as
a fluid conduit formed of deformable metallic material to permit

19

said conduit to be shaped to the contours of the body portions
adjacent said body cavity.
11. A pressure sensor in accordance with any one of
claims 1 to 3 wherein at least part of said pressure responsive
means is formed of a silicone rubber material and includes a
pressure-transmitting fluid selected from the group consisting of
castor oil and mineral oil.
12. A pressure sensor in accordance with any one of
claims 1 to 3 wherein said pressure responsive means includes a
silicone oil as a pressure-transmitting fluid and wherein at
least part of said pressure responsive means is formed of an
elastomeric material selected from the group consisting of butyl
rubber, neoprene rubber, butadiene rubber and fluorelastomer.
13. A pressure sensing device in accordance with any
one of claims l to 3 wherein said pressure responsive means is
formed in part from an elastomer and includes as a pressure trans-
mitting fluid a similated cerebrospinal fluid.
14. A pressure sensor according to claim 2 or claim 3
wherein said radiation shielding means defines a gap in the repose
condition which gap is incrementally exposing said radioactive
source with infinite resolution.
15. A pressure sensor according to claim 2 or claim 3
wherein said radiation shielding means and said radioactive source
are slidably arranged in loose fitting relationship to define a
flow passage therebetween.

16. A pressure sensor according to claim 1
further including means for securing said sensor to a

portion of the body whose pressure is being monitored.
17. A pressure sensor according to claim 16, wherein
the securing means is a tab having an intermediate portion of
arcuate cross-sectional shape for accommodating said housing in

underlying clamped engagement therewith and fastening means to


secure said tab to the body portion.
18. A pressure sensor in accordance with claim 17
wherein said means for securing is formed at least in part of
tantalum.
19. A pressure sensing apparatus in accordance with
claim 10 wherein said fluid conduit is formed of titanium.
20. A mounting arrangement in accordance with claim
17 wherein adhesive means are provided to secure said tab to
said housing.

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Description

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. .
. The pxesent invention relates to a pressure sensor ~ ;
~ - ¦ for~u~n~ the pressure in a body cavity. : ;-~ ~ :
: I The need for a non-invasive technique for measuring ..
: the pressure in body cavities of animals or humans is recog- . :
nized as highly desirable for continuous or intermittent moni- I
~' toring of body conditions. Such cavities as the cranium, vena
. cava, bladder and others provide valuable and sometimes critical I
i information for maintaining the well-being or survival.of an :
.... ¦ animal or human. For example, it is known that the intra-
¦ cranial pressure pro~ides a valuable indication of well-being 1~
for a variety of clinical conditions, including shock trauma ~ ; ~ I
. ¦ and hydrocephalus. l ~ ~1
Present-day pressure sensors are intended for perma-
nent lmplantation for non-invasive utilization of~their pressure
sensing function. They do, however, constitute~a foreign. body
whose pressence may create physical problems which must.be obvi~
. ~ I ated for proper functioning of the sensor and for a minimum of
: I discomfort and disfigurement to the patent. For instance, it
. ¦ is highly desirable that the component parts of the sensor ex- .-~
., ternal to the body portion being monitored be firmly and securely .
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mounted as any movement of SUCIl component parts, p~rticularly
when mounted subcu~aneou.sly can produce lrritation and attendant
discomfort to -the patient. It is not uncommon for body tissue
such as tha-t produced by surgical scars durin~ implantation or
muscular grow-th to interfere with the proper operation of the ~ -
sensor by imposi.ng pressures on those parts of the device which
are designed to be responsive to pressures such as ambient pres- ;
sure. ~hen such a sensor is used pa.rticularly for pressure -~ ~
. sensing of the intracranial cavity, the pressure transmitting :
fluid conduit communicating with the pressure sensing device in m
~ the cavity can easily impose pressure on the brain, the sensitive
`` tissue of which can be easily damaged. Furthermore, since such ~ -~
I pressure sensin~ apparatus should be devoid of deterioration
.' during its useful Iife, which may be for a period of many years,
it is highly desirable that the component parts be completely :~
~ compatible and/or inert chemically and physically with the
`, adjacent body portions so as to avoid any adverse reactions.
-. : Additionally, the component parts of the apparatus and pressure
:~ transmitting fluid whlch are in contact should be completely
~ 20 ~compatible so as to avoid any deterloratlng reaction therebetween.
In addition, leakage between the component parts is to be
avoided, but should there be a failure, the fluid should be

: : , :
compatible~in the event of leakage. Furthermore, the parts
should remain in perfect working order throughout the useful ~ ~
life of the apparatus. Since such a pressure sensor uses -` :
radioactive matqrial, such radioactive material should be of the
~ type which requires no replacement during the useful life of the
il~ sensor and it should function in a manner which is non-injurious
. ~ to the body and to provide a radioactive output in a highly
;-~ 30 accurate and uniform manner so as to reflect with extreme

.~ precision, the sensed body fluid pressure throughout its range
of operation under both positi~e and negative fluid pressures.



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The no~-inyasive nuc].eqr device o~ the present invention
is fully irnplantable and is full~ cap~ble of col~nunica-tiny
pressure inside a body to the exterior thereof to allow read out
non-invasively. In its pre:Eerred form, the invention includes . .
a housing ~or subcutaneous lmplantatlon with the radioactive
source contalned ln the housln~ lnterior and appropriate
radiation shield means disposed about the radioactive source.
Urging means such as a bellows are provided in the
housing interior which yieldingly ur~e the radioactive source and
shield means .into a predetermined shielding ralationship, the
fluid pressure from a fluid pressure sensing device inserted in :
the body portion being monitored being transmitted to the housing
interior by means of a pressure transmitting fluid through a
conduit to move said radioactive source agalnst the force of the
urging means out of the inltlal or repose shielded relationship
with the shield means proportionallv with an increase in pressure
in the body portion being monitored to produce a radioactive :
:~ output from the radioactlve source corresponding to the magnitude ~ ~
Qf the pressure in the body portion. In one embodiment, the ; ~:;
- 20 housing is securely mounted on a supporting portion of the
~ ~ body such as a bony structure for permanent implantation under .`.;~
.. the skin, the mounting means serving as a shield for
. , .
radiation directed towards the body and to confine the radio~
~ .
active output to a limited external detection area.
When the inyentive device is inserted within a body
`;: portion, such as the intracranial cavity, the deformable metal
tube may be shaped in accordance with the contours of the body
portion thereby avoiding any pressure and attendant injury to
; adjacent bod~ portions such as the brain. To compensate for
changes in ambient pressure, an ambient pressure sensor is

mounted on the housin~, the interior of which is filled with a
preSsure transmi'cting fluid for transmitting the sensed change in ~:


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ambient pressure to the urc~in~ ~eans in o~posi-tion to khe ~ ;
pressure exerted on the urginy means. This am~ient pressure
sensor includes an annular peripheral portion and a recessed
centex por-tion to limit -the imposition of pressure on the
device by scar tissue or ~uscular contraction and even
concentrated loads such as externally applied forces.
The invention also includes a new and novel radioactive `~
composition to produce a highly accurate radioactive output
throughout both the useful life and range of operation of the
invention thereby accurately reflecting the true pressure
conditions within the body portion being monitored, the radio~
actiye output being of a level whlch is virtually totally non~
injurious to the body.
Thus, the pressure monitoring apparatus of the invention
may be simply and easily mounted on or within a body in a
concealed, non-disfiguring manner and in a permanently installed
position throughout the treatment term of the patient producing
virtually no injurious effects on the patient yet producing high-
ly accurate body pressure reaaings throughout its life and with-

out mechanical deterioration or malfunctioning and with only
~slight decay of the radioactive output which is easily compensated
for thus eliminating the need for replacement and its attendant ;
sur~ical problems.
~;i Figure 1 is a perspective view of a preferred embodiment
., ~:
of the non-invasive nuclear apparatus of the invention in an

~j installed position for monitoring the pressure in an intracranial ;
. . . .
cavity and communicating the monitored pressure to the exterior
of the body;

; Figure 2 is a plan view of the apparatus of Figure l;
Figure 3 is a sectional VieW taken substantially along
line 3~3 of Figure 2 in the direction of the arrows;
Figure 4 is an enlarged sectional view of a portion of



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the apyaratus o~ 3ure 3;
Figure 5 is an enlar~ed perspective yiew oE the mounting
arran~ement lor the apparatus of Figure l; ~:
Figure 6 is a perspective view of a portion of the skull
of a patient prior to installation of the apparatus of the
invention;
.~ Fi~ure 7 is a sectional view taken substantially along
~ lines 7-7 of Figure l in the direction of the arrows;
: Figure 8 is a vertical, cross-sectional view of another
.~ lO embodiment of the pressure sensor apparatus of the present inven~
tion; and :~
Figure 9 is a plane view, partly ln section, of one of
; the flexible tambours a portion of which is shown in Figure 8.
eferring now to the drawings and to Figures l and 2 in
particular, there is shown the pressure sensing apparatus of the
invention with a housing designated generally by the numeral lO,
` and fluid pressure responsive ~eans designated generally by the :~
numeral ll and connectea to the housing lO for sensing the fluid
pressure in a body portlon such as a cavity. Ambient pressure - .: .
~l 20 responsive means, designated generally by the numeral 12, is also
-/~ provided on the housing 10 which is responsive to ambient pressure
to compensate for changes in ambient pressure during the ;~:
operation of the invention. Although the pressure sensing
apparatus of the invention is shown in an installed position on ~ ~.
.~- the head of a human body fornon-invasively monitoring intracranial
i cavity pressure and communicating it to the exterior, it should .
` be understood that this is only a preferred example of the
. invention and that it is equally adaptable for monitoring fluid
pressure in other areas o~ the body~ both animal and human.
Therefore, while the description to follow will be directed to
the use of the inyention for monitor~ng intracranial cavity
. pressure, it should be understood that the invention is equally

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applicable ~o m~nitoriny fluid ~es$ure ;n other body portions
and cavities.
Referring now to Flgure 3, and as specifically illus-
trative of the inven-tion, the housing 10, which is formed of
titanium, is preferably of tubular shape having a side wall 13
defining an interior 14. A :Eirst support member 16 formed of
titanium having a central bore 17 is positioned within one end ~;
of the housing 10 in sealing relationship with the housing side
wall 13 by means of an epoxy resin or the like. PreEerably, an
annular shoulder 13a is formed in the housing side wall 13 for
positioning the support member 16 in a precise location within
the housing 10 as will be explained hereinafter. The first ;
support member centraI bore 17 is provided with a first portion
17a of slightly enlarged diameter and a second portion 17b of `~
substantially enlarged diameter defining a recess 20 which
communicates with the interior i4 of the housing 10.
The fluid pressure responsive means 11 includes a fluid
conduit 22 of deformable metallic material preferably titanium ~
which has been heat treated ror deformability, one end 22a which `
is arranged to be connected to a fluid pressure sensing device or
tambour 23 having an interior 24 which is arranged to be position-
ed within a body cavity such asthe intracranial cavity of Figure



The tambour 23 is formed of a suitable elastomeric
material such as medical Grade Silastic rubber and is of a sub-
stantially flat configuration including a neck portion 25 in the
wall of which is molded a helical spring 26 preferably of stain-
less steel for imparting rigidity to the neck portion 25. The
neck portion 25 includes a central bore 25a which communicates

with the interior 24 of the tar~our 23 and which is arran~ed to
receive the end 22a of the conduit 22 as shown in Figure 2.
~referably a U-shaped clip 27 of tantulum or the like is disposed


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10S~4Z4

within the interior 24 of ~he tambour 23 ~or maintaining the
side walls of the tambour ln spaced-apart relationship and to
serve as a loca-ting means for the tambour wlth the use of x-rays.
he tambour or fluid pressure sensing device ~3, the fluid
conduit 22 and the communicating portions of the housing interior
14, including the recess 20, are filled with a pressure trans- ;
mitting fluid through which the pressure sensed by the tambour 23
in the body cavity is transmitted to the housing interior 14. ~ '
The other end 22b of the conduit 22 is swaged to a
suitable enlarged ou-ter diameter so as to confirm generally to ~ '
the inner diameter of the enlarged portion 17a of the first ''
support member central hore 17. The conduit end 22b is press- ~ ,
fitted into the bore portion 17a with the conduit 22 extending -~
through the bore 17 as shown best in Figure 3. Sealing engage-
ment between the conduit 22 and bore 17 is obtained by means of ,~
epoxy resin. Thus, the conduit end 22b communicates with the
recess 20 and with the housing interior 14.
A source 29 of radioactive material preferahly in the ~ ~
form of a shaped article is disposed within the housing interior ~`
14 together wlth radiation shield means designated generally by
the numeral 31., Means are provided in the housing interior 14
for'yieldingly urging into a shielding relationship. More
specifically, urging means such as a bellows 32 having an '~
interior 33 is disposed within the housing interior 14, one end
32a of which is moun-ted on a necked-down portion 34a of a second
support member 34 preferably formed of titanium and suitably
mounted in the other end of the housing 10 in sealing engagement
with the housing side wall 13 by means of an epoxy resin or the
like. The other end 32b o~ the bellows 32 is closed as ~ill be
explained hereinafter.
The second support member 34 is provided ~ith a central ;'~

bore 38 and the necked-down portion 34a is arranged to support

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the bellows end 32a in a sealiny relationship therewith by means
of an epoxy resin 41 or the llke.
The central bore 38 of the second support member 34
includes a portion of enlarged diameter forminc3 a recess 42 and
which is provided wi~h an annulax, inwardly directed flange 43.
The recess 42 receives and nipple 44 having a central passage 44a
of an ambient pressure sensor or tambour 46 forming the ambient
pressure responsive means 12. The tambour 46 is formed of a
flexible material, preferably an elastomeric material such as
medical Grade Silastic rubber, and includes an annular peripheral
portion 47 and a recessed central portion 48 defining an interior
49 extending through the nipple central pa~ssage 44a.
A suitable adhesive such as a medical Grade Silastic
adhesive, seals the nipple 44 in -the recess 42 and the annular
flange 43 compresses the outer surface of the nipple 44 to form
a mechanical compression seal to securely retain the nipple 44 in ~ -

~`l the recess 42. ~ ;
A rigid metal tube 51, preferably formed of titanium ;
is also sealed in nipple 44 and by a Silastic adhesive and
' ~ 20 extends through nipple central passage 44a and the central bore -
~38 of the second support member 34 into the bellows interior 33
- to communicate the interior 49 of the tambour 46 with the bellows ~ -
~ '
32. The other end 51b of the tube 51 forms a stop for the

bellows end 32b.
.,.: . :
In order to transmit the sensed ambient pressure to the
interior of the bellows 32~ the interior of tambour 46, the
bellows interior 33 and the tube 51 are filled with a pressure
transmitting fluid, isolated by means of the bellows 32 from the

~l pressure transmitting fluid in the fluid pressure responsive
`l 30 means 11. In the preferred embodiment, all o the exposed ;~
metallic surfaces of the sensin~ apparatus of the invention are
coated with a suitable biocompatible material, such as a medical ~ ;

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~57424

grade Silastic adhesive. As shown in the drawings, ~his
Silastic adhesive 50 extends from the n;pple ~4 of tam~our 46 to
the joint between the metal conduit 22 and the neck portion 25 of
tambour 23.
In the illustra-ted embodiment, the radiation shield
means 31 includes a first portion 53 of radiation shileding
material such as tantalum having a cup-shaped configuration. The
first portion 53 preferably includes an end plate 54 preerably
in the form of a disc and an annular slde member 56 both mounted
on the other end 32b of the bellows 32 in closing relationship
therewith as shown best in Figure 4.
The radiation shield means first portion 53 is mounted
on an inwardly directed channel poriton 57 adjacent the last
accordion pleat in the bellows 32, and a tubular sleeve portion
; 58 extending axially outward therefrom which together define an
enclosure 59. The end plate 54 is adhesively secured in the end
of the enclosure by a suitable adhesive such as an epoxy resin
closing the end 32b of the bellows 32. Similarly, side member 56
is adhesively secured by means of an epoxy resin to sleeve
portion 5~.
- The radiation shield means also includes a second ;~
i ,
portion 61 in the form of a tubular sleeve of radiation shield :
;~ material, also preferably tantalum which is press-fitted or the
; like within the recess 20 of the first support member 16~ It can
~ be seen that the second portion 61 extends throughout the depth
-~ of the recess 20 and has a fo~ard end edge por-tion 61a termin-
ating flush with the end of the first support member 16 abutting
the housing side wall shoulder 13a. Thus, the second portion end
61a is precisely positioned axially in the housing interior 14
adjacent the end edge portion 56a of the first portion side ~ ;
member 56.

Radioactive source 29 is mounted on the end 32b of the




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1~57~

bellows 32 and is slidably accommoda~ed for yuiding movement
within the radlation shield means second portion 61 di.sposed in
the recess 20. The radioactive source 29 which .is preferably of
cylindrical shape, having an outer diameter conforming generally
to -the inner diameter of the bellows sl.eeve portion 58 is `
; adhesively secured within the enclosure 59 defined by -the
tubular sleeve portion 58 by means o~ a suitable adhesive such
as an epoxy resin. The end cap 62 haviny a meniscus 62a is form-
ed by the adhesive material.
The bellows 32 yieldingly urges the radioactive source
, .
29, together with the sleeve portion 58, in the direction of the
. ~
arrow I into the recess 20 with the edge portion 56a of the
radiation shield means first portion side member 56 in adjacent
cooperating relationship with the edge portion 61a of the tubular
sleeve forming the radiation shield means second portion 61 to : . :
establish a shielding relationship with the radioactive source 29. ~
The end cap 62 is therefore disposed oppositely the outlet end :~ :
. !
22b of the pressure transmitting fluid conduit 22. .

~- The outer diameter of the bellows sleeve portion 58 is

selected to produce a loose-fitting relationship with the inner

surface of the sleeve forming the radiation shield means second

~ portion 61 so that fluid introduced into the recess 20 from the

; end 22b of condui.t 22 may flow freel~ therebetween and through a


`' gap between the front and second portions end edge portions 56a

~ and 61a respectively to fill the interior 14 of the housing lO

. on the outside of the bellows 32.

It should be understood that in the assembled apparatus :

~ of the invention before installation in a body there is virtually

;, no pressure differential in the housing 10 between the pressure ~:

, 30 transmittiny fluids on opposite side of the bellows 32. In this

:. condition, there is a gap between the adjacent end edge portions ~ ~

~ 56a and 61a of the first and second portions 53 and 61 respec- : ,


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tively. When the apparatus is installed .in -the body, the normal l;
fluld pressure in the body cavity slightly lncxeases the pressure
on the tambour 23, in-troducing additional pressure transmitting
fluid into the housiny interior 14 on the ou-tside of bellows 32, t
~ moving the bellows in the direction of the arrow D, -thexeby
lncreasing slightly the gap between -the end edge porti.ons 56a
and 6la.
In the operation of the invention after installation, . ..
an increase in fluid pressure is sensed in the body cavity by
the fluid pressure sensing device or tambour 23, the sensed
pressure is transmitted by the pressure-transmitting fluid flow~
ing into the support memher recess 20 -through the end 22b of
. conduit 22 around the end cap 62 through the gap between the
edge portions 56a, 61a to move the be'lows 32 together with the
radiation shield means first portion 53 and the radioactive
source 29 in the direction indicated by the arrow D in opposition
~' to the urging force exerted by the bellows. During this movement,
the radiation shield means first and second portions 53, 61 move
apart increasing the gap proportionally with the increase in .. ~
. 20 cavity fluid pressure thereby modifying the shielding relation- ;1.:
.. ship between the shield means 31 and radioactive source 29 to
. expose more of the radioactive source in accordance with the
magnitude of the cavity pressure. The radioactive output of :
-. the exposed portion of the radioactive source 29 may then be .:.
, :
- sensed by a conventional nuclear counter or crystal detector
disposed externally of the housing 10 and the body.
The provision of the ambient pressure responsive means .
12 permits the sensing apparatus of the invention to be respon-
sive to pressure changes in the body cavity regardless of
/ 30 ambient pressure changes, Accordingly, ambient pressure changes . .
are imposed equally on both the ambient pressure responsive ~ ;
means 12 and the cavity pressure responsive means 11 whereby .

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the sensi.ng app.lratus of the invention respond$ to hody cavity
pressure changes only.
To insure a lony life for the sensing apparatus of
the invention commensurate with body compatability, it has been
found that specific non-reactive fluids and elastomeric materials
eliminate such reactions. More specifically, the best results
that have been obtained are when the elastomeric material of the
various components are formed in one examp].e, from a Silastic
type of silicone rubber and the pressure transmitting fluids
are eithe.r castor oil or mineral oil be~ween which there is vir-
tually no chemical or physical reaction whereby insuring proper
functioning of the invention throughout its life. It has also
been found that when the pressure transmitting fluid is a sili-
cone oil, the outstanding results of the invention are accom-
plished when the materials are selected from the group consisting
of butyl, neoprene, suna N (a trademark) and Viton A (a trademark)
rubhers. It should be understood, however, that other elasto~

meric materials and fluids perform satisfactorlly but with less ~ ;
. . .
:~ desirable results.
, .
i 20 One major concern in selecting a fluid is the osmotic
pressure effects produced during implant. It is preferred to
eliminate these effects that a simulated cerebrospinal fluid be
used as the pressure transmitting medium and it may be used with
.~ all materials of construction as it will be compatible with body
~ ~ fluids and will not leak through the elastomeric materials as a ;
: .
-: conse~uence of osmotic pressure. .~
. :.: .
~-: In the use of the invention to monitor the fluid pres- ~ ~ :
~ sure within an intracranial cavity and with reference to Figures ;~
- 5-7, the common practice is to p~ovide a burr hole or aperture
70 within the bony structure of skull 71 overlying the intra~
cranial cavity through which the metallic fluid conduit 22 is ~ .
inserted, the cavity pressure sensing device 23 being suitably


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d;sposed within the intracr,lnial cayit~, The housing 10,
toge-ther with the ambient pressure responsive device 12 are
mounted on the ou-ter surface OL ~he skull 71 under the scalp 72.
The apparatus of the inventlon includes means for per-
manently mounting the housing 10 and ambient pressure responsive
means 12 subcutansously on the outer surface of -the skull 71 in
an inconspicuous, securely retained position. More specifically,
an elongated concave groove 73 is formed within the outer surface
of the skull 71 adjacent the burr hold 70, and mounting means
are provided for securing the housing 10 in a seated relationship
within the groove 73. The mounting means includes at least one, ;~
preferably two, tabs 74 arranged in longitudinally spaced -
, relationship on the housing 10 as shown best in Figure 5. Each
-~ of the tabs 74 includes an intermediate portion 76 of arcuate
. J~ cross-sectional shape for acco~nodating the tubular housing 10 ~-
'~ in underlying engagemen-t therewith. The tab portion 76 is
secured to the outer surface of the housing 10 by suitable means ~ -
such as a body compatible adhesive, welding or the like. The
tabs 74 also include oppositely disposed end portions 77 and 78 'I
extending laterally outward of the housing 10 secured within the
intermediate portion 76.
' Openings 79, 81 are provided in the tab end portions
77 ,78 respectively for accommodating screw means such as screws
~ 82 extending therethrough in threaded engagement with the under-
3~ ` lying bone of the skull 71, and with the end portions 77, 78 in
;~ overlying engagement with the outer surface of the skull 71, the
! . . . ~
tab intermiedate portion 76 and housing 10 being accommodated ~ -

within the groove 73.
::
In the preferred embodiment, the tabs 74 are preferably
formed of a radiation shielding material such as tantalum. One

of the tabs 74 is positioned on the housing 10 with its

intermediate portion 76 extending throughout the path of movement
'~
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.--
~ ~5~9~24

o~ the r.~dioactive source 61 w.i.thin the hol~siny. Thus, not only
does the one ~ab 74 prevent downwardly directed :radiation into
; the body, but the radioactive output of source 29 ls confined in
a non~attenuating manner to the ul~ward clirection to permit easy
detection by an externally positioned detection device.
The output of the radioactive source 29 need only be of
; an ex-tremely low order of magnitude typically less than 0.1
microcurie, a magnitude far less than that at which the adjacent
body tissue may be adversely affected. However, it should be
characterized by an extremely precise and uniform output rate
which accurately reflects the changes in fluid pressure within
; the body cavity throughout its range of operation. The prefer- :
red radioisotope used in the present invention is Promethium-145
~ and to obtain the proper radioactive output from -the source 29,
i`~ it should be in the form of a shaped article of highly homogeneous ~:
s . composition. Accordingly, another novel feature of this invention
. is provision of such a shaped article of radioactive material.
~; The radioactive source 29 comprises Promethium chloride
,~J (pmcl3) uniformly distributed and absorbed onto an inert carrier
- 20 such as diatomaceous earth and uniformly distributed throughout
:.
a suitable binder such as an epoxy resin. Sources 29Of this
. composition are extremely uniform regarding the concentratlon or
: distribution of the PmC13.
.. Another embodiment is shown in Figures 8 and 9. In this
embodiment, pressure sensor 110 broadly comprises housing 112 and . :.
, flexible containers or tambours 11~ and 116. Housing 112 defines
an interior opening 118 which is divided into two chambers 120 ~.
and 122, respectively, by bellows 124. Chambers 120 and 122 act
as reservoirs for non-radioactive fluid.
: 30 Bellows support 126 is mounted in the end of housing 112

and closes chamber 120. Chamber 120 is fluidly connected to
tambour 114 by means of bellows tube 128 which fits into port 130

. : . .
: -15~

,

:i
105~4Z9~
of bellows suppor-~ 126 and opening 132 in the end o~ tambour 114.
Chamber 122 is closed by radioactive material tube support 134
which is mounted in the other end of housing 112 from bellows
support 126. Chamber 122 is fluidly connected to tambour 116
by means of connection tube 136 which fi-ts into port 138 in
radioactive material tube support 134 and into opening 140 in the
end of tambour 116.
The radioactive material 142 is housed in source tube
144 which is mounted in opening 146 in radioactive material tube
support 134. The open end of source tube 144 is closed by shield
.
plug 148. Surrounding source tube 144 is shield tube 150 which
is connected to bellows 124. Opening 152 in shield tube 150
places the face 154 of bellows 124 in communication with tamoour
116 through port 156 in the body of radioactive material tube
support 134 and annular opening 158 formed hetween housing 112 ;~
.
and radioactive material tube support 134. `
Tambour 116 is li~ce tambour 123 and is filled with a
non-radioactive fluid and is placed in the body cavity such as
the cranium, bladder, or vena cava of an animal or human for
sensing the pressure of the body cavity. Tantalum wire 60 is -
placed in tambour 116 to give it suitable shape and enable it to
be located non-invasively. Furthermore, a coiled spring (not
shown) is placed in neck portion 162 of tambour 116. Tambour
114, like tambour 116, is filled with the same non-radioactive
fluid as tambour 116 and serves to compensate for changes in
ambient pressure. Optionally, tambour 114 can be eliminated, the
end of bellows tube 128 sealed, and chamber 120 filled with gas
or evacuated to indicate absolute pressure Also, for certain
applications, tube 128 can be left open to communicate with the - -
atmosphere.

~lousing 112 as well as bellows support 126 and tubes 128, `~
140 and 144 is preferably constructed of titanium. Bellows 124
i ' "''
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: . : : .: . :, . . - .

~05742A
is preferably constructed of nickel and -typically has a sprlng
ra-te of 0.10 lbs/ln. ~adloactlve material tube support 134,
shieldinq plug 148 and shieldlng tube 150 preferably comprises
tantalum shielding; however, tungsten, iridium, rhenium,
platinum, rhodium, gold, or other sultable heavy me-tals can be
used. All tubing, housing and dlaphragm jolnts are suitably
formed by epoxies, brazing, or the use of sultable gaskets, etc.
Flnally, the entire sensor can be coated with a thin coatlng of
. .
sillcone rubber or placed ln a silicone rubber boot if desired

to assure tissue compatibility.




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