Disposable physiological pressure sensing system

A physiological pressure sensing and monitoring system including a sterile throwaway pressure transducing device. The device includes a pressure transducer mounted together with a flow control valve in a housing. The device includes a first connector for connecting the device to a source of sterile solution, a second connector for electrically connecting the pressure transducer to a monitoring device, and a third connector for selectively connecting the device to a catheter inserted into a patient's circulatory system. The device, including the connectors, is made to be low cost so as to permit the entire device to be installed and discarded as a unit so as to constitute a throwaway pressure sensing and flow regulating means. A number of different embodiments of the pressure transducer are disclosed, each of which constitutes a low cost, accurate pressure transducing means arranged to have high electrical isolation relative to the fluid in a pressure chamber of the housing, the pressure of which is continuously sensed by the transducer. In one embodiment, the force collector for transmitting the pressure force to the strain gage is formed as a one-piece unit. In a number of the embodiments, the elements are formed separately and bonded together.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to physiological pressure sensing systems, and in 
particular to such a system utilizing a disposable pressure transducer. 
2. Description of the Background Art 
An improved flow control apparatus for use in liquid flow systems, such as 
for monitoring of blood pressure in humans and other animals, is disclosed 
in U.S. Pat. No. 4,291,702, of James E. Cole et al, which patent is owned 
by the assignee hereof. As disclosed therein, the flow control apparatus 
is adapted for use with fluid flow catheters, such as used in invasive 
connection as by insertion into a patient's blood vessel. In normal use in 
such systems, the catheter is provided with a sterile isotonic solution 
which is caused to flow through the catheter into the patient at a low 
flow rate sufficient to maintain the catheter open and unclogged as by 
blood cells and the like at the inserted end of the catheter. 
As further pointed out in the Cole et al patent, the catheter system is 
firstly flushed of air before insertion of the catheter into the patient. 
To permit the system to be rapidly filled with the sterile solution which 
is used to flush the system of air, the catheter flushing apparatus of 
said patent further is arranged to selectively permit a high flow rate of 
the solution from the source to the catheter. 
In one embodiment of the structure disclosed in the Cole et al patent, a 
flexible diaphragm is extended across an opening to the pressure chamber 
of the housing of the apparatus. Means are provided for connecting a fluid 
actuated transducer to the housing so that deflections of the diaphragm 
cause corresponding fluid pressure transmissions to the transducer. 
A problem has arisen in the use of such systems relative to the high 
expense and unreliability of the pressure transducers before employed in 
such systems. Such transducers have been quite expensive in order to 
provide the necessary accuracy. As the transducers must be cleaned and 
sterilized from time to time, the useful life thereof has been relatively 
short. Such transducers further have been found to become inoperative as a 
result of the cleaning and sterilization processes. Such inoperativeness 
presents a particularly vexatious problem in that it normally occurs at 
the critical time of setting up the system with the patient as testing of 
the apparatus is normally conducted prior to the cleaning and 
sterilization steps because of the impracticality of testing subsequent 
thereto. 
Further, the use of the reusable pressure transducers may cause 
cross-contamination and spreading of infection where complete cleaning and 
sterilization are not achieved. 
SUMMARY OF THE INVENTION 
The present invention comprehends an improved physiological pressure 
monitoring system which eliminates the high cost and unreliability 
problems of the prior art systems by the provision of an improved 
throwaway component including the fast-slow flow control means and the 
pressure transducer means in a single housing. 
The invention comprehends the provision of the system as a low cost, high 
accuracy transducer effectively permitting throwaway use of the device so 
that the device may be used with a single patient only, thereby completely 
avoiding cross-contamination and infection. 
The invention comprehends that the device further include means for 
connecting the source of sterile isotonic solution thereto and means for 
connecting the patient catheter thereto. 
Still further, the illustrated device includes electrical connection means 
for connecting electrical output means of the pressure transducer to an 
external monitor and the like. 
The invention comprehends the inclusion of the connecting means as portions 
of the throwaway device. 
The means for controlling solution flow from the source, such as an 
elevated bag or container, further includes flow restrictor means which 
maintains the pressure chamber of the device substantially at the 
patient's blood pressure, notwithstanding the continual delivery of 
solution at a low rate therethrough to the catheter for maintaining the 
catheter unclogged, as discussed above. 
The invention comprehends the provision of such a device wherein the 
pressure transducer sensing means is electrically isolated from the fluid 
in the pressure chamber so as to effectively prevent damage to the 
pressure transducer as by application of high voltages and transient 
electrical pulses of 400 to 500 joules such as may be applied to the 
patient in effecting certain treatments thereof. Alternatively, the 
electrical isolation of the transducer from the pressure chamber avoids 
transfer of electrical current from the external monitoring system and, 
thus, effectively prevents fibrillation of the patient's heart, such as by 
a short occurring in the external system. 
The invention further comprehends the provision in the throwaway device of 
pressure relief means for preventing high pressure conditions which may 
appear in the pressure chamber from damaging the pressure transducer. 
The arrangement of the device as a throwaway device permits it to be 
packaged in sterile condition for sterile storage until desired use. At 
that time, the sterile sealed package is opened and the system filled with 
sterile isotonic solution to eliminate any air pockets therein and permit 
facilitated invasive connection to the patient. 
The device provides a complete interconnection system between the source of 
sterile solution, the electrical monitoring apparatus, and the patient, 
and thus, completely eliminates the possibility of cross-contamination, as 
well as assuring that a reliable new system is available for immediate 
use. 
The invention comprehends the forming of the housing and other components 
of the system from low cost molded synthetic resins, such as 
polycarbonate. 
It is desirable that the synthetic resins have high strength, chemical and 
electrical resistance, and dimensional stability. 
In the illustrated embodiment, the pressure transducer utilizes a strain 
gage comprising a diffused pattern on a single crystal silicon beam, it 
being understood that other forms of pressure transducers providing 
suitable electrical signal outputs may be employed within the scope of the 
invention. 
The invention comprehends that the major spring restraint in the pressure 
transducer be provided by the beam. A compliant diaphragm is provided in 
the illustrated embodiment, with suitable link connecting means between 
the diaphragm and beam forming a portion of the force collector structure. 
Calibration of the pressure transducer is effected in the illustrated 
embodiment by suitable trimming of resistors provided in the electrical 
connection means for facilitated, low cost calibration. 
The electrical connector calibration means provides sensitivity 
normalization and thermal error compensation. 
The transducer includes a strain relief and a flexible cable of electrical 
conductors connected to the strain gage by suitable fine wires. 
The invention comprehends the provision of such a transducer wherein the 
member of major restraint is arranged to be self-protecting from 
overpressure, permitting omission of an overpressure safety stop. 
In the illustrated embodiment the connection to the catheter from the 
pressure chamber within the housing includes a multiple connection 
stopcock for selectively connecting the system in a plurality of different 
paths. 
In the illustrated embodiment, the stopcock is formed integrally with the 
housing as part of the low cost throwaway device. 
The invention comprehends the use of different forms of pressure 
transducers mounted in the housing. 
In the illustrated embodiments, the pressure transducers include a force 
collector including a diaphragm, a frame, and a link for connecting the 
diaphragm to the deflectible beam. 
In the illustrated embodiments, the beam is provided with strain gage 
means. In one form, the beam is formed of silicon, with a resistive strain 
gage grid fused thereinto. 
The beam, in the illustrated embodiments, is mounted to the frame by a 
strain isolator for preventing strain which may be induced in the frame 
from affecting the strain gage means. 
In the illustrated embodiment, the external control resistor comprises a 
thin film resistor which is selectively trimmed by a laser trimming 
operation to provide the desired calibration of the pressure transducer. 
The structure of the device is extremely simple so that the elements may be 
formed by automatic manufacturing processes to further reduce the cost of 
the device, permitting the one-time throwaway use thereof. 
Further low cost manufacture is effected in one embodiment of the invention 
by forming the three elements of the force collector as a one-piece unit. 
Further low cost manufacture is effected, in the illustrated embodiment, by 
forming the beam as a wafer element having a thickness of approximately 
0.01 inches. 
The throwaway pressure monitoring device of the present invention is 
extremely simple and economical of construction while yet providing the 
highly desirable features discussed above.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In the exemplary embodiment of the invention as shown in the drawing, a 
disposable, physiological pressure sensing system generally designated 10 
is shown to comprise a device 11 having a housing 12 which, as seen in 
FIG. 3, defines a pressure chamber 13, at one end of which is received a 
flow control valve 14. 
As further illustrated in FIG. 3, housing 12 further defines a transducer 
chamber 15 in which is mounted a pressure transducer 16. Chamber 15 is 
selectively closed by a closure element 17. 
Sterile isotonic solution, such as saline solution, is provided to chamber 
13 from an external pressurized source, such as bag device 18 illustrated 
in FIG. 1, carried on a suitable standard 19 suitably adjusted to provide 
a controlled pressure delivery (conventionally at approximately 300 
millimeters of mercury) of the solution therefrom through a conduit 20 
connected to the bag device 18 by a conventional connector 21. The sterile 
solution is delivered from the pressure chamber 13 through a connector 
generally designated 22, which, in the illustrated embodiment, comprises a 
stopcock, selectively connecting the pressure chamber to a Luer connector 
23, or a bypass connector 24, as a result of suitable manipulation of a 
handle 25. 
Pressure transducer 16 provides an electrical output signal corresponding 
to the pressure of fluid in pressure chamber 13, which is transmitted to 
an external monitor 26 of conventional construction through a cable 27 
terminating in a connector 28. Connector 28 is adapted to have readily 
separable connection to a connector 29 connected to monitor 26 through a 
cable 30. Flow of saline solution from connector 23 is effected through a 
connector 31 at the distal end of a conduit 32 terminating in a catheter 
33 providing an invasive connection to the patient when inserted into a 
blood vessel of a patient. 
Thus, the boundaries of the device 11 are defined by the connectors 21, 28 
and 23 so that the device may be provided as an integral assembly readily 
connected into the system wherein the external components comprise the 
saline source bag device 18, the monitoring apparatus 26, and the 
connection 31 to the conduit connected to the patient. 
As further illustrated in FIG. 1, flow control valve 14 is provided with an 
outer connector 34 engaged by an angle operator 35 which, when depressed, 
pulls the valve to an open position, permitting a high rate of flow of the 
saline solution from source 18 into pressure chamber 13. As best seen in 
FIG. 2, operator 35 includes an apertured end portion 36 extending between 
the connector 34 and a cap 37 on housing 12 sealing the end of the 
pressure chamber inlet portion 44. A finger engageable portion 38 extends 
angularly to portion 36 and is received in a space 39 so that when the 
portion 38 is urged inwardly toward housing 12, portion 36 is rocked 
outwardly to urge connector 34 outwardly and thereby pull the valve 14 to 
an open position. 
More specifically, valve 14 is generally similar to and functions generally 
similar to the fast flush valve of the above discussed U.S. Pat. No. 
4,291,702, which patent is incorporated by reference herein. Briefly, 
however, valve 14 is defined by a valve body 40 having a through bore 
receiving a cylindrical insert 41 provided with a capillary bore 42 
illustratively having a diameter of approximately 0.002 inches. At its 
outer end, the insert is provided with radially opening passages 43 for 
conducting saline solution from inlet portion 44 of pressure chamber 13 
into insert 41 for metered flow outwardly through capillary bore 42 into 
pressure chamber 13. 
As further illustrated in FIG. 3, connector 34 is provided with a stem 45 
bonded to the outer end 46 of insert 41, so that when connector 34 is 
urged outwardly by operator 35, as discussed above, insert 41 and body 40 
are pulled outwardly to disengage the body from an annular O-ring seal 47 
and thereby provide a flow path from inlet portion 44 around the seal to 
pressure chamber 13 and stopcock 22. The valve is biased to the closed 
position wherein body 40 seats against O-ring 47 which, in turn, is urged 
against a frustoconical shoulder 48 between inlet portion 44 and pressure 
chamber 13 by a resilient tube 49 extending axially between valve body 40 
and cap 37. As shown in FIG. 3, the length of tube 49 is slightly greater 
than the space between body 40 and cap 37 so that the tube is under 
compression, thereby providing the desired biasing of the valve to the 
closed disposition illustrated in FIG. 3 and sealing of the cap to the 
valve body 40 about the stem 45. 
As further shown in FIG. 3, supply conduit 20 is connected to pressure 
chamber inlet portion 44 through a passage 50 opening to portion 44 
adjacent O-ring 47. 
The resiliency of tube 49 is preselected to permit outward movement of the 
valve body as a result of an increase in pressure in pressure chamber 13 
to an undesirably high pressure so as to relieve the pressure by directing 
the isotonic saline solution to the bag 18 and thereby to prevent damage 
to the transducer from such high pressure conditions or surges. 
As indicated briefly above, the invention comprehends the provision in 
housing 12 in combination with the flow control valve 14 of the pressure 
transducer 16, permitting the pressure transducer to be included with the 
other components of the device for throwaway use of the entire system by 
virtue of the low cost construction thereof. In the illustrated 
embodiment, as shown in FIGS. 6-9, the pressure transducer includes a 
deflectible beam 51 having one end 52 secured to a strain isolator 53 as 
by electrostatic bonding 54, or suitable adhesive means. Beam end 52 is 
provided with a wheatstone bridge strain gage 55. In the illustrated 
embodiment, the strain gage resistance grid is fused into the beam which, 
illustratively, may be formed of a suitable deflectible material, such as 
silicon, etc. The beam preferably has a wafer thickness of approximately 
0.01 inches for facilitated manufacture and defines the major restraint 
component of the pressure transducer. 
As further indicated in FIG. 9, the strain gage bridge includes a plurality 
of pads 56 to which fine gold alloy wires 57 are electrically connected at 
one end. As shown in FIG. 7, the opposite end of wires 57 are electrically 
connected to flat conductors 58 of cable 27 received in a flexible conduit 
59. 
As illustrated in FIG. 2, the distal end of cable 27 is received in a 
connector head 60 and connected to a connector plate 61 thereof through 
calibrating resistors 62. The calibrating resistors are calibrated by 
laser trimming in a conventional manner so as to calibrate the pressure 
transducer accurately for clinical use. As further shown in FIG. 2, the 
head 60 defines a distal socket portion 63 for receiving the male 
connector 29 (see FIG. 4). The male connector houses the end of a cable 64 
for providing connection from connector plate 61 to the monitor apparatus 
26, as illustrated in FIG. 4. As indicated above, the male connector 29 
and cable 30 are reusable components of the overall system, being 
separable from connector 28 for disposal of the device 11 as a whole. 
In the illustrated embodiment, connector plate 61 is provided with a 
plurality of connector pins 79 aligned with and adapted to be received in 
suitable female connectors 80 in a connector plate 81 in connector head 
29. 
The preferred embodiment of pressure transducer 16 is illustrated in FIG. 
29. As shown therein, the distal end 65 of beam 51 is connected to a 
projecting pin portion 66 of a small diameter link 67 having its opposite 
end 68 connected to the midportion 69 of a diaphragm 70. Diaphragm 70 is 
bonded to an annular rib 71 on housing wall 72 separating pressure chamber 
13 from transducer chamber 15. 
A frame generally designated 73 extends coaxially oppositely of rib 71 from 
the opposite face of the diaphragm, and in the pressure transducer 74 
illustrated in FIG. 29 is defined by a pair of coaxial annular portions 75 
and 76. As shown, isolator 53 is mounted to the outer frame portion 76. 
Diaphragm 70 is formed of a compliant material so as to be highly flexible, 
and in the illustrated embodiment, comprises a disc of polycarbonate 
having a thickness of 0.002 inches. Frame portion 75, in the illustrated 
embodiment, comprises an annular element formed of molded polycarbonate 
and link 67 comprises a cylindrical element formed of molded 
polycarbonate. The link, diaphragm and frame portion may be molded as a 
one-piece force collector structure. Alternatively, the link, diaphragm 
and frame portion may be separately formed and secured together. Thus, the 
frame portion 75 may be secured to the diaphragm by a cyanoacrylate 
bonding agent, and the diaphragm may be sealed to the link by suitable 
polycarbonate solvent. The diaphragm, in turn, may be secured to the 
housing rib 71 by a suitable polycarbonate solvent. 
Isolator 53 may be secured to the beam end 52 by an epoxy adhesive. In the 
illustrated embodiment, frame portion 76 is formed of glass and beam end 
52 is bonded thereto with an epoxy adhesive. Frame portion 76 is bonded to 
frame portion 75, in turn, with an epoxy adhesive. As indicated above, the 
beam comprises a 0.01 inches thick wafer of a suitable relatively stiff 
material so as to provide a major restraint portion of the force 
transducer. 
Additional embodiments of pressure transducers within the scope of the 
invention are illustrated in FIGS. 10-28. Thus, as seen in FIG. 10, a 
pressure transducer generally designated 16a is shown to comprise a 
pressure transducer generally similar to transducer 16, but having a 
one-piece frame 73a formed entirely of molded polycarbonate resin. 
In FIG. 11, another form of pressure transducer embodying the invention is 
shown to comprise a pressure transducer 16b which is generally similar to 
pressure transducer 16a but wherein the link 67b includes a large diameter 
portion 68b connected to the diaphragm and a small diameter portion 78b 
connected to the pin 66b in turn connected to the beam 51b. The link 67b, 
however, is formed as a one-piece stepped element of polycarbonate resin. 
Referring now to FIG. 12, still another pressure transducer generally 
designated 16c embodying the invention is shown to comprise a structure 
generally similar to that of pressure transducer 16a except that the 
diaphragm 70c is bonded to the frame 73c, the housing wall 72c, and the 
link 67c by a cyanoacrylate bonding agent. 
A further modified form of pressure transducer 16d is illustrated in FIG. 
13 to comprise a pressure transducer similar to pressure transducer 16c 
except that the link 67d comprises a stepped link having a large diameter 
portion 68d and a reduced diameter portion 78d. 
Referring to the embodiment of FIG. 14, a pressure transducer generally 
designated 16e is shown to comprise a pressure transducer similar to 
pressure transducer 16c except that the diaphragm 70e is formed of 
polyurethane. 
The pressure transducer generally designated 16f of FIG. 15 is similar to 
pressure transducer 16e except that the link 67f is provided with a large 
diameter portion 68f and a small diameter portion 78f similar to the link 
67b of FIG. 11. 
Referring now to FIG. 16, a further modified form of pressure transducer 
designated 16g is shown to comprise a pressure transducer generally 
similar to transducer 16c but wherein the isolator comprises a washerlike 
ring 53g. In the illustrated embodiment, the ring is formed of Invar metal 
and has a thickness of approximately 0.02 inches. The beam 51g is bonded 
to the Invar ring by suitable material, such as epoxy adhesive. 
A pressure transducer generally designated 16h is illustrated in FIG. 17 
and comprises a pressure transducer generally similar to pressure 
transducer 16g but wherein the link includes a small diameter portion 78h 
and a large diameter portion 68h solvent bonded to the diaphragm 70h. 
Referring now to FIG. 18, still another form of pressure transducer 
generally designated 16i embodying the invention is shown to comprise a 
pressure transducer similar to pressure transducer 16g but wherein the 
diaphragm 70i is formed of silicone rubber and has a thickness of 
approximately 0.005 inches. The diaphragm is bonded to the link 67i by 
suitable epoxy resin. 
In FIG. 19, still another form of pressure transducer generally designated 
16j is shown to comprise a pressure transducer generally similar to 
pressure transducer 16i but wherein the link includes a small diameter 
portion 78j and a large diameter portion 68j bonded to the diaphragm by a 
suitable epoxy resin. 
Referring now to the embodiment of FIG. 20, a pressure transducer generally 
designated 16k is shown to comprise a pressure transducer generally 
similar to transducer 16b but wherein the housing 12k defines a cap 
wherein the diaphragm 70k is spaced therefrom, and the frame 73k is 
solvent-bonded to the cap. 
A pressure transducer generally designated 16u is illustrated in FIG. 21 to 
comprise a pressure transducer similar to transducer 16k but wherein the 
housing 12u defines an edge mounting of the pressure transducer. 
In FIG. 22, a pressure transducer generally designated 16m is shown to 
comprise a pressure transducer generally similar to pressure transducer 
16b but wherein the pin portion 66m of the link 67m has a reduced diameter 
so as to have increased flexibility. 
Still another form of pressure transducer generally designated 16n is 
illustrated in FIG. 23 to comprise a pressure transducer wherein the 
diaphragm is omitted and replaced by a piston 70n reciprocably movable in 
a tubular gel seal 82n self-bonded to the frame 73n. The frame is solvent 
bonded to the housing 12n. 
As illustrated in FIG. 23, the piston may be configured to be relatively 
rigid. As will be obvious to those skilled in the art, alternatively the 
piston may have a thinner configuration to provide greater flexibility 
therein. 
Referring to the embodiment of FIG. 24, a pressure transducer generally 
designated 16p is shown to comprise a pressure transducer which is similar 
to transducer 16k but wherein the frame includes an outer portion 83p 
formed of glass, permitting the elimination of the isolator by the epoxy 
bonding of the beam 51p to the outer end of the glass frame portion 83p. 
Further, as shown in FIG. 24, the link generally designated 67p includes a 
small diameter, intermediate pin portion 66p connected to the diaphragm 
70p by a retainer 84p and to the beam by a retainer 85p. The pin portion 
66p is preferably formed of glass and the retainers, in the illustrated 
embodiment, are formed of polycarbonate resin. 
A further modified form of pressure transducer generally designated 16q is 
illustrated in FIG. 25. As shown therein, the pressure transducer is 
similar to pressure transducer 16p but includes an intermediate frame 
portion 86q and an outer frame portion 83q disposed in series with the 
inner frame portion 87q. In the embodiment of FIG. 25, the frame portions 
are formed of polycarbonate and are bonded together by a suitable epoxy 
resin. The link pin generally designated 67q includes an inner portion 
84q, an intermediate portion 91q, and an outer portion 83q, each of which 
is formed of molded polycarbonate resin, the link portions being bonded 
together by a suitable epoxy resin adhesive. As shown in FIG. 25, the 
inner link portion 84q may be provided with a reduced diameter connecting 
portion 89q received in a recess 90q of the intermediate link portion 88q. 
Referring now to the embodiment of FIG. 26, a pressure transducer generally 
designated 16r is shown to comprise a pressure transducer generally 
similar to transducer 16a but wherein the frame 73r is formed of ground 
glass in a suitable binder. 
Still another form of pressure transducer generally designated 16s is 
illustrated in FIG. 27 to comprise a pressure transducer generally similar 
to pressurc transducer 16r but wherein the frame generally designated 73s 
includes an inner portion 87s and an outer portion 83s. In the illustrated 
embodiment, frame portion 87s is formed of polycarbonate resin and frame 
portion 83s is formed of ground glass in a suitable binder, the frame 
portions being bonded together by a suitable epoxy resin adhesive. As 
further shown in FIG. 27, the link generally designated 67s includes an 
inner portion 84s bonded to the diaphragm 70s and an outer portion 91s 
interconnected by a small diameter portion 89s on link portion 84s 
received in a recess 90s in link portion 91s. 
Still another form of pressure transducer generally designated 16t is 
illustrated in FIG. 28 to comprise a pressure transducer generally similar 
to pressure transducer 16a but wherein the diaphragm 70t is solvent-bonded 
to the frame 73t, as well as to the housing 12t. Alternatively, the 
diaphragm 70t may be bonded to the frame 73t by a cyanoacrylate adhesive 
within the scope of the invention. 
Each of the additional embodiments of the invention as disclosed in FIGS. 
10-28 as discussed above, is similar to the preferred embodiment pressure 
transducer 16 shown in FIG. 29 except for the differences discussed above. 
Broadly, the different embodiments utilized different configurations of 
the frame and link and different methods of effecting the bonding together 
of the elements of the pressure transducer. However, each of the 
embodiments is similar in providing a pressure-responsive movable element 
acting on the distal end of a cantilevered beam which is mounted in 
substantially spaced relationship to the movable element so as to have 
high electrical resistance therebetween. The movable element is connected 
to the beam by a link structure which may have any one of the large number 
of different forms illustrated in the different embodiments discussed 
above. 
In each of the embodiments, the beam is mounted in association with the 
housing by an isolator means which, in certain embodiments, comprises a 
separate element, and in other embodiments, comprises a portion of the 
frame secured directly or indirectly to the housing. 
The invention comprehends that, in certain of the embodiments, the frame 
diaphragm and link be formed integrally as a one-piece molded element of a 
suitable synthetic resin, such as polycarbonate resin. Alternatively, as 
discussed above, the invention comprehends forming the elements of the 
force collector separately and effecting a bonded connection therebetween 
either by fusion bonding or by adhesion bonds, such as by an epoxy resin 
adhesive. 
Each of the different forms of pressure transducer lends itself to 
economical manufacture by mass production. Further, the electrical 
connections to the strain gage bridge may be readily effected by means of 
the flat conductor cable 27 being brought into the pressure transducer 
chamber 15 through the housing in the conduit 59, with the connection 
between the cable and the strain gage bridge being effected by the fine 
wires 57, as illustrated in FIG. 3. 
The invention comprehends that the elasticity in the strain gage be 
provided primarily by the beam rather than by the diaphragm or piston. In 
the ilustrated embodiment, the beam comprises a single crystal deflecting 
member, such as a silicon wafer member. The strain gage bridge may be 
diffused into the silicon wafer surface and calibration of the system may 
be readily effected as discussed above by trimming of the external 
resistors 62 for further effectively minimizing cost of manufacture. 
By utilizing different materials in the link, as shown in a number of the 
embodiments, automatic temperature compensation may be provided, further 
effectively minimizing the cost of the system. 
By utilizing the improved flow control valve 14, a pressure relief to the 
pressure chamber 13 is provided, thereby further permitting effective 
minimization of cost of the pressure transducer by eliminating the need 
for high pressure protective means. More specifically, whenever a high 
pressure condition exists in the pressure chamber, the pressure will be 
relieved outwardly through the valve which may move from engagement with 
O-ring 47 against the resilience of the tubular resilient member 49 so 
that high pressure surges will be relieved to the sterile solution supply 
bag, avoiding damage to the pressure transducer. 
The use of a synthetic resin, such as polycarbonate plastic, for a major 
portion of the components of the system provides a low cost, mass 
producible structure. 
As discussed, as a result of the several above discussed features providing 
low cost of manufacture of the system, the cost thereof is effectively 
maintained at a sufficiently low level as to effectively permit the device 
to be considered as a throwaway, one-time use physiological pressure 
sensing system. Thus, the invention solves a serious problem in clinical 
pressure sensing operations of possible cross-contamination and infection 
by completely eliminating the need for the reuse of any of the system 
components by transfer from one patient to another. As discussed above, 
the elimination of the need for cleaning and resterilization of any of the 
components effectively improves the reliability of the system, solving 
another vexatious problem in such clinical pressure sensing operations. 
In use, the pressure sensing system 10 is set up, as illustrated in FIG. 1, 
with the device 11 interconnected between the source of sterile solution, 
the output monitoring device, and the patient. As shown in FIG. 1, the 
connector 21 provides a ready connection to the source of sterile solution 
18. The connector 28 provides means for readily connecting the device to 
the monitor connector 29, and the connector 22 provides means for readily 
connecting the device to the catheter 33 through the connector 31. 
The stopcock connector 22 permits the taking of blood samples by the 
suitable selective positioning of the handle 25 so as to discharge blood 
from the patient through the connector 24. The stopcock is arranged so as 
to close all connections, when desired. 
As discussed above, the fast flush valve is readily manually operable by 
the simple depression of the finger actuated portion 38 of operator 35. 
Thus, the initial filling of the system with sterile solution may be 
effected by opening of the valve 14 by the depression of handle portion 
38. As discussed above, in the closed position of the valve, a small flow 
passage is maintained through the ports 43 and capillary bore 42 so as to 
continuously provide a flow of sterile saline solution through the system 
and catheter so as to maintain the catheter unclogged as by the patient's 
blood constituents. 
The device may be maintained connected to the patient notwithstanding the 
application of high potentials to the patient, such as defibrillation 
potentials as the pressure transducer sensing strain gage is electrically 
isolated from the fluid in the pressure chamber. As indicated above, the 
electrical isolation further prevents injury to the patient as from 
electrical potentials appearing on the sensor beam as from electrical 
failure of the output elements, such as monitor 26. 
As the cost of the device 11 is relatively low, upon completion of the use 
thereof with a given patient, the entire device, up to and including the 
connectors 21, 28 and 22, as well as the patient line, may be discarded so 
as to effectively eliminate any possibility of cross-contamination with 
other patients. Such low cost is effected in device 11 while yet providing 
high accuracy which is necessary for accurate clinical determinations. 
The foregoing disclosure of specific embodiments is illustrative of the 
broad inventive concepts comprehended by the invention.