Isolation system for pressure gauges for permitting repeated use without sterilization

Systems and methods for isolating a pressure gauge from sources of potential contamination so that the pressure gauge may be reused in multiple medical procedures without having to be subjected to a sterilization procedure. The systems of the invention may include a syringe assembly having a pressure gauge removably attached to a syringe. The pressure gauge is isolated from sources of potential contamination in at least two ways. First, a flexible membrane separates a pressure transducer diaphragm of the pressure gauge from the pressurized fluid of the syringe. The flexible membrane prevents the pressure gauge from contacting the fluid and transmits pressure and forces from the fluid to the pressure gauge. Second, a substantially transparent disposable bag or film covers surfaces of the pressure gauge that would be otherwise exposed to human contact or other contaminants. During medical procedures, the pressure gauge maintains its sterile condition. After use, the pressure gauge may be removed from the syringe and subsequently used with a second syringe without an intervening sterilization procedure. The syringe assemblies may further include a balloon-tipped catheter for use in angioplasty and related medical procedures.

BACKGROUND OF THE INVENTION 
1. The Field of the Invention 
The present invention relates to pressure gauges for monitoring fluid 
pressure generated in a syringe during a medical procedure such as 
angioplasty. More particularly, the present invention relates pressure 
gauges that are isolated from potential sources of contamination so as to 
be repeatedly used in medical procedures without being sterilized between 
uses. 
2. Relevant Technology 
In recent years, balloon-tipped catheters have become increasingly useful 
in various medical procedures. For example, balloon-tipped catheters have 
been used to reduce the intrusiveness of medical procedures in various 
fields of medicine, such as urology, gynecology, cardiology, and the like. 
Particularly in the treatment of coronary artery disease, the use of 
balloon-tipped catheters and their associated fluid pressurization systems 
has become widespread. 
Coronary artery disease is the narrowing of the arteries that feed 
oxygen-rich blood to the heart. The heart needs adequate amounts of oxygen 
to continually and efficiently pump blood throughout the body. When 
arteries leading to the heart become narrowed and constricted due to 
coronary artery disease, several problems can develop. A person with 
coronary artery disease can experience angina, which is characterized by 
chest pain or pressure that radiates to the aim or jaw and is caused by a 
lack of oxygen-rich blood to the heart muscle. If untreated, coronary 
artery disease can lead to or contribute to heart failure and death. 
In recent years, coronary angioplasty has become a common and accepted 
alternative to the vastly more intrusive coronary bypass surgery. Coronary 
bypass surgery involves surgical access to the heart, placing the patient 
on an extracorporeal blood oxygenation system so that the heart can be 
stopped for surgery, and then surgically attaching one or more passageways 
by which blood can bypass a clogged coronary artery, all under general 
anesthesia. Coronary angioplasty, which can be performed using a local 
anesthetic, involves running a dilation or "balloon-type" catheter to the 
diseased artery and then inflating the balloon in order to compress plaque 
within the artery, thereby obtaining increased blood flow to the heart. 
Compared to coronary bypass surgery, coronary angioplasty is less 
intrusive and traumatic, typically involves less risk to the patient, and 
significantly reduces the patient's discomfort and recovery time. 
During inflation of the balloon during angioplasty, no blood can flow 
through the artery that is being mechanically dilated. The disruption of 
blood flow must be limited in duration to about 20 to 60 seconds, so as to 
avoid tissue damage due to oxygen deprivation. Hence, it is important to 
carefully monitor the inflation pressure and duration to ensure that blood 
flow is restored before tissue damage can occur. In most cases, it is not 
possible to adequately dilate a diseased artery in a single inflation. In 
cases where it is necessary to undertake multiple inflations in the same 
artery, it is important to allow sufficient time between successive 
inflations so that the tissues fed by the diseased artery can become fully 
oxygenated before blood flow is disrupted again. At the same time, a 
successful angioplasty procedure requires that the dilation of the artery 
be conducted for a significant period of time. 
Various devices and gauges have been developed for monitoring inflation and 
deflation of balloon tipped catheters during angioplasty. A typical 
pressure gauge of the prior art has a pressure transducer diaphragm that 
is in direct fluid contact with the inflation fluid within the inflation 
syringe. For example, the pressure gauge is directly mounted on the 
exterior of the syringe barrel over a port extending through the barrel. 
As fluid pressure is generated within the inflation syringe, the fluid 
pressure is transmitted through the port to the pressure transducer 
diaphragm. The pressure gauge senses the fluid pressure and displays or 
records the magnitude of the fluid pressure in analog or digital form. 
In order to maintain a sterile environment during the angioplasty 
procedure, several techniques have been developed with respect to pressure 
gauges and methods of sensing fluid pressure. It can be understood that as 
the pressure transducer diaphragm is exposed to inflation fluid, the 
pressure gauge is subject to possible contamination. Moreover, the exposed 
surfaces of the pressure gauge, such as the housing and a display window 
through which the measurement readings are displayed, may be exposed to 
other contaminants during use. For example, medical personnel sometimes 
touch the pressure gauge during normal use and fluids may be splashed onto 
pressure gauge surfaces. Although pressure gauges and the inflation fluid 
ordinarily do not contact the patient's tissue or bodily fluids, it is 
important that the pressure gauges be sterile for safety reasons. Using a 
pressure gauge that has previously been contaminated by inflation fluid or 
contact with other contaminants without subjecting it to a sterilization 
procedure has been unacceptable according to current medical practice. 
One method for providing sterile pressure gauges is to use a new device for 
each angioplasty or other medical procedure. According to this method, the 
pressure gauges are one-use devices that are discarded after one medical 
procedure. Disposable pressure gauges ensure that each angioplasty is 
performed with a sterile pressure gauge. However, the use of disposable 
pressure gauges adds significant cost to each operation. 
Alternatively, other pressure gauges are designed to be sterilized after 
being used in a medical procedure, and are thereby reusable. For example, 
sterilization may be conducted thermally in an autoclave or chemically by 
applying a sterilizing chemistry to the pressure gauge. Typically, such 
sterilizable pressure gauges have surfaces of stainless steel or another 
sterilizable material. Examples of sterilizable and reusable pressure 
gauges are disclosed in copending U.S. patent application Ser. No. 
09/048,091, filed Mar. 25, 1998, entitled "Pressure Gauge with Digital 
Stepping Motor and Reusable Transfer Plug." For purposes of disclosure, 
the foregoing patent application is incorporated herein by specific 
reference. Sterilizable pressure gauges represent a significant 
advancement in the art, since the cost of a new pressure gauge is not 
included in each medical procedure. 
Either of the foregoing two methods are adequate for providing sterile 
pressure gauges in many situations. However, it can be understood that it 
would be a fixer advancement in the art to provide pressure gauges that 
are both reusable and do not need to be sterilized between uses. Pressure 
gauges that may be used multiple times without intervening sterilization 
procedures would significantly reduce the cost and effort now required for 
providing sterile pressure gauges. In particular, the cost associated with 
the time and equipment for sterilizing reusable pressure gauges could be 
avoided. In addition, such pressure gauges would eliminate the cost of 
using a new, one-use pressure gauge for each medical procedure. 
SUMMARY OF THE INVENTION 
The present invention relates to pressure gauges that are reusable in 
multiple medical procedures and that do not need to be sterilized between 
uses. The pressure gauges are configured for use with inflation syringes 
in a wide range of medical procedures, including angioplasty and related 
operations. To ensure that the pressure gauges of the invention are 
sterile during the multiple medical procedures, the pressure gauges are 
isolated from the environment and potential contaminants in at least two 
ways. First, a flexible membrane disposed between the inflation fluid and 
the pressure gauge isolates the pressure transducer diaphragm from direct 
contact with the inflation fluid in the syringe. Second, a transparent 
plastic bag or film covers the surfaces that would be otherwise exposed in 
order to prevent medical personnel or other sources of contamination from 
contacting the pressure gauge. 
In one implementation of the invention, the pressure gauge is included in a 
syringe assembly. The pressure gauge is mounted on the barrel of an 
inflation syringe to detect the pressure generated by inflation fluid 
within the syringe. A catheter, which may be balloon-tipped, is in fluid 
communication with the inflation fluid by being attached to the distal end 
of the inflation syringe. The inflation syringe has a plunger slidably 
disposed within the syringe barrel. Advancement of the plunger through the 
barrel forces inflation fluid from the barrel into the catheter. When the 
syringe is used in combination with a balloon-tipped catheter, the 
inflation fluid forced into the catheter causes inflation of the balloon 
and a corresponding increase in fluid pressure. 
In this implementation, a port extends through the sidewall of the barrel 
and permits fluid communication between the syringe and a pressure chamber 
disposed on the outer surface of the barrel. The pressure chamber is 
enclosed by a flexible membrane bonded to the outer surface of the barrel 
over the port. The pressure gauge is rigidly and removably attached to the 
outer surface of the syringe barrel such that a pressure transducer 
diaphragm of the pressure gauge is in direct contact with the flexible 
membrane. As pressure is generated within the syringe, the pressure is 
communicated through the port and to the pressure chamber. Since the 
flexible membrane is in contact with the pressure gauge, force associated 
with the generated fluid pressure is transmitted through the membrane to 
the pressure transducer diaphragm. In this manner, the pressure gauge 
senses and detects the fluid pressure within the syringe without being in 
direct fluid contact with the inflation fluid. Moreover, the flexible 
membrane isolates the pressure gauge from the inflation fluid, thereby 
preventing the inflation fluid from contaminating the pressure gauge. 
According to one aspect of the present invention, an O-ring circumscribes 
the port and is disposed between the outer surface of the barrel and the 
flexible membrane. The O-ring facilitates the transmission of force from 
the pressurized fluid in the pressure chamber to the pressure gauge. In 
particular, the O-ring supports the flexible membrane and prevents it from 
collapsing against the outer surface of the barrel. This configuration 
maintains the patency of the pressure chamber and provides adequate 
contact between the pressure gauge and the flexible membrane, even if 
vacuum pressure is experienced. 
According to this implementation, a disposable transparent film or bag 
covers surfaces of the pressure gauge that would otherwise be exposed. For 
example, the film may be a polypropylene bag having an elastic opening to 
securely stretch over and remain positioned on the pressure gauge. The 
film prevents potential contamination of the surfaces of the pressure 
gauge. For example, medical personnel may touch and handle the pressure 
gauge through the film without contaminating the pressure gauge surfaces. 
A pressure gauge of the invention may be used in multiple medical 
procedures by first removably attaching it to an inflation syringe 
according to the configuration described above. Next, the film or bag is 
applied to the pressure gauge to cover the otherwise exposed surfaces. The 
medical operation proceeds as usual, while the pressure gauge is used to 
monitor the fluid pressure generated in the inflation syringe. While the 
pressure gauge is attached to the inflation syringe, the flexible membrane 
isolates the pressure gauge from direct contact with the inflation fluid. 
Moreover, the film or bag prevents contamination of the surfaces of the 
pressure gauge. 
After the medical procedure is completed, the pressure gauge is removed 
from the inflation syringe, and the film and the inflation syringe may be 
discarded. The pressure gauge remains in the same sterile condition as 
before the medical procedure. As desired, the pressure gauge may again be 
removably attached to a new inflation syringe and used in another medical 
procedure. A significant advantage of the pressure gauges and the methods 
of the invention is that the pressure gauge does not need to be subjected 
to a sterilization procedure between uses, but instead maintains a 
medically-acceptable level of sterilization during repeated uses. 
These and other objects, features, and advantages of the present invention 
will become more fully apparent from the following description and 
appended claims, or may be learned by the practice of the invention as set 
forth hereinafter.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The present invention relates to pressure gauges that are reusable in 
multiple medical procedures and that do not need to be sterilized between 
uses. The invention further extends to syringe assemblies wherein a 
pressure gauge is removably attached to a syringe and is isolated from 
potential sources of contamination such as fluid within the syringe and 
contact with medical personnel or other contaminates. 
The pressure gauges are configured for use with syringes in a wide range of 
medical procedures, including angioplasty and related operations. To 
ensure that the pressure gauges of the invention are sterile during the 
multiple medical procedures, the pressure gauges are isolated from the 
environment and potential contaminants in at least two ways. First, the 
pressure transducer diaphragm is isolated from direct contact with the 
fluid in the syringe by a flexible membrane disposed between the fluid and 
the pressure gauge. Second, a disposable covering, such as a transparent 
plastic bag or film, covers surfaces that would be otherwise exposed in 
order to prevent medical personnel or other sources of contamination from 
contacting the pressure gauge. 
The invention may be best understood by referring to FIGS. 1-5, which 
illustrate the elements, features, and operation of one embodiment of the 
invention. In the embodiment that is primarily discussed herein, the 
syringe assembly is configured for use in angioplasty or other medical 
procedures in which the syringe is used to supply inflation pressure to a 
dilation catheter. While this is one presently preferred embodiment, it is 
to be understood that the broad principles taught herein may be applied to 
other medical devices that generate or experience fluid pressure. 
Furthermore, the invention is applicable to many types of medical 
procedures in which it is desirable to monitor fluid pressure using a 
pressure gauge in a sterile condition. Accordingly, the present invention 
is should not be limited to the specific embodiments disclosed in detail 
herein. 
Referring first to FIG. 1, one presently preferred embodiment of a syringe 
assembly is illustrated. Syringe assembly 10 includes a syringe 12, 
pressure gauge 14, and a catheter assembly 16, and is configured to be 
used in angioplasty or other related procedures. Syringe 12 includes a 
hollow barrel 18 and a plunger 20 slidably disposed within the barrel. A 
plug 22 is positioned at the distal end of plunger 20 to sealingly engage 
barrel 18 as the plunger is advanced and retracted through the barrel. A 
handle 24 of any convenient shape is located at the proximal end of 
plunger 20. A physician grasps handle 24 and advances plunger 20 through 
barrel 18, thereby expelling fluid from the barrel into catheter assembly 
16. 
In this embodiment, catheter assembly 16 is in fluid communication with 
syringe 12 by means of an opening 26 at the distal end of barrel 18. A 
balloon 28 may be positioned at the distal end of the catheter assembly 16 
for use in angioplasty or other related medical procedures. As fluid is 
expelled from syringe 12 into catheter assembly 16, the pressure of the 
fluid generally increases and balloon 28 inflates. When used in 
angioplasty, the inflated balloon 28 may be used to radially compress 
plaque deposits within diseased arteries. Pressure gauge 14 visually 
displays the magnitude of the fluid pressure within syringe 12. As 
inflation of balloon 28 continues, the operating physician may monitor the 
generated fluid pressure by referring to pressure gauge 14. Thus, pressure 
gauge 14 is one example of pressure monitoring means for detecting fluid 
pressure generated within the barrel of the syringe. 
Syringes similar to the one illustrated in FIG. 1 are more particularly 
described in U.S. Pat. Nos. 5,449,344 to Taylor et al. and 5,135,488 to 
Foote et al., which are incorporated herein by reference for purposes of 
disclosure. However, it is to be understood that the nature and mechanical 
aspects of syringe 12 are not limited to those specific features 
illustrated in FIG. 1 or disclosed in the foregoing patents, and that a 
variety of different types of syringe designs could be utilized without 
departing from the spirit and scope of the present invention. Indeed, the 
pressure gauges disclosed herein may be adapted to measure fluid pressures 
generated within devices other than syringes. In these cases, the pressure 
gauge is adapted to be respond to another fluid system in which a fluid 
pressure may be generated. 
Pressure gauge 14 is isolated from the fluid within syringe 12 in order to 
maintain the sterile condition of the pressure gauge and to allow the 
pressure gauge to be used in multiple medial procedures without 
intervening sterilization. In general, the pressure gauges of the 
invention remain isolated from the fluid by a flexible membrane or bladder 
that transmits forces from the fluid to the pressure gauge. Such flexible 
membranes or bladders are examples of diaphragm means for communicating 
fluid pressure in the syringe to the pressure gauge and for isolating the 
pressure gauge from direct contact with the fluid. 
FIG. 2 further illustrates syringe assembly 10 of FIG. 1, including a 
flexible membrane for transmitting forces to the pressure gauge. Barrel 18 
has a sidewall 30 with a port 32 extending therethrough. In this 
embodiment of the invention, an O-ring 34 concentrically surrounds port 32 
and is disposed on the outer surface of sidewall 30. Although the 
invention may be practiced in the absence of O-ring 34, its presence 
provides several advantages that are discussed herein. O-ring 34 may be 
formed, for example, from any suitable, pliant polymeric material. 
A flexible membrane 36 (shown in cutaway in FIG. 2) is also positioned on 
the outer surface of sidewall 30 and covers port 32 and is one example of 
the diaphragm means. Flexible membrane 36 may be formed from any material 
that is sufficiently flexible to transmit forces from the fluid to the 
pressure gauge and tough enough to withstand tearing, bursting, or 
otherwise failing in response to the pressures and forces that the 
membrane experiences during use. For example, a presently preferred 
flexible membrane 36 comprises a film formed from a polyester material, 
such as Mylar. Flexible membrane 36 is preferably joined to the outer 
surface of sidewall 30 in a fluid-tight manner by, for example, an 
ultrasonic or another bonding technique at or near periphery 38 of the 
flexible membrane. Accordingly, the interface at which flexible membrane 
38 is bonded to the outer surface of sidewall 30 constitutes one example 
of sealing means for joining the flexible membrane and the syringe in a 
fluid-tight manner. 
The syringe assembly preferably includes attachment means for removably 
attaching the pressure gauge to the syringe assembly. Hooks 40 or other 
male components formed on sidewall 30 are one example of the attachment 
means. In general, the attachment means may be any structure for rigidly 
securing the pressure gauge to the syringe assembly so as to resist 
displacement of the pressure gauge away from the syringe assembly as force 
is transferred from the flexible membrane to the pressure gauge. 
Furthermore, the attachment means generally allows the pressure gauge to 
be removed from the syringe assembly after use so that the pressure gauge 
may be reused with another syringe assembly. Turning to FIG. 3, the manner 
in which hooks 40 secure the pressure gauge may be further understood. 
Pressure gauge 14 includes slots 42 that matingly engage hooks 40, thereby 
securing the pressure gauge to the syringe assembly. Alternatively, the 
attachment means may include female components such as grooves, slots, or 
the like, that mate with corresponding structures on the pressure gauge. 
In another embodiment, the attachment means may comprise a threaded well 
formed about periphery 38 of flexible membrane 36, and which mates with a 
corresponding threaded neck on the pressure gauge. 
As shown in FIG. 3, pressure gauge 14 includes a pressure transducer 44 
having a diaphragm 46. In order for pressure gauge 14 to reliably sense 
the generated fluid pressure, diaphragm 46 is situated in direct contact 
with flexible membrane 36. In one embodiment, flexible membrane 36 may be 
biased against diaphragm 46 when the pressure within syringe barrel 18 is 
neutral with respect to the atmospheric pressure. The resilient properties 
of O-ring 34 facilitate the biased contact of flexible membrane 36 against 
diaphragm 46 and maintain such contact through a wide range of fluid 
pressures. 
Pressure gauge 14 and other structures that correspond to the pressure 
monitoring means may be substantially any mechanical or electronic device 
that senses forces transmitted through flexible diaphragm 36 and displays 
and/or records the magnitude of the sensed fluid pressure. One example of 
a suitable pressure gauge is disclosed in U.S. patent application Ser. No. 
09/048,091, filed Mar. 25, 1998, entitled "Pressure Gauge with Digital 
Stepping Motor and Reusable Transfer Plug." However, since the surface of 
the pressure gauges are isolated from potential contaminants in the 
environment, it can be understood that the specific structure, elements, 
and method of operation of the pressure gauges used with the invention are 
not critical. Furthermore, while the components of some pressure gauges 
have been limited to those that are able to withstand thermal or chemical 
sterilization procedures, such limitations are not present with respect to 
the pressure gauges of the invention. Accordingly, the pressure 
transducers, the power supplies, the display devices, and the other 
components included in the pressure gauges used with the invention need 
not be selected according to considerations regarding their compatibility 
with high temperature or chemical environments. 
FIG. 3 and the enlarged view of FIG. 4 further illustrate the manner in 
which pressure and forces are communicated between barrel 18 and pressure 
transducer diaphragm 46. As discussed above, positive fluid pressure with 
respect to atmospheric pressure is generated when the plunger of the 
syringe assembly is advanced into barrel 18. Port 32, extending through 
sidewall 30, establishes fluid communication between barrel 18 and a 
pressure chamber 48 situated at the outer surface of sidewall 30. Fluid 
generally fills pressure chamber 48 such that the pressure generated 
within barrel 18 is substantially the same as the pressure within pressure 
chamber 48. Pressure chamber 48 is defined by the inner surface 39 of 
flexible membrane 38, the outer surface 31 of sidewall 30, and O-ring 34, 
as shown in FIG. 4. 
As further illustrated in FIG. 4, O-ring 34 may be seated in an annular 
groove 54 formed into sidewall 30. O-ring 34 establishes a first 
fluid-tight seal 56 between itself and sidewall 30 and further establishes 
a second fluid-tight seal 58 between itself and flexible membrane 36. 
Fluid-tight seals 56 and 58 substantially prevent pressurized fluid from 
escaping from pressure chamber 48 into the surroundings. In view of the 
foregoing, O-ring 34 constitutes a further example of sealing means for 
joining flexible membrane 38 and syringe 12 in a fluid-tight manner. 
Moreover, O-ring 34 and fluid-tight seals 56 and 58 relieve much of the 
stress that would otherwise bear on the bonded interface between flexible 
membrane 38 and the outer surface of sidewall 30. As a result, the 
inclusion of O-ring 34 allows the interface between flexible membrane 38 
and sidewall 30 to be smaller, the minimum strength of the bond at the 
interface to be less, and the diameter of the flexible membrane to be 
smaller than would otherwise be required. However, the invention may be 
practiced in the absence of O-ring 34, in which case the bond at the 
interface between flexible membrane 38 and the outer surface of sidewall 
30 should be sufficiently strong to prevent the fluid pressure from 
breaking the bond. 
As positive fluid pressure is generated within barrel 18 and pressure 
chamber 48, the fluid exerts force on flexible membrane 36, which responds 
by transmitting the force to pressure transducer diaphragm 46. Thus, when 
the fluid pressure increases, the force transmitted to pressure transducer 
diaphragm 46 likewise increases. In some situations, syringe assembly 12 
may be used to generate a negative fluid pressure relative to atmospheric 
pressure by, for example, retracting the plunger part way through barrel 
18. In this case, the negative pressure is communicated to pressure 
chamber 48. In response to the negative pressure, flexible membrane 36 
tends to deflect downward, thereby reducing the volume of pressure chamber 
48. O-ring 34 prevents flexible membrane 36 from fully collapsing inwardly 
and closing the pressure chamber 48 and tends to maintain the contact 
between the flexible membrane and diaphragm 46 during negative pressure 
conditions. Thus, this embodiment of the syringe assemblies of the 
invention allows pressure gauge 14 to detect negative pressures generated 
within the syringe. 
FIGS. 3 and 5 further illustrate disposable transparent bag 50 that covers 
the otherwise exposed surfaces 52 of pressure gauge 14. Bag 50 and other 
substantially transparent films represent examples of covering means for 
protecting the pressure gauge from contamination during use of the syringe 
assembly in a medical procedure. One preferred material for use in bag 50 
is polypropylene, although a variety of other polymeric materials are also 
suitable. Because of the substantially transparent nature of bag 50, 
pressure gauge 14 may be visually monitored by the operating physician or 
other medical personnel during medical procedures. A preferred embodiment 
of bag 50 has an elastic or other resilient opening 60 that tends to close 
in around the base of pressure gauge 14 when applied thereto. Accordingly, 
when bag 50 covers pressure gauge 14, the bag is reliably secured over the 
pressure gauge and substantially resists inadvertently falling off during 
use. It can also be understood that bag 50 is relatively very inexpensive 
such that the savings gained by reusing the pressure gauges of the 
invention in multiple medical procedures, while eliminating the need for 
intervening sterilization operations, far outweigh the cost of the bags. 
Methods for using the pressure gauges and syringe assemblies of the 
invention to perform multiple medical procedures may also be described by 
making reference to FIG. 3. In a first step, there is provided a pressure 
gauge 14 in a sterile condition sufficient for medical use. Pressure gauge 
14 is then removably and rigidly attached to syringe assembly 12 as 
described herein. The transparent bag 50 may be stretched over pressure 
gauge 14 before it is attached to syringe assembly 12 in order to allow 
the pressure gauge to be handled by medical personnel without directly 
contacting pressure gauge surfaces. Alternatively, bag 50 may be applied 
to pressure gauge 14 after the pressure gauge has been attached to syringe 
assembly 12. Depending on the particular pressure gauge 14, a zeroing 
operation may be conducted to initialize the pressure reading with respect 
to the particular syringe assembly 12. With pressure gauge 14 in its 
desired position on syringe assembly 12, the angioplasty or other medical 
procedure is then performed as desired. It is noted that pressure gauge 14 
responds from the standpoint of the operating physician in a substantially 
similar manner as pressure gauges attached to a syringe according to a 
conventional configuration. In particular, pressure gauge 14 responds to 
fluid pressure generated within syringe 12 and displays and/or records the 
magnitude of the fluid pressure. 
After the medical procedure has been completed, pressure gauge 14 is 
removed from syringe assembly 12. Pressure gauge 14 is withdrawn from bag 
50 and both syringe 12 and bag 50 may be discarded. During the medical 
procedure, bag 50 prevents potential contaminants from contacting surfaces 
52, while flexible membrane 36 isolates diaphragm 46 from the fluid of the 
syringe assembly. Accordingly, pressure gauge 14 has not been contaminated 
during the previous medical procedure and remains in the same sterile 
condition as before being used. In this sterile condition, pressure gauge 
14 may be reused in combination with a new syringe 12 and a new bag 50 in 
a subsequent medical procedure. Pressure gauges may be repeatedly used an 
indefinite number of times according to the systems and methods of the 
invention. 
The present invention may be embodied in other specific forms without 
departing from its spirit or essential characteristics. The described 
embodiments are to be considered in all respects only as illustrative and 
not restrictive. The scope of the invention is, therefore, indicated by 
the appended claims rather than by the foregoing description. All changes 
which come within the meaning and range of equivalency of the claims are 
to be embraced within their scope.