Abstract:
A urodynamic catheter incorporating at least one balloon adjacent a distal end thereof and associated with a pressure lumen extending to a proximal end to be placed external to the body of a patient and usable with a transducer housing including a pressure transducer and a mechanism for alternatively venting an air column defined by the assembled pressure lumen and transducer housing to the ambient environment and closing the air column and charging it with air while reducing volume of the air column. One embodiment includes two, separately-chargeable balloons and a bladder fill tube, another embodiment includes a single balloon and a fill tube, and yet another embodiment, suitable for use as a reference catheter to measure abdominal pressure, includes only a single balloon and omits the fill tube. A novel catheter architecture and assembly technique are also disclosed, as are methods of using the inventive catheter.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to balloon-type catheters and, more specifically, to urodynamic catheters and methods of fabrication and use thereof. 
     2. State of the Art 
     A significant percentage of urinary tract disorders, particularly among women, are problems of bladder storage, or incontinence, which may be defined for purposes herein as the inability of the body to control the discharge of urine. Incontinence may result in at least a social, if not hygienic, problem, and is of significant concern to those afflicted. 
     Types and prevalence of incontinence among ambulatory adult women include Genuine Stress Incontinence (GSI), detrusor instability (urge incontinence), mixed incontinence (stress and urge), and other incontinence (overflow, neurogenic). The prevalence of detrusor muscle instability and of mixed incontinence has been observed to increase with age of the patient sample. Adult men have, to a lesser degree, similar incontinence problems, which are often associated with the prostate gland. Males also have urine retention issues due to the prostate. 
     The International Continence Society has defined GSI as “the involuntary loss of urine occurring when, in the absence of a detrusor contraction, intravesical pressure exceeds maximum urethral pressure.” In other words, stress incontinence is the accidental loss of urine resulting from laughing, sneezing, coughing or even standing up; any such exertion causes abdominal pressure, as transmitted to the bladder and the urine contained therein, to exceed the resistance to flow generated by the urethra, and principally the urethral sphincter. GSI may be further categorized as hypermobility of the bladder neck and intrinsic sphincteric deficiency (ISD). 
     Hypermobility of the bladder neck, resulting from descent of the pelvic floor, may be attributed to weakened pelvic floor muscles and connective tissue. This phenomenon may be observed in combination with nerve damage to the external genitalia resulting from childbirth, but may occasionally be noted in younger women who have not borne children. In a normal position, the bladder is supported by the pelvic muscles, which prevent increases in abdominal pressure from exceeding urethral pressure. When the pelvic muscles are weakened or damaged, the bladder neck is abnormally displaced during abdominal stress and the urethral sphincter closure pressure becomes inadequate to maintain continence. Loss of urine due to hypermobility-related GSI typically occurs in a periodic manner and the volume of urine is somewhat proportional to the severity of the condition. 
     ISD is a severe form of stress incontinence which occurs due to an intrinsic deficiency of the urethral closure mechanism or due to a dysfunctional urethra wherein, in either instance, the bladder neck is open at rest. Severe ISD results in continuous leakage of urine, or leakage responsive to only minimal subject exertion. In ISD, the bladder neck may be fixed, or hypermobile. ISD occurs in a significant number of instances due to urethral scarring from past incontinence surgeries, but may result from other causes. Only a small number of patients exhibit stress incontinence attributable to ISD. 
     Urge incontinence is the involuntary loss of urine due to an uninhibited detrusor muscular contraction associated with a strong urge to void (detrusor instability, or DI). DI is of unknown origin, in contrast to involuntary bladder contractions attributable to a known neurological disorder, which is called detrusor hyperreflexia. Urge incontinence is frequently associated with identifiable trigger mechanisms, such as the sound or feel of running water, or during intercourse. Urine loss can be substantial, as detrusor contractions continue until the bladder is empty. An urgency to void urine responsive to abnormally low volumes during filling of the bladder during a study without other, objective evidence of detrusor overactivity is conventionally thought to be due to a hypersensitive detrusor, and is thus termed “sensory” urgency. 
     Mixed incontinence usually refers to a combination of GSI and DI. 
     A urodynamic evaluation is often employed to identify the type and magnitude of incontinence experienced by the patient, in combination with other information regarding the patient obtained from a physical examination and disclosed or documented history. Urodynamic evaluations involve measurements of the bladder pressure, generally in comparison with a reference abdominal pressure obtained by a rectal or vaginal probe, as well as measurements of urethral pressure in comparison to bladder pressure. GSI may be diagnosed during filling of the bladder, as is DI. The former is notable for a loss of urine in response to the aforementioned laughter, coughing or other “provocative” influence, while the latter is associated with involuntary, marked, periodic detrusor contractions initiating voiding. Hypermobility and ISD may be identified by the use of two different conventional diagnostic methods, the urethral pressure profile (UPP); and the valsalva leak point pressure study (VLPP study). The former procedure measures urethral pressure versus bladder pressure as a catheter is withdrawn from the bladder through the urethra. The latter procedure fills the bladder to one or more selected volumes, at which juncture the patient is requested to “bear down” slowly as if voiding to a point where leakage occurs past the catheter, or a selected bladder pressure differential over the baseline pressure is reached. 
     Urodynamic evaluations are employed to obtain quantitative data regarding the bladder. The aforementioned bladder filling study, or so-called “filling cystometry”, measures the relationship of bladder pressure to volume of contained fluid. Bladder capacity and compliancy (the ability of the bladder to accommodate increasing volumes) is measured, as is the desire to void from a subjective, urgency standpoint. Finally, detrusor stability, or the ability of that muscle group to remain relaxed during filling of the bladder, even under the aforementioned types of provocation, is quantified. 
     So-called “multi-channel” cystometry is employed to correct measured bladder pressure to obtain a true bladder pressure by subtracting abdominal pressure. Bladder pressure is measured through a sensing element or port at the distal end of a catheter inserted into the bladder through the urethra, while abdominal pressure is measured by a sensing element at the distal end of a catheter inserted into the rectum or vagina of the patient. The difference in the two readings, the magnitudes of which are quantified as units of cm H 2 O, is characterized as detrusor pressure. Monitoring the relationship between observed bladder pressure and abdominal pressure during filling of the bladder, including response to provocation, results in a cystometrogram documenting quantitative bladder function. 
     Various catheter designs have been employed in the art for urodynamic studies, which designs generally include a fill tube to introduce a volume of liquid into the bladder. There are three categories of catheters known to the inventors: catheters which convey bladder pressure to a transducer external to the bladder through a liquid-filled column (lumen) extending through the catheter; catheters which employ an electronic microtransducer proximate the distal ends thereof; and fiber optic transducer-tipped catheters. The two former catheter types are primarily employed in hospital urology studies and urogynecology, while the latter type is generally employed in urology and gynecology evaluations performed in a physician&#39;s office. 
     Existing urodynamic catheter technologies each suffer from disadvantages. For example, liquid-filled catheters require elimination of air bubbles from the liquid column extending from the entry port in the bladder to the external transducer, require hydrodynamic compensation and may be susceptible to hydrostatic influence if the external transducer and distal fill port of the catheter are not on the same horizontal plane. Electronic microtransducer- and fiber optic transducer-tipped catheters, on the other hand, are relatively expensive. In addition, fiber optic transducers require special optical/electronic interface modules. While some transducer-tipped catheters are designed for re-use, the relatively fragile transducer and catheter structures preclude the most rigorous and effective sterilization techniques and thus make confirmation of absolute sterility impossible. Due to the increasing incidence of sexually-transmitted diseases, most notably AIDS and its HIV precursor, such uncertainty is of obvious concern. Moreover, transducer-tipped catheters typically tap pressure along only a portion of the circumferential side wall of the catheter, and are thus susceptible to inaccurate and inconsistent readings during UPP procedures, as well as to missing anomalies in portions of the urethral side wall which are not traversed by a rotationally-displaced transducer during longitudinal withdrawal of the catheter through the urethra in the course of a UPP. 
     Thus, it would be beneficial to the art to provide a reliable, disposable, and robust yet easily manufactured catheter employing a transducer external to the patient&#39;s body which would not rely upon a liquid-filled column and which would provide an automatic “zero” or reference pressure and an accurate physiological pressure, both of which may easily be repeated as needed while the catheter remains inserted and the catheter and transducer remain assembled. It would also be desirable to provide a catheter design affording the capability for assessment of urethral sphincter function through measurement of urethral closure pressure circumferentially about the catheter as it is withdrawn from the bladder through the urethra during a UPP, so as to identify any anomalies in the urethral side wall regardless of circumferential location and to avoid false readings from such anomalies. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention comprises a disposable urodynamic catheter employing at least one thin-walled, circumferentially-extending balloon proximate the distal, or patient end thereof which communicates pressure external to the balloon proximally to a transducer external to the patient&#39;s body through a small-volume, closed air column. The catheter is inserted with the at least one balloon in a collapsed state, which is then charged after entry of the catheter into the patient&#39;s bladder, or vagina, or rectum during a multi-channel cystometry procedure. 
     The present invention includes at least one pressure lumen extending distally from a proximal end of an outer tubing and having an outlet terminating within the confines of a small-diameter balloon circumferentially surrounding the outer tubing at or near the distal end thereof. After insertion into the patient&#39;s body, the proximal end of the pressure lumen is connected by a disposable connector to a housing incorporating a transducer and the air column extending between the balloon and the transducer is subsequently closed and charged with a minuscule volume (for example, ˜15 μliters) of air. Charging may be effectuated by an air volume displacement within the closed air column to minimize dead space therein after closure thereof. In one embodiment of the invention, two balloons independently chargeable may be employed, one proximate the distal end of the catheter and the other separated by a distance (for example, ˜6 cm) proximally therefrom. 
     Architecture of the catheter also comprises a significant aspect of the invention. For example, the balloon is of small diameter (˜0.160 inch fully inflated) and length (˜0.200 inch) when inflated for enhanced coupling of urethral pressure and is extremely thin-walled, on the order of 0.0002-0.0010 inch, resulting in exceptional pliability so that wrinkles therein do not impose artifactual forces (pressures) for ideal fluid pressure transmission through the balloon membrane. Moreover, the balloon volume is heat-stabilized by using a heat-shrink material to enable shrinkage of the balloon to a fixed volume and attachment to the outer tubing by heat-shrink of the balloon end cuffs using a hot air stream, thus avoiding the need for separate heat-shrink tubing hoops or adhesives at the balloon ends and providing an extremely smooth transition between the outer tubing and balloon on the catheter exterior. A small I.D. (between about 0.005-0.008 inch) pressure lumen about eighteen to twenty-four inches long leading to the balloon provides a low internal volume relative to the balloon volume within the closed air column, ensuring acceptable frequency response and providing a relatively wide measurement range (between 0 and 250 cm H 2 O). 
     Overall, the catheter is of small size, such as 7 French, and construction thereof affords good flexibility for easy insertion and added patient comfort and safety. Use of pressure lumen tubing of a different, higher durometer in comparison to the outer tubing provides a soft outer jacket and a rounded catheter distal end in combination with more rigid, less kink-prone pressure lumen tubing inside the outer tubing to achieve precision, small-bore pressure lines with a lower risk of perforation due to stiffness and less tendency to “set” in position when curled in a packaging pouch during shipment and storage prior to use. Moreover, the pressure lumen tubing is not affixed to the outer tubing except at a balloon location at a distal end of the pressure lumen tubing and where the pressure lumen tubing exits the outer tubing, promoting a flexible catheter with lower kink risk and minimizing contribution of the pressure lumen tubing to overall catheter stiffness. Similarly, a fill tube extending from the proximal end of the outer tubing to proximate a port at the distal end thereof is only secured distally to the outer tubing in the vicinity of pressure lumen tubing affixation and more proximally at an exit point of the pressure lumen tubing from the outer tubing. The use of a thin-walled, somewhat translucent material for the outer tubing permits the desirable use of UV-light curable adhesives (see below) without leaving the interior lumen tubing visible. The luer-lock (or similar) type pressure connectors employed at the proximal end of the pressure lumen tubing provide a low dead space connection and do not produce significant counter-torque on the catheter when twisted on to couple to a mating connector of the transducer housing port due to the substantially ends-only affixation of the pressure lumen tubing to the outer tubing. Further, the relative isolation of the pressure lumen tubing and fill tubing from the outer tubing provides strain relief to the former when physical stress is applied to the catheter, as mechanical loading is substantially accommodated by the outer tubing. 
     A tapered, interference fit connection between the cooperative luer-lock connectors of the pressure lumens and those of the reusable transducer housings minimizes dead space in the air column between the transducer and balloon. A unique, plunger-type charging structure incorporated in the transducer housing closes the air column from the ambient environment as the plunger advances beyond the extent of a relief or vent channel in the side wall of a plunger bore, and reduces dead space in the air column and charges enough air into the balloon such that pressure can be measured across the balloon membrane. In one embodiment, a deformable mass such as, for example, resilient silicone employed at an end of the plunger is compressed in a bore end as the plunger is advanced in the plunger bore, consuming column volume and providing an airtight seal at the plunger end of a passage leading to a transducer access port and a connector port. In another embodiment, a solid-ended plunger using an o-ring is employed to charge a fixed volume of air into the column and seal the passage. The configuration of the charging mechanism affords the capability for repeated, accurate one-handed closure and charging of the air column without disconnection of the catheter from the transducer housing. 
     During fabrication of the catheter preliminary to attachment of the balloon or balloons to the exterior of the outer tubing of the catheter, the outer tubing is formed to be round at its distal tip, then side holes or apertures are punched at the location or locations of a balloon. Then, the bladder (vesicle) filling lumen tubing and the smaller pressure lumen tubing are fed into the primary tubing for fast, easy assembly. The filling lumen tubing is fed from the proximal end until reaching the distal tip of the outer tubing. The pressure lumen tubing (two, if a two-balloon pressure sensing embodiment) is fed proximally from the punched aperture or apertures in the outer tubing side wall at the outer catheter tubing distal end and guided to exit the outer tubing through a slit in the primary tubing side wall along the proximal portion of the outer tubing. A measured volume of a UV-light curable (or alternatively an RTV) adhesive is then injected into the outer tubing bore into the side wall entry point around each pressure lumen tubing to secure the pressure lumen tubing and isolate the pressure lumen (and thus, eventually, the associated balloon) from the outer tubing bore. The adhesive is then UV-cured to secure the filling lumen tubing and pressure lumen tubing, the distal ends of the pressure lumen tubing are trimmed substantially flush with the exterior of the outer tubing, and the interior lumen tubing secured to the primary tubing in the vicinity of the slit using a collar or sleeve of heat-shrink material. 
     The present invention also encompasses a method of use of the catheter according to the invention, including measurement of bladder as well as, optionally, abdominal pressure using deformation of an air-filled balloon responsive to pressure on the exterior thereof to transmit pressure to a transducer external to the patient. In addition, the method of the present invention may include measurement of urethral pressure, such as, for example, during a UPP procedure, throughout an entire circumference of the catheter as it is withdrawn from the urethra. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
     FIGS. 1A and 1B respectively depict a side elevation of a first embodiment of a catheter according to the invention incorporating two balloons and a fill tube, and an enlarged, partial sectional side elevation of a distal end thereof; 
     FIGS. 2A and 2B respectively depict a side elevation of a second embodiment of a catheter according to the invention incorporating a single balloon and a fill tube, and an enlarged, partial sectional side elevation of a distal end thereof; 
     FIGS. 3A and 3B respectively depict a side elevation of a third embodiment of a catheter according to the invention incorporating a single balloon, and an enlarged, partial sectional side elevation of a distal end thereof; 
     FIGS. 4A and 4B respectively depict enlarged sectional elevations of a portion of the catheter of the first embodiment, FIG. 4A showing the balloons in an uncharged state and FIG. 4B showing the balloons in a charged state; 
     FIGS. 5A,  5 B,  5 C,  5 D and  5 E respectively depict a rear-quarter perspective view, a front-quarter perspective view, a side view, and a rear view of the transducer housing of the present invention and a side sectional view taken across line  5 - 5  in FIG. 5D with pressure lumen connected, the air column defined by the transducer and pressure lumen assembly being in the vented, or zero, position; 
     FIGS. 6A,  6 B,  6 C,  6 D and  6 E respectively depict a rear-quarter perspective view, a front-quarter perspective view, a side view, and a rear view of the transducer housing of the present invention and a side sectional view taken across line  6 — 6  in FIG. 6D with pressure lumen connected, the air column defined by the transducer and pressure lumen being in the charged, or run, position; 
     FIGS. 7A and 7B respectively depict an enlarged view of a first embodiment of a plunger assembly for the transducer housing as shown in FIGS. 5E and 6E in retracted and extended positions; 
     FIGS. 8A and 8B respectively depict an enlarged view of a second embodiment of a plunger assembly suitable for use in the transducer assembly of FIGS. 5A-E and  6 A-E; and 
     FIG. 9 is a view in partial anatomical cutaway illustrating the insertion of an embodiment of the urodynamic catheter of the present invention in the bladder of a patient and a second, reference abdominal catheter in the patient&#39;s vagina. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In the following description, the same reference numerals are employed to identify the same elements or features in various drawing figures for clarity. 
     Applicants hereby incorporate the disclosures of each of the following United States Patents in their entireties by this reference: Bobo, Sr., U.S. Pat. No. 5,573,007; Wallace et al., U.S. Pat. No. 5,951,497; and Wallace et al., U.S. Pat. No. 5,984,879. 
     Referring to FIGS. 1A and 1B in a first catheter embodiment 10 of the present invention, outer tubing  12  surrounds a fill tubing  14  extending substantially from rounded, distal end  16  of catheter  10  to proximal end  18  thereof. First and second pressure lumen tubing  20   a  and  20   b  respectively extend from distal and proximal balloons  22   a  and  22   b , which are preferably of substantially the same size, to male luer lock connectors  24   a  and  24   b . Balloon fill ports  26   a  and  26   b  at the distal ends of pressure tubing  20   a  and  20   b  open to the interiors  28   a  and  28   b  of balloons  22   a  and  22   b . The distal ends of pressure tubing  20   a  and  20   b  are secured within, and balloon fill ports  26   a  and  26   b  isolated from, the bore  30  of outer tubing  12  using a mass of UV-curable adhesive  32  injected into bore  30  through the side wall  34  of outer tubing  12  adjacent the fill port locations (see FIGS. 4A and 4B for enlarged views). Pressure lumen tubing  20   a  and  20   b  may exit outer tubing  12  through a slit in the side wall  34  thereof, at which location a protective heat shrink collar or sleeve  35  is employed to secure pressure lumen tubing  20   a  and  20   b  and fill tubing  14  and prevent kinking thereof. Fill tubing  14  extends from its distal end near fill port  40  in the side wall  34  of outer tubing  12  proximally through outer tubing  12  to a female connector  36 , which may comprise a luer lock or other suitable connector and which preferably has associated therewith a plug element or cap (shown)  38  for closure thereof. Fill tubing  14  is thus sealed inside of the outer tubing  12 , which physically supports the fill tubing  14  and prevents it from kinking. 
     Referring to FIGS. 2A and 2B, a second catheter embodiment  100  of the present invention is depicted. Catheter  100  is similar to catheter  10 , but includes only a single balloon  22  and associated pressure lumen tubing  20 . Construction of catheter  100  is otherwise the same as that of catheter  10 . 
     Referring to FIGS. 3A and 3B, a third catheter embodiment  200  of the present invention is depicted. Catheter  200  is similar in construction to both catheters  10  and  100 , but omits the fill tubing  14  and associated female connector  36  with plug element or cap  38 . Catheter  200  is configured for use as a reference, or abdominal, catheter in urodynamic procedures, placement thereof during such procedures having been previously noted above. 
     In the above-described embodiments, the outer tubing  12  is of 7 French (0.092 inch) diameter and formed of lubricious, soft, low durometer (˜60 Shore A) polyurethane or polyethylene with EVA (ethyl vinyl acetate), and is about 45 cm in length. Balloons  22  are of ˜0.3 inch in length, of ˜0.0002-0.0010 inch wall thickness, and formed of polyethylene with EVA. Outer tubing  12  is preferably marked in one centimeter increments for 30 centimeters and numerical five centimeter gradations to a twenty-five centimeter mark, beginning at the distal end of the most distal balloon  22 , which is ˜1 cm from distal end  16  of outer tubing  12 . If a second balloon is employed, as in catheter  10 , it is located ˜7 cm from distal end  16  of outer tubing  12 . Pressure lumen tubing  20  is preferably formed of polycarbonate or other substantially rigid thermoplastic and has an I.D. of between about 0.005-0.008 inch, as previously noted, and preferably ˜0.008 inch. Fill tubing is preferably formed of polyurethane or other semi-rigid thermoplastic having a durometer of Shore A and preferably has an I.D. of ˜0.035 inch. 
     In a manner exemplary of the fabrication of catheters  10 ,  100  and  200 , catheter  10  is formed by making a slit about 15 inches from the distal end  16  of outer tubing  12  and providing distal end  16  with a soft, rounded tip by techniques known to those of ordinary skill in the art. The exterior of outer tubing  12  is marked, as previously noted. A distal end of fill tubing  14  is notched at about a 45 degree angle (see FIGS. 1B and 2B) and inserted into outer tubing  12  from the proximal end thereof. Pressure lumen tubing  20   a  and  20   b  are inserted into outer tubing  12  through apertures  42   a  and  42   b  punched in side wall  34  at predetermined locations close to the distal end  16  of outer tubing  12  and threaded through outer tubing  12  proximally to the aforementioned slit in the side wall  34  thereof, where they exit. Then a mass of UV-curable adhesive  32  is injected into the bore  30  of outer tubing  12  through each of adhesive fill ports  44   a  and  44   b  extending through the side wall  34  of outer tubing  12  respectively adjacent apertures  42   a  and  42   b  so as to encompass the entry points of pressure lumen tubing  20   a  and  20   b  and isolate the bore  30  of outer tubing  12  therefrom (see FIGS.  4 A and  4 B). A suitable adhesive is UV 3321 offered by Loctite Corporation of Rocky Hill, Conn. Curing (cross-linking) of the UV-curable adhesive can be initiated in a very short time, as little as one to two seconds of exposure to UV-wavelength radiation. Curing of the adhesive also fixes the distal ends of pressure lumen tubing  20   a  and  20   b  in place, as well as fill tubing  14 . The excess distal length of pressure lumen tubing  20   a  and  20   b  is trimmed substantially flush with the exterior of the side wall  34  of outer tubing  12 . The proximal ends of fill tubing  14  and pressure lumen tubing  20   a  and  20   b  are sheathed with a protective sleeve or collar  35  of a heat shrink material (which is subsequently shrunken) over the area of the slit in outer tubing  12  where pressure lumen tubing  20   a  and  20   b  exits therefrom to prevent kinking, and then bonded to their respective connectors  36 ,  24   a  and  24   b , as known in the art. After the balloons  22   a  and  22   b  are formed and cut, they are placed and sealingly bonded at their longitudinal ends to extend over balloon fill ports  26   a  and  26   b , respectively, by heat-shrinking the longitudinal balloon ends, or cuffs, to the outer tubing  12  using a highly directional, hot-air stream. The balloons are baked at an elevated temperature, such as about 60° C. for about forty minutes to stabilize their respective volumes. Subsequently, a male plug element or cap  38  is placed on the fill tubing connector  36 , and the catheter is leak-tested, as known in the art. 
     Referring to FIGS. 5A through E and  6 A through E, the particulars of transducer assembly  300  according to the invention will be described. Transducer assembly  300  includes a two-piece, injection-molded plastic housing  302  which encompasses a transducer block  304  (FIGS. 7A,  7 B) having transducer recess  306  within which transducer  308  is received. A suitable transducer for use with the present invention is offered by Lucas Novasensor of Fremont, Calif. Transducer  308  is powered, and sends signals to a monitor, through conductors  310  of cable  312 , which extends to a monitor (not shown) as known in the art and is connected thereto with a compatible connector. Suitable monitors are offered by various companies, including without limitation Life Tech, Laborie, Dantec, MMS, Circon/Surgitek, and Brown Medical Monitors. There is preferably a Velcro® type hook patch (not shown) secured to the cable  312  or to transducer housing  302 , by which the cable  312  or housing  302  may be secured to the patient&#39;s leg using a disposable Velcro® type loop adhesive patch supplied with each catheter. 
     Transducer block  304  includes a manifold comprising a charging and vent passage  314  extending from a plunger bore  316  to a transducer port  318  opening into transducer recess  306 , transducer port  318  being faced by a sensor element, such as a diaphragm, of transducer  308 , the junction of port  318  and the transducer sensor element being sealed about the periphery thereof so as to be airtight, by techniques known in the art. Pressure lumen port  320  also communicates with passage  314  and extends to the bore of female luer connector  322 , which is configured to receive tapered male connector element  324  associated with a male luer lock connector  24 . Plunger  330  is received within plunger bore  316  and may comprise a plunger  330 a including a deformable cylindrical mass  332 , such as silicone, molded over a retention head  334  (see FIGS.  7 A and  7 B). In this embodiment, the diameter of mass  332  may be slightly less than that of plunger bore  316 , or vent grooves  335  may be formed in the plunger bore wall, the reason for which will be hereinafter explained. Further, if plunger  330 a is employed, the inner end  336  of plunger bore  316  may be formed as a cone or other suitable decreasing cross-sectional shape, mass  332  being deformable thereinto responsive to inward plunger movement to charge the air column between transducer  308  and a balloon  22  with a small volume of air. Alternatively, a plunger  330 b may be employed using an o-ring seal  340  about the inner end thereof (see FIGS.  8 A and  8 B). Again, the outer end of the bore may be enlarged to allow venting past o-ring seal  340 , or vent grooves  335  may be formed in the plunger bore wall. 
     Saddle-shaped plunger slide  350  is disposed on the upper portion of housing  302  and retained thereon by engagement of grooves  352  with tracks  354  of housing  302 . The outer end  356  of a plunger  330  extends through an aperture  358  in housing  302  between tracks  354  in a transverse orientation thereto. With plunger slide  350  in a left-most “zero” position (as depicted in FIGS.  5 A through  5 E), plunger  330  is in its outward-most position resting against leading inner flat  360   a  of plunger slide  350 , and the air column defined between transducer assembly  300  and a catheter  10 ,  100  or  200  is vented to the ambient environment through the enlarged plunger bore portion or vent grooves  335 . When plunger slide  350  is advanced to the right, as depicted in FIGS. 6A through 6E, inclined leading inner face  360 b of plunger slide  350  biases plunger  330  inwardly to close the air column and charge it with a very small volume, for example 15 μliters, of air, at which point plunger  330  resides under trailing inner flat  360   c  of plunger slide  350 . With plunger  330   a , mass  332  is deformed into inner end  336  of plunger bore  316  so as to reduce volume of the air column while effecting the charge by displacing air in inner end  336  of plunger bore  316  and closing off passage  314 . With plunger  330   b , o-ring seal  340  closes off the air column as it advances into the inner end of plunger bore  316  inwardly of vent grooves  335  (or a narrower bore portion, as the case may be) and charges the air column by displacing air trapped in inner end of plunger bore into passage  314 . FIGS. 7A and 7B are enlarged views of the plunger area of transducer block  304  with a plunger  330   a  respectively in zero and charged positions, while FIGS. 8A and 8B are enlarged views of the plunger area of transducer block  304  with a plunger  330   b  respectively in zero and charged positions. 
     When the air column is charged, the balloon  22  becomes at least partially filled with air, for example, 40% to 70% filled, but not completely filled, to prevent the balloon material from introducing artifact into a pressure reading. Thus, the flaccid, partially filled balloon  22  will prevent or at least significantly reduce the occurrence of aberrant effects in pressure detection due to temperature changes as dictated by Charles&#39; Law, or other aberrant effects attributable to the balloon wall, or inadvertent, external balloon compression. The volume of air which respectively fills a balloon  22  and its associated pressure lumen  20  and transducer assembly  300  will vary, depending on balloon and lumen length and internal diameter. However, it is preferred that the volume of air in the air column is such that at least fifty percent of the volume of air in the air column will remain in balloon  22 . The balloon will thus be sensitive to, and accurately transmit pressure from outside the balloon  22  to the balloon interior  28  and, through the coupling provided by the closed air column, to the transducer  308 , without the introduction of artifact from the balloon wall. In the disclosed embodiment wherein a 7 French diameter catheter outer tubing  12  is employed, charging the air column with the aforementioned ˜15 liters of air inflates a balloon  22  to about 0.105 inch diameter (8 French), which is believed to exhibit an accurate pressure response when employed in the urethral anatomy. 
     It is notable that plunger slide  350  may be manipulated by the clinician using a single hand by grasping housing  302  and moving plunger slide  350  using the thumb. It is also notable that the air column between each transducer assembly  300  and balloon or balloons  22  of a joined catheter  10 ,  100  or  200  may be vented, the monitor zeroed, and the air column accurately and repeatably re-charged as desired without removal of the catheter. 
     In use, a catheter such as  10  or  100  is inserted into a patient&#39;s bladder  400  (see FIG. 9) through the urethra  402  by techniques known in the art. Optionally, another, reference catheter  200  is inserted into the patient&#39;s rectum or vagina  404  (see FIG.  9 ), again as known in the art. After insertion, the pressure lumens of each catheter are respectively connected to a transducer assembly  300  in the zero, or venting mode or position, the monitor associated with each transducer assembly  300  zeroed, and then the balloons  22  charged by the aforementioned manipulation of plunger slides  350 . The transducers are automatically zeroed with the transducer assembly  300  in the zero, or venting mode, as ambient atmospheric pressure acts on both sides of sensor elements, such as diaphragms, of the transducers, before the air column is closed and charged. Thus, the air column charge is thus referenced against ambient pressure. Bladder filling may then be commenced through a fill tubing  14 , with attendant pressure data being accumulated by a monitor or monitors to which transducer assemblies are  300  connected by cables  312 , as known in the art. Other, conventional maneuvers may be performed, such as a VLPP study, again as known in the art. As bladder (or abdominal) pressure increases, deformation of a balloon  22  modifies pressure in its associated air column, which is transmitted to the transducer sensor element, such as a diaphragm, through the pressure lumen extending therebetween. Response of the sensor element to the pressure variation generates an electrical or other signal which is relayed to a monitor through the transducer cable  312 . 
     If a UPP procedure is to be initiated, a catheter  10  carrying two balloons  22  will be used. As known in the art, urethral pressure will be measured during withdrawal of catheter  10  from the bladder through the urethra using the most proximal balloon  22   b , while bladder pressure is monitored using balloon  22   a  at the distal end  16  of outer tubing  12 . As noted previously, the circumferential envelopment of outer tubing  12  of balloon  22   b  provides a pressure responsive element for effecting an accurate measurement of urethral pressure and urethral sphincter strength and integrity regardless of small anatomical anomalies of the urethra. Further, the presence of any such anomalies is more easily identified due to the circumferential contact of the balloon  22   b  with the urethral wall than by prior art, single reference, pin-point localized transducer elements such as micro-transducers and fiber optic transducers. 
     While the present invention has been described with reference to certain illustrated embodiments, those of ordinary skill in the art will recognize and appreciate that it is not so limited. Accordingly, additions, deletions and modifications to the embodiments of the invention as disclosed may be effectuated without exceeding the scope of the invention as encompassed by the claims following hereinafter.