Surgery – Diagnostic testing – Measuring fluid pressure in body
Reexamination Certificate
2000-02-15
2002-09-10
Shaver, Kevin (Department: 3736)
Surgery
Diagnostic testing
Measuring fluid pressure in body
C600S435000, C604S915000
Reexamination Certificate
active
06447462
ABSTRACT:
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'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 h
Cutler Christopher A.
Dixon Richard A.
Smith Steven R.
Wallace Wm. Dean
Clinical Innovation Associates, Inc.
Marmor II Charles
Shaver Kevin
TraskBritt
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