Urodynamic testing in the diagnosis of small animal micturition disorders

Urodynamic Testing in the Diagnosis of Small Animal Micturition Disorders Richard E. Goldstein, DVM, DACVIM, DECVIM-CA* and Jodi L. Westropp, DVM, DACVIM†

Urodynamic testing provides a quantitative assessment of the function of the small animal lower urinary tract. Most commonly these techniques are utilized to assess urethral tone (urethral pressure profile or UPP) and bladder detrusor muscle function (cystometrogram or CMG). A UPP may be indicated in cases of canine and feline micturition disorders. Examples include suspected primary sphincter mechanism incontinence (PSMI), ureteral ectopia, other congenital abnormalities, suspected neurological disorders, and mechanical or functional urethral obstruction. A UPP can be performed effectively utilizing human dedicated equipment. A CMG may be indicated to assess detrusor function in all of the above cases as well as cases of suspected atonic or infiltrated urinary bladder. This procedure can also be performed using the same human equipment. These tests are useful not only in providing an accurate diagnosis, but also in providing a sensitive prognostic indicator for clinical outcome of micturition disorders with and without pharmacological or surgical therapy. A leak pressure point may also be established in dogs with urinary incontinence, and may be even more sensitive than a UPP to predict clinical incontinence in some cases. Clin Tech Small Anim Pract 20:65-72 © 2005 Elsevier Inc. All rights reserved. KEYWORDS urinary incontinence, primary sphincter mechanism incontinence, bladder atony, urethral profile pressure, cystometrogram

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rodynamic testing provides a quantitative assessment of the function of the small animal lower urinary tract. Most commonly these techniques are utilized to assess urethral tone (urethral pressure profile or UPP) and bladder detrusor muscle function (cystometrogram or CMG). Unfortunately, these tests are likely underutilized in veterinary medicine and are typically offered only in some universities or large referral centers. This is partly because of the expense of the dedicated equipment and the lack of experience of many of the veterinary practitioners and specialists, but also because of an existing misconception that these tests frequently provide inaccurate and unhelpful information in clinical practice. This review will assess the value and practicalities surrounding urodynamic testing in small animals, and will provide meaning-

*Department of Clinical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, New York. †Department of Medicine and Epidemiology, University of California, Davis, California. Address reprint requests to Richard E. Goldstein, DVM, DACVIM, DECVIMCA, Assistant Professor of Small Animal Medicine, Department of Clinical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY 14853. E-mail: [email protected]

1096-2867/05/$-see front matter © 2005 Elsevier Inc. All rights reserved. doi:10.1053/j.ctsap.2004.12.009

ful insight into when and how these tests can or should be performed.

The Urethral Pressure Profile A urethral pressure profile (UPP) is a valuable diagnostic tool for small animals with urinary incontinence (UI). Urinary incontinence can result from abnormalities in the micturition sequence originating from a variety of causes from spinal injuries to damage to the urethral sphincter, or from anatomic causes such as ectopic ureters. A combination of these problems has also been reported in some animals (eg, ectopic ureters and primary sphincter mechanism incontinence or PSMI).1 The diagnostic approach to urinary incontinence is complex and involves careful assessment of the signalment, history, physical examination, and pattern of urination as well as a minimal database (Table 1). Additional diagnostics are commonly performed before urodynamic studies in an attempt to exclude polyuria (eg, urine specific gravity, quantification of drinking, or urine output), and urinary tract infections (eg, urinalyses and urine cultures). Imaging such as ultrasound or radiographic con65

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Table 1 Common Examples of the Signalment and Clinical History Associated with Various Causes of UT in Dogs Disorder Ectopic ureters

Congenital urethral sphincter incompetence or urethral hypoplasia Acquired urethral sphincter incompetence

Signalment Young Females > males (causing incontinence) Northern breeds Young females Young to middle age Larger breeds

Urinary bladder dysfunction

Continuous leaking Affected since birth Continuous leaking Urge incontinence Resting incontinence Intermittent incontinence Pollakiuria Resting incontinence Post voiding incontinence Vaginitis Overflow incontinence Neurological deficits Easily expressible Overflow incontinence Neurological deficits Not easily expressible

Vaginal abnormalities

LS disease

History

Older dogs

T3-L3

trast studies are also commonly performed to rule out anatomic abnormalities in the urinary tract.

ies can be performed to more accurately evaluate the dog’s response to therapy.4

Indications for UPP

Suspected Increased Urethral Tone

Suspected Primary Sphincter Mechanism Incontinence Primary sphincter mechanism incontinence (PSMI) appears to be the most common and frequently most frustrating disorder that causes incontinence in dogs. Most often, middle aged, female spayed dogs are affected, but younger and intact females as well as male dogs can also be affected.2 When urodynamic testing is not performed, PSMI is usually diagnosed by exclusion, once spinal problems and other forms of urinary incontinence have been deemed unlikely, as well as by response to therapy. A UPP can be helpful in documenting the abnormality, and potentially will allow the clinician to predict response to therapy.3 Often dogs suffer from multiple abnormalities of the lower urinary tract, making an accurate diagnosis even more important. For instance dogs with ectopic ureters have been found to frequently also suffer from concurrent PSMI.1 Therefore, performing a UPP before surgical correction of the anatomic abnormality can be beneficial, the results useful for prognostic purposes and for guiding therapy postsurgery. When sphincter abnormalities are suspected the veterinary practitioner has 2 options; (1) To attempt trial therapy or (2) to perform a UPP. In the authors’ opinion trial therapy with an alpha adrenergic agonists like phenylpropanolamine (PPA) when PSMI is suspected in a dog with an appropriate signalment, history, and normal minimal database (including a urine culture) is an acceptable diagnostic and therapeutic pathway. However, full urodynamic testing (including a UPP and CMG) can be helpful at that time to achieve a definitive diagnosis, as well as to rule out concurrent disorders and provide to baseline data in case the dog does not respond to alpha adrenergic agonist. If not performed sooner the UPP should be utilized in those cases that fail trial alpha adrenergic agonist therapy. In these cases the UPP will help to document an abnormally low urethral tone and subsequent stud-

Occasionally, dogs present for UI when the urethral tone is so high, that urination occurs only when high pressures are achieved in the bladder at which time urine passively leaks out. This is frequently referred to as overflow incontinence. Before performing a UPP additional causes of overflow incontinence should be considered (see section on CMG). A mechanical obstruction should be ruled out using appropriate imaging techniques. Causes of mechanical obstruction include urethroliths, urethral plugs, urethral neoplasia, proliferative urethritis, and foreign bodies. Functional obstructions and urethral spasms can occur secondary to a mechanical obstruction, but can also be idiopathic. In cases where a mechanical obstruction cannot be documented a UPP may be the most appropriate diagnostic test.5 It is also possible that owners perceive the dog to be incontinent, but on further questioning the dog is truly pollakiuric and stranguric because of increased urethral tone. A thorough neurological examination should be performed to exclude intervertebral disk disease resulting in an “upper motor neuron bladder” when the internal and or external sphincters do not have the necessary inhibition to allow the passage of urine.

Reflex Dyssynergia Idiopathic autonomic un-coordination between the sympathetic and parasympathetic nervous system can result in UI and is called reflex dyssynergia. This disorder is more commonly seen in middle aged, large breed male dogs.6 A UPP can help document the elevated urethral tone, and can localize the problem to the part of the urethra most affected. It can also be used to more objectively monitor and guide the response to pharmacologic therapy.

Suspected Ureteral Ectopia A UPP can also be of benefit for prognostic purposes in dogs with ectopic ureters and the author’s routinely perform uro-

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dynamic studies on young dogs with suspected ectopias. This is because of the suspected high incidence1 of concurrent congenital disorders of ectopic ureters and PMI. Owners should be warned of this before surgical correction of ectopic ureters if a UPP is not performed at that time.

Performing the Procedure Many large centers including the University of California at Davis (author JW) use the Urovision Janus V system by Life Tech (Urolab® System V. Life Tech, Inc., Stafford, TX, Website: http://www.life-tech.com) (Fig. 1). This uniformity in equipment perhaps will allow more reliable data comparisons to be made among various studies in different institutions in the future (assuming similar anesthetic regimens are employed; see below). This system is easy to use, stores data, and allows importation of data to other computer programs such as Microsoft® Word and Power Point. The machine is easily calibrated for any urodynamic procedure with the three transducers placed at the level of the patient’s bladder (Fig. 2). Normal values for each machine should be established under the same anesthetic protocol. After an anesthetic choice is made (see below), a triple lumen catheter (Life Tech, Inc.; and Cook Urological Inc., Spencer IN, Website: http://www.cookurological.com) (Fig. 3) is aseptically placed into the bladder. The catheter is then connected to pressure transducers that

Figure 2 Urethral profile set up using the Life Tech Urovision Janus V®. Note the 3 transducers utilized for this procedure.

Figure 1 Urovision Janus V system by Life Tech, Inc.

measure intravesical and urethral pressures. The last port is connected to the fluid line for administration of sterile water at a constant rate, usually 2 mL/min via an infusion pump. The urethral catheter is mechanically withdrawn from the urethra at a constant standard rate (usually 0.5-1 mm/s). Most urodynamic machines can now provide or calculate the relevant data needed to interpret a UPP. The maximal urethral pressure (MUP) is recorded during the withdrawal phase of the UPP. The computer’s software will provide a tracing of this pressure as the catheter is slowly withdrawn. The intravesical pressure is also recorded throughout the study. The software is capable of calculating the maximal urethral closure pressure (MUCP) as the difference between the MUP and the perfused intravesical pressure. Lastly, the functional profile length (FPL) is calculated as the portion of the UPP tracing during which the urethral pressure exceeds intravesical pressure. This value, combined with the MUCP, is thought to be the most clinically useful in predicting sphincter competence. Some clinicians also like to evaluate the functional area (FA), which is calculated as the area under the FPL curve. Again, most modern urodynamic machines will provide this data for easy interpretation. A schematic of the pertinent information is provided in Fig. 4 and an actual tracing using the Urovision Janus V system in Fig. 5.

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Figure 3 Life Tech triple lumen catheter used for urethral pressure profilometry.

Anesthetic Considerations All anesthetics studied have the potential to decrease urethral tone to some extent.7 Therefore, it is ideal to perform a UPP without any chemical restraint. In many animals, especially male dogs, this can accomplished, however, in many females, some puppies, and fractious or painful animals, the catheterization can be difficult without tranquilization or anesthesia. Some clinicians have advocated the use of placing a small amount of sterile lidocaine jelly in the vestibule 10 to 15 minutes before attempting catheterization. Although this should not affect a UPP, no studies are available to document what, if any, affect this treatment has on the urethral tone. Studies have evaluated the effects of some drugs on the UPP in dogs.8-10 Xylazine, an alpha 2 agonist, significantly lowers urethral closure pressure (MUCP) and alters urethral sphincter electromyographic activity as well.8 The more specific alpha 2 agonist, medetomidine, is not recommended either because of its effects on the urethral closure pressure and inconsistent results obtained after intramuscular injection of the drug.9 To the authors’ knowledge, no intravenous studies have been performed to evaluate medetomidine given in this manner. Propofol appears to be the injectable anesthetic that causes the least interference with UPP measurement at this time.10 Inhaled anesthetics such as, halothane has also been reported to decrease urethral tone by as much as 45 to 90% compared with dogs without anesthesia. To the authors’ knowledge, no studies evaluating isoflurane are reported in the literature, but sevoflurane has been tested recently and shown to be a good anesthetic option if needed to maintain anesthesia after propofol induction.11 Because the CNS effects of propofol are short, though, the clinician can sedate the animal with propofol (4-6 mg/kg slow bolus), place the urinary catheter and allow the dog to recover to where they could maintain sternal recumbency without assis-

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MUCP

cmH2O MUP

tance. Then, ideally, the dog can be restrained in right lateral recumbency for the UPP procedure. For more fractious patients, studies have evaluated performing a UPP under varying doses of proprofol as well as the inhalant, sevoflurane. No significant differences in the MUP, MUCP, or FPL were noted as doses of propofol less than 0.8 mg/kg/min of a constant rate infusion of propofol in healthy beagle dogs.11 The authors did comment that plasma concentrations of propofol can be variable in different dogs. Muscle hypertonicity and tremors were noted that can cause artifact on the UPP recordings. Propofol can also be costly, especially in large breed dogs. When sevoflurane was evaluated, the authors found that if the inhalant is used at ⬍2.0%, reliable UPP parameters could be obtained.11 A capnograph system that measured the endotracheal tube inhalant and carbon dioxide concentrations were monitored closely during the study, which would appear to be essential for obtaining reliable readings.

The Cystometrogram Cystometry is a useful diagnostic test for evaluating urinary incontinence and is unfortunately even more underutilized by many clinicians than the UPP. A cystometrogram (CMG) can provide information about detrusor elasticity and capacity as well as information about bladder volumes and threshold pressures. With the advent of newer, more effective anticholinergics (tolterodine or the investigational drug, duloxetine), this diagnostic procedure is being recommended more often for patients with micturition abnormalities.

Indications for This Test Detrusor instability can occur from a variety of causes including bacterial cystitis, urolithiasis, neoplasia, polypoid cystitis, or can even be idiopathic. Before performing a CMG, the animal should first be evaluated for the causes mentioned above, including imaging, urine cultures and possibly cystoscopy. If such a cause for the clinical signs is discovered and clinical signs improve with appropriate therapy then no further testing is likely warranted. However, if no underlying cause is found or if clinical signs persist despite therapy, a CMG may be indicated. Possible indications: 1. Urinary incontinence: Suspected PMSI or ureteral ectopia.

FPL

Time (sec) or Distance (mm)

Figure 4 Schematic drawing of a urethral pressure profile in a normal female dog. MUP, Maximal urethral pressure; MUCP, Maximal urethral closure pressure; FPL, Functional profile length.

Cystometrograms are helpful to determine if concurrent detrusor abnormalities are present in dogs with suspected PSMI, ectopic ureters or in cases where an animal is refractory to conventional treatment for their suspected cause of urinary incontinence. Evaluating bladder storage function is recom-

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Figure 5 Actual tracing of a UPP in a female dog. Note a low MUP of 65 cm H2O.

mended for all animals with urinary incontinence, especially those refractory to standard treatment with the alpha agonists or hormones. Dogs with ectopic ureters should also have their bladder function evaluated because detrusor instability may contribute to the urinary incontinence and possible poor surgical outcome. 2. Overflow incontinence: Suspected atonic bladder Atonic bladders can be diagnosed by using CMG in dogs with apparent overflow incontinence and large expressible urinary bladders. This test may also be helpful to record an animal’s response to drug therapy. Bladder atony is typically causes by primary nerve damage or muscle damage caused by stretching of the detrusor muscle and detachment of the muscle fiber tight junctions. Detrusor stretching is typically secondary to neurological disorders, infrequent urination, urethroliths, urethral plugs, strictures, or urethral neoplasia. By evaluating the threshold volumes and pressures, a CMG is a useful diagnostic tool for the clinician. The disadvantage of a CMG is the need for sedation for most patients and the limited choices of appropriate anesthetic drugs for this procedure (see below).

Performing the Procedure Once the animal is sedated, a double lumen urinary catheter (Life Tech, Inc. and Cook Urological Inc.) (Fig. 6) is aseptically placed into the urinary bladder of the dog. One of the ports is connected to the pressure transducer on the machine and the other port is utilized for fluid administration. For more precise intravesicle pressure measurements, it is ideal to measure abdominal pressure as well. This can be accomplished by manually removing any feces from the distal colon

and inserting a rectal catheter to provide an estimate of abdominal pressure (Life Tech, Inc.). The catheter is inserted to approximately the seventh lumbar vertebrae and then it is connected to the appropriate pressure transducer. Once all of the ports are correctly connected to their respective transducer or fluid line, sterile water is infused at a constant rate. Pressures are measured as the bladder is being filled with water thus indicating the degree of compliance of the bladder. Eventually in a normal bladder, being infused with water, a urination reflex (detrusor reflex) is triggered. The pressure generated at this time is also characterized and analyzed. A schematic of a CMG is shown in Fig. 7 and one obtained on a cat using the Urovision Janus V system is shown in Fig. 8. The various components are referred to as tonus limbs. Tonus limb I reflects the resting bladder pressure. The second tonus limb represents compliance and is reported as the change in pressure per 100 mL of infusate. Tonus limb III is rarely seen in humans and dogs. It is reported to reflect the collagen component of the bladder wall stretch. The rate at which the bladder is filled is controversial. Each facility must establish normal values for their equipment and flow rates and it would be ideal for institutions to establish standardized flow rates to be able to compare various studies among institutions. One must realize that slow and fast infusion rates evaluate different responses from the bladder. Infusion rates for animals have been reported between 5 to 50 mL/min.12-15 Klevmark has evaluated various fill rates in humans and cats.13-15 Conventional cystometry using high nonphysiological filling rates creates an artificial condition with continuous pressure rise, and impairs the clinician’s ability to truly understand compliance of the bladder. The pressure rise in the bladder is actually rate-dependent and

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Figure 6 Life Tech double lumen catheter used for cystometrograms.

not volume-dependent. Thus, the threshold pressure when the detrusor responds reflects only the reaction of the bladder’s response to excrete urine at a high rate and is not coordinated with bladder filling. When evaluating humans during a CMG, Klevmark and co-workers found that when using high fluid rates, the CMG reported increased volume threshold for micturition, impaired detrusor contractility and lower sensitivity for detecting spontaneous phasic detrusor activity. They speculated that high fluid rates could cause mechanical trauma to receptors, nerve endings, cells, and cell junctions, which are temporarily functionally disturbed. According to Klevmark, the “collecting phase of the bladder was identical to the process of rapid retrograde filling through a catheter.” Filling rates that are higher than physiologic rates do not illustrate the bladder behavior in the true collecting phase.15 Therefore, through several cystometric studies in cats and humans, he defined the hour diuresis (HD) unit to be 1.1 mL/kg/h for cats and 1 mL/kg/h for humans. If a large amount of fluid is consumed, the maximum excretion rate is 15 HD. Therefore, a 5 kg cat excreting 15 HD would correspond to 82.5 mL/h, however, this corresponds to only 1.3 mL/min. Most pumps on the Janus V Urodynamic equipment cannot be calibrated to infuse this slow. Moreover, it would take at least 30 to 40 minutes for a small cat to have a detrusor reflex at this rate. In the clinical setting, it would be nearly impossible to perform a CMG on a medium size dog at these rates. When we perform CMGs on cats, we generally infuse fluid at a rate of 40 to 45 HD (approximately 4 mL/min in most cats), which is considered to be a medium-high fill rate according to Klevmark’s studies.13-15 In a recent study Hamaide and co-workers evaluated retrograde filling cystometry at 5, 10, and 20 mL/min in clinically healthy intact female beagle dogs weighing between 12.5 to 20 kg.12 For a 20 kg dog this would correspond to approximately 50 to 62 HD if filling rates are similar between species. They compared the threshold volumes, pressures, and compliance to a procedure called, diuresis cystometry. The latter method was performed by placing a urinary catheter, giving a standard dose of IV furosemide and then infus-

ing 20 mL/min of IV fluids to simulate more physiologic bladder filling. Threshold volumes were not different among the three retrograde infusion rates, but were significantly lower than diuresis cystometry. Threshold pressures were significantly higher at the 20 mL/min retrograde infusion rate. The authors recommended retrograde infusion rates no higher than 20 mL/min for medium size dogs. As a practical approach to the CMG, the clinician must also calculate approximately how long the procedure will take, which will vary depending on which fluid rate is used. Some researchers have reported stopping the CMG once the intravesical pressure is ⬎40 cm H2O, regardless if a detrusor reflex is noted. Hematuria has been noted frequently as pressures exceeded this value. However, fill rates in these reports were always higher than 20 mL/min and it is possible that hematuria is because of the rapid fluid insuflation and not the pressure achieved. At lower fill rates, higher pressures are probably safe for the animals. In one author’s experience performing CMGs in cats without anesthesia, we routinely noted threshold pressures of ⬎70 cm H2O with no adverse affects.

Anesthesia Just like the UPP, all drugs affect the detrusor reflex to some extent. Many drugs can abolish the reflex (eg, gas inhalants)

Vesicular Pressure cmH2O

Detrusor Reflex

Fill Volume (ml)

Figure 7 Schematic drawing of a CMG in a dog.

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Figure 8 Actual tracing of a CMG performed in an awake cat.

and ideally a CMG should be done awake. Often, this is not practical for animals though because they will not cooperate and excess artifact will prevent reliable readings. However, experimentally, we have performed CMGs on awake cats. The cats were first anesthetized with isoflurane and a double lumen catheter was aseptically placed. Each cat was allowed to recover completely and then gently restrained in right lateral recumbency or allowed sit quietly on the technicians lap during the procedure. We were able to obtain interpretable readings in these cats, although studies were only performed on a small number of cats. Various sedatives have been evaluated in dogs for a CMG and the one that appears to inhibit the detrusor reflex the least and provide reproducible tracings is the alpha 2 agonist, xylazine.16 In 1 report, premedication with atropine did not appear to affect the detrusor.17 The more selective alpha 2 agonist, medetomidine had similar threshold volumes and pressures as xylazine.9

The Leak Point Pressure Although not routinely performed, a leak point pressure (LPP) has been reported in studies in healthy dogs and in models of urinary incontinence.18,19 LPPs were originally used to evaluate women with various forms of suspected “stress incontinence.” LPPs may be the first indication of abnormal urethral tone, even when the UPP is considered normal. The LPP is thought to be the most accurate method of predicting clinical response to colposuspension for the treatment of urinary incontinence in female dogs.19 The LPP has been modified from humans and can be performed in dogs. Anesthesia needs to be implemented for this procedure and propofol appears to be the drug choice in preliminary studies. Similar anesthetic regimens documented in the UPP can be followed. Once the animal is anesthetized, a sterile urinary catheter is placed aseptically into the urethra, the bladder evacuated, and the dog placed in dorsal recumbency. The catheter is then connected to the pressure transducer and

72 baseline intravesical pressures recorded. Next, a large indirect blood pressure cuff is placed around the animal’s abdomen, just cranial to the bladder. It is important not to inflate the band until baseline bladder pressure measurements are obtained. Next, the bladder is infused with 50 to 75 mL of sterile water (most report fast infusion rates), and then the abdominal cuff is inflated to at least 80 cm H2O. If no “leak” is noted, additional pressure can be placed on the animal’s abdomen between the 2 most caudal pairs of teats, while an assistant carefully observes the animal for fluid leaking from the urethra. The minimum intravesical pressure necessary to cause external leakage is recorded as the LPP. Additional amounts of sterile water (or saline) can be infused and the procedure repeated until the LPP is obtained. The volume of infusate and LPP are then recorded.

References 1. Lane IF, Lappin MR, Seim HB 3rd: Evaluation of results of preoperative urodynamic measurements in nine dogs with ectopic ureters. J Am Vet Med Assoc 206:1348-1357, 1995 2. Ling GV: Disorders of urination, in Ling GV (ed): Lower Urinary Tract Diseases of Dogs and Cats. St. Louis MO, Mosby-Year Book, Inc., 1995, pp 191-206 3. Richter KP, Ling GV: Clinical response and urethral pressure profile changes after phenylpropanolamine in dogs with primary sphincter incompetence. J Am Vet Med Assoc 187:605-611, 1985 4. Ling GV: Urodynamic testing techniques for disorders of urination, in Ling GV (ed): Lower Urinary Tract Diseases of Dogs and Cats. St. Louis MO, Mosby-Year Book, Inc., 1995, pp 93-98 5. Lane IF, Fischer JR, Miller E, et al: Functional urethral obstruction in 3 dogs: Clinical and urethral pressure profile findings. J Vet Intern Med 14:43-49, 2000 6. Diaz Espineira MM, Viehoff FW, Nickel RF: Idiopathic detrusor-urethral dyssynergia in dogs: A retrospective analysis of 22 cases. J Small Anim Pract 39:264-270, 1998

R.E. Goldstein and J.L. Westropp 7. Richter KP: Use of urodynamics in micturition disorders in dogs and cats, in Kirk RW (ed): Current Veterinary Therapy X. Philadelphia, W.B. Saunders, 1989, pp 1145-1150 8. Richter KP, Ling GV: Effects of xylazine on the urethral pressure profile of healthy dogs. Am J Vet Res 46:1881-1886, 1985 9. Rawlings CA, Barsanti JA, Chernosky AM, et al: Results of cystometry and urethral pressure profilometry in dogs sedated with medetomidine or xylazine. Am J Vet Res 62:167-170, 2001 10. Combrisson H, Robain G, Cotard JP: Comparative effects of xylazine and propofol on the urethral pressure profile of healthy dogs. Am J Vet Res 54:1986-1989, 1993 11. Byron JK, March PA, DiBartola SP, et al: Comparison of the effect of propofol and sevoflurane on the urethral pressure profile in healthy female dogs. Am J Vet Res 64:1288-1292, 2003 12. Hamaide AJ, Verstegen JP, Snaps FR, et al: Validation and comparison of the use of diuresis cystometry and retrograde filling cystometry at various infusion rates in female Beagle dogs. Am J Vet Res 64:574-579, 2003 13. Klevmark B: Motility of the urinary bladder in cats during filling at physiological rates. I. Intravesical pressure patterns studied by a new method of cystometry. Acta Physiol Scand 90:565-577, 1974 14. Klevmark B: Motility of the urinary bladder in cats during filling at physiological rates. II. Effects of extrinsic bladder denervation on intramural tension and on intravesical pressure patterns. Acta Physiol Scand 101:176-184, 1977 15. Klevmark B: Natural pressure-volume curves and conventional cystometry. Scand J Urol Nephrol Suppl 201:1-4, 1999 16. Johnson CA, Beemsterboer JM, Gray PR, et al: Effects of various sedatives on air cystometry in dogs. Am J Vet Res 49:1525-1528, 1988 17. Barsanti JA, Finco DR, Brown J: Effect of atropine on cystometry and urethral pressure profilometry in the dog. Am J Vet Res 49:112-114, 1988 18. Rawlings CA, Coates JR, Chernosky A, et al: Stress leak point pressures and urethral pressure profile tests in clinically normal female dogs. Am J Vet Res 60:676-678, 1999 19. Rawlings C, Barsanti JA, Mahaffey MB, et al: Evaluation of colposuspension for treatment of incontinence in spayed female dogs. J Am Vet Med Assoc 219:770-775, 2001