Urodynamics is the study of the bladder and urethra, and is generally used as a means for diagnosing disorders such as urinary incontinence, benign prostate hyperplasia, pelvic organ prolapse, and other medical conditions that affect the functioning of the lower urinary tract. This article will go through the main types of commonly performed urodynamic tests, current problems in urodynamics and a theoretical approach on how to overcome them.
Uroflowmetry is test which measures natural urine flow rate, as well as urine volume. Patients are asked to empty their bladders into a specially equipped toilet that records data such as urine flow rate. This test is routinely performed for standard urodynamic assessments, and is useful when diagnosing weak urine stream or difficulty urinating. Uroflowmetry can also provide data about a patient’s bladder or sphincter function, and can be used to determine if obstructions are blocking the normal flow of urine.
Pressure uroflowmetry is similar to uroflowmetry in that this test also measures the rate of urination. However, bladder and rectal pressures are simultaneously recorded during this assessment. Pressure uroflowmetry requires invasive catheterization and is used for diagnosing disorders that result in difficulty urinating. Common problems that are diagnosed with this test are bladder muscle weakness and bladder outlet obstruction.
Post-void residual volume tests are used to measure the urine volume that remains after voiding. This urodynamic test is used for many urinary tract disorders. Patients are asked to void their bladders naturally, and then a bladder scanner is used to noninvasively measure the volume of urine remaining in the bladder, or the patient is catheterized.
Post-void residual volume assessments are used to determine neurogenic bladder disorders as well as the cause of frequent urinary tract infections, renal insufficiency, bladder outlet obstruction, and detrusor underactivity.
Multichannel cystometry is an invasive form of pressure uroflowmetry. Two pressure catheters are inserted into the patient, one in the bladder and one in the rectum, to measure associated pressures during the filling and the emptying of the bladder. Measurements include the presence of contractions in the bladder wall during filling or stress (i.e. coughing), urethra strength, detrusor under- or overactivity, and bladder outlet obstruction. This test is the gold standard for diagnosing stress urinary incontinence.
Electromyography measures the electrical activity in the bladder neck. This test can be performed during urination to determine coordinated or uncoordinated voiding and the functioning of the detrusor muscle. For this measurement, electrodes are placed in the pubic area of the patient to test for electrical impulses from the muscles. Most commonly, electromyography is beneficial when testing for neurologic disorders that affect the communication between the brain and body.
Urethral pressure profilometry measures strength of sphincter contractions and is commonly used to study urinary incontinence in women.
Fluoroscopy (also known as videourodynamics) is a moving video x-ray of the bladder and bladder neck that is procured while the patient voids his or her bladder. This test provides pictures of the lower urinary tract and can be used to make diagnoses, such as bladder outlet obstruction or pelvic organ prolapse.
Ultimately, each of the tests described above is common during a routine urodynamics assessment. These tests range from non- to minimally invasive and are performed as outpatient procedures.
Current Problems in Urodynamics
Although the tests described above provide a lot of data for physicians and urologists, few technological advancements have been made recently in the urodynamics field. Indeed, urodynamic testing has been the gold standard for assessing the lower urinary tract for more than 30 years.
While there have been important innovations to the instruments that are used during these assessments, and clinical knowledge of conditions that affect the lower urinary tract has improved, there are still issues surrounding this practice that should be resolved if urodynamics is going to remain relevant.
The history of urodynamic testing begins with noninvasive uroflowmetry, where the characteristics of a patient’s urine stream are studied. Next, pressure flow studies were introduced which involved invasive catheterization. Since that time, few changes have been made. The most recent technological advancement has been the use of fluoroscopy for noninvasive videourodynamics.
Over the past 30 years, innovations such as air charged bladder and rectal catheters (which overcome the limitations of water charged catheters), electromyography electrodes, and automated puller systems have improved data acquisition during urodynamic tests. However, the ability to gain more knowledge in a technologically advanced manner has come at a huge cost.
In addition to the start up and maintenance fees for the urodynamic testing equipment, each test costs a minimum of $5001. If videourodynamics are utilized, there is a significantly higher associated cost. With the unknown future of health insurance and Medicare in the United States, the high cost of these procedures is a current drawback, particularly when many diseases of the lower urinary tract are not life-threatening.
Another problem that surrounds the current state of urodynamic testing is variability clinical outcomes, despite the fact that this type of testing provides an impressive amount of data for urologists. For instance, recent studies have suggested that urodynamic testing does not always result in superior outcomes for patients with uncomplicated and demonstrable stress urinary incontinence. It should be noted that the preceeding statement is not true for most other urinary complications.
A third, present limitation of urodynamic testing is patient comfort and dignity. Urodynamics requires for a patient’s genitals to be handled and for activities that are generally very private (i.e. urination) to occur in front of one or more observers. When catheterization is necessary, the test is invasive and can be uncomfortable. Following the test, patients occasionaally report sustained discomfort and urinary tract infections2. Non-invasive procedures that reduce the risk of pain and infection will be necessary in the future in order for urodynamic testing to remain relevant.
Overcoming Existing Problems: The Future of Urodynamics
Although urodynamics is a powerful tool in the study of lower urinary tract complaints, the system is not perfect, as outlined above. Discussed here are methods and techniques that are expected to overcome these issues and indeed, are the future of urodynamics.
Perhaps one of the largest innovations that will occur over the next 10 years is the development of non-invasive methods that will eliminate the need for painful and embarrassing catheterization. Many such methods are currently being tested.
Non-Invasive Doppler Ultrasound Videourodynamics
At present, detrusor pressure measurements require the use of 2 catheters – one in the urethra and one in the anus – in order to obtain the necessary data. For many years, urologists have dreamed of a non-invasive manner in which to acquire this data. Not only are current tests painful and emotionally uncomfortable for patients, but their use can obscure data due to the patient’s discomfort.
A completely non-invasive transperineal urodynamic method that uses Doppler ultrasonography3 for acquiring measurements such as detrusor pressure as well as urine flow has been developed. Initially, urine flow was assumed not to produce Doppler effects due to lack of blood cells. However, it is now understood that microbubbles are formed in the urine stream which can be detected by Doppler ultrasonography.
In this initial study, patients sat on a commode and had a probe advanced (via remote control) towards them until gentle contact was achieved between a sensor and the perineal skin. After urination, uroflow data and Doppler ultrasound video data were collected.
This method showed utility in diagnosing the degree of bladder outlet obstruction in patients, and had important advantages such as speed, effectiveness, and simplicity. When utilizing this method the patient is allowed to void freely, better simulating at-home conditions, and there is no uncomfortable contact between penis and equipment. Indeed, for urodynamic measurement to remain relevant, non-invasive techniques will be required for the measurement of voiding function in the future.
Non-invasive Penile Cuff for Improved Clinical Outcome
An exciting innovation that addresses two current problems with urodynamics – invasiveness and poor clinical outcomes – is the penile cuff.
The penile cuff is a non-invasive urodynamic test that has shown utility as an alternative to pressure-flow studies. The penile cuff is a small, inflatable cuff that is similar to a blood pressure cuff. This cuff is placed on a patient’s penis and is gradually inflated and deflated in order to obstruct urine flow several times during urination. The pressure that is applied to the penis which ceases urine stream is equivalent to the urethral closing pressure. In one study4, the penile cuff was shown to correctly predict prostatic obstruction 79% of the time, with 100% sensitivity and a specificity of 63%. Positive predictive value was 68%, while negative predictive value was 100%.
In addition to having diagnostic utility, the penile cuff can be used for predicting clinical outcomes5 prior to diobstructive surgery when prostatic obstruction is suspected. At present, pressure-flow studies are used for diagnosis; however, they are costly, uncomfortable, and inconvenient for the patient.
In this study, patients that were undergoing surgery for prostatic obstruction who had been diagnosed without catheterization received the penile cuff test and completed an International Prostate Symptom Score survey. A total of 62 patients, who ranged 49 – 86 years old with a mean age of 70 participated in the study. Of the 62 patients, 38 underwent transurethral resection while 24 received holmium laser enucleation of the prostate. The mean International Prostate Symptom Score for patients prior to surgery was 21, with a range of 5 – 35.
Two months following diobstructive surgery, patients completed a second International Prostate Symptom Score survey. After surgery, the mean symptom score dropped to 11, with a range of 1 – 31. Of the 62 patients that underwent treatment, 35 were predicted to be obstructed, while 27 were not. Of the 35 obstructed patients 94% had a successful clinical outcome, while 70% of those not predicted to be obstructed also had a successful clinical outcome following surgery. A clinically successful outcome was defined as an improvement of 7 or greater on the survey.
The penile cuff test was therefore shown to be an exciting new way to perform traditional urodynamic tests, particularly when prostatic obstruction is assumed. This technology is at the forefront of the future of urodynamics.
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Catheterless Long-Term Ambulatory Urodynamic Measurement
As previously mentioned, significant impediments to urodynamics testing are invasiveness, as well as the inability to accurately recreate physiologic symptoms. A long term solution – and indeed the future of urodynamics – is to create an ambulatory, catheterless system6 for long term measurement that will help physicians better understand voiding disorders. This solution is particularly attractive for patients with overactive bladder, who often show normal results during clinical exams. Here, a three part urodynamic measurement system that has shown promise in preliminary testing will be discussed.
The system that was developed consists of an intravesical capsule that is combined with a hand-held device used to register the patient’s desire to void and micturition, as well as an alarm pad that detects urine loss.
The intravesical capsule, called the Willes Capsule, is a flexible, C-shaped capsule that is inserted via cytoscope directly into the bladder. This pressure measurement capsule has a microelecrodemechanical pressure sensor, a microcontroller, and EEPROM which stores pressure data. Communication between components occurs through an IC bus. The entire system operates on 2.5 V, provided by two batteries.
Measurement frequency of 4 Hz enables measurement of fast pressure changes due to contractions, such as those that occur as a result of coughing. The C-shape of the capsule minimizes the risk of it being expelled from the bladder during micturition. Removal of the capsule, however, is easily performed by a physician. In vitro cytotoxicity studies thus far have been promising.
The handheld device is designed in order to create a digital voiding diary that is synchronized with changes in the pressure measurement and alarm pad. This device also consists of a 2.5 V power supply, a microcontroller, and EEPROM for storage of diary data.
An alarm pad is used to detect urine loss. This pad contains similar electronics as the other components described above, and is similar to what is used when treating enuresis patients.
Thus far, the Willes capsule and the three-component ambulatory system have only been used on models of the female bladder, and not yet in a clinical trial setting. However, this innovation is an important representation of the future of urodynamics, which will require tools that allow for long term measurement in order to overcome the present difficulties with traditional testing.
Cystometry with Gas Perfused Catheters with Helium
Another innovation in urodynamics which may represent the future of the field in the immediate future is cystometry with gas perfused catheters with helium. This gas perfusion method has been compared to water perfusion, especially in use for cystometry in children as a way to overcome patient discomfort as well as inaccuracies when water charged catheters are used.
In this study, pressure changes were first measured using the gas perfusion system in an artificial bladder under different conditions in order to determine this method’s utility. No significant pressure changes were recorded when the artificial bladder was moved into varying positions.
Next, 62 urodynamic measurements were recorded from 33 patients that ranged in age from 5 months to 25 years. Throughout the recordings, 562 active or passive provocation tests were performed. Simultaneous measurement of pressure change amplitudes in real time with the bladder and two double channel catheters placed in the urethra were recorded. Velocity of pressure increase could be compared with the traditional water perfusion catheter.
Ultimately, the gas perfusion system had many advantages versus the water perfusion system, especially for use in small children. With the gas perfusion system, reliable measurements could be made regardless of the child’s body position or movements. Additionally, the gas perfusion catheter responded to pressure changes more quickly during provocation and stress tests. Overall, urodynamics with gas perfusion of helium was shown to be a worthwhile alternative to water perfusion.
While this study does not achieve the goal of reduced invasiveness, it does fill a gap in the urodynamics field that needs to be addressed. Children commonly undergo urodynamics testing for a variety of reasons, and it is important to make these sessions as reliable, quick, and accurate as possible.
With present methods, artifacts in the measurements are common, particularly when the patient moves. Since children are unpredictable in their movements, this disadvantage can lead to a series of expensive, painful, and embarrassing tests needing to be repeated. Part of the future of urodynamics is improving the current technology in order to improve present functionality.
Conclusion
Ultimately, the future of urodynamics lies in the creation of cost-effective methods for reliable diagnosis of urinary complaints. While the dream of non-invasive, ambulatory methods for assessing bladder function is likely still a decade away, there have been a number of innovations that are bringing this goal closer to reality. The reduction of artifacts, as well improvement to patient comfort and the removal of observers will be necessary for urodynamics to remain relevant as a clinical practice.
More clinical research must also be performed in order to prove the utility of urodynamics for diagnostic use, particularly relative to surgical outcomes. Without more research, the future of urodynamics is dim due to the high cost of testing and difficulty for reimbursement from Medicare or health insurance companies. Overall, the future of urodynamics will rely upon innovation, research, and the development of noninvasive techniques.
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References
- Smith AL, Wein AJ. Predicting the future of urodynamics. Translational Andrology and Urology. 2012;1(2):76-77. doi:10.3978/j.issn.2223-4683.2012.06.01. Link
- Nager CW, Brubaker L, Litman HJ, et al. A randomized trial of urodynamic testing before stress-incontinence surgery. N Engl J Med. 2012;366(21):1987-97. Link
- Ozawa H, Igarashi T, Uematsu K, Watanabe T, Kumon H. The future of urodynamics: non-invasive ultrasound videourodynamics. Int J Urol. 2010;17(3):241-9. Link
- Bianchi D, Di Santo A, Gaziev G, et al. Correlation between penile cuff test and pressure-flow study in patients candidates for trans-urethral resection of prostate. BMC Urology. 2014;14:103. doi:10.1186/1471-2490-14-103. Link
- Losco G, Keedle L, King Q. Non-invasive urodynamics predicts outcome prior to surgery for prostatic obstruction. BJU Int. 2013;112 Suppl 2:61-4. Link
- Wille S, Schumacher P, Paas J, et al. Catheterless long-term ambulatory urodynamic measurement using a novel three-device system. PLoS ONE. 2014;9(5):e96280. Link