Interpretation of Urodynamic Studies: A Case Study-Based Guide

By Seung-June Oh

This book is a comprehensive guide to lower urinary tract dysfunction that draws extensively on actual urodynamic traces and patient cases to ensure that the imparted knowledge will be readily transferable to clinical practice. The impressive collection of clinical cases is used to illustrate basic concepts of lower urinary tract function and to document urodynamic findings and typical patterns in a wide range of commonly encountered conditions. In addition, attention is drawn to frequent pitfalls and artifacts. Readers will be able to assess their skill in reaching the correct diagnostic conclusion in each case, as in addition to the urodynamic trace a full set of information is provided on aspects such as patient history, physical examination, voiding diary, laboratory examination, imaging studies, and cystourethroscopy, thereby directly simulating real-life clinical practice. The presented cases are drawn from the large clinical database that Professor Seung-June Oh has prospectively accumulated during the past 16 years of clinical practice. The book will be invaluable for residents and other practitioners and will also be of interest for medical students.

• Language: English
• Publisher: Springer
• Release date: Jun 8, 2018
• ISBN: 9789811022845

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Part ITen-Minute Neurophysiology and Overview of Urodynamic Study

© Springer Science+Business Media Singapore 2018

Seung-June OhInterpretation of Urodynamic Studies https://doi.org/10.1007/978-981-10-2284-5_1

1. Ten-Minute Neurophysiology

Seung-June Oh¹ 

(1)

Department of Urology, Seoul National University Hospital, Seoul, South Korea

Before jumping into the diagnosis of patients with lower urinary tract dysfunction, let us briefly overview the basic neurophysiology in an easy way.

1.1 Step 1: Urinary Bladder/Urethral Sphincter

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First, let us go over the end organs responsible for micturition: the bladder and the urethral sphincter.

The fundamental end organs responsible for storage and voiding are the urinary bladder and urethral sphincters. The bladder continuously receives and stores urine produced by the kidneys. In addition to these, the pelvic floor muscles surround the urethral sphincter. The pelvic floor muscles are a group of muscles that are mobilized when you voluntarily contract the anus.

The bladder, urethral sphincter, and pelvic floor muscles are under neural control. Though somewhat controversial, the urethral sphincter and pelvic floor muscles are known to be somatically innervated by the pudendal nerve.

1.2 Step 2: Overview of Micturition Center and Nuclei Related to Storage and Voiding

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Let us briefly overview the basic micturition center and nuclei involved with storage and emptying.

There are two nuclei located in the S2–S4 sacral spinal cord. The most important nucleus is parasympathetic nervous system responsible for bladder contraction and the other nucleus is somatic nervous system responsible for the striated urethral sphincter. Both the bladder and the urethral sphincter will contract if stimulated.

The nucleus (sympathetic nervous system) responsible for urine storage is located in the thoracolumbar spinal cord. If stimulated, the bladder body will relax, and the bladder neck or the proximal sphincter will contract.

Further above, there is an important micturition center located in the pons. This sends signals to the three nuclei mentioned above to contract the bladder and to relax the sphincter.

At the uppermost level lies the cerebral cortex, which sends signals to inhibit bladder contraction.

1.3 Step 3: Bladder/Sphincter

The most fundamental primary neural control center responsible for voiding is located in the sacral spinal cord.

If the urinary bladder is not full, the urinary bladder sends a low-level afferent signal to the sympathetic nervous system for active relaxation of the bladder and contraction of the proximal smooth sphincter to store urine. At the same time, the signal also stimulates somatic nervous system to maintain distal striated sphincter closed (Also refer to the Sect. 1.7).

When the bladder is full, the bladder sends an intense afferent signal to the pons. The pons, in turn, sends signals to the sympathetic nervous system to terminate both bladder relaxation and proximal sphincter contraction. Primary micturition center is activated by the pons: somatic nervous system receives signal from pons to stop distal striated sphincter contraction, and the parasympathetic nervous system is activated to contract the bladder smooth muscle to empty the bladder (Also refer to the Sect. 1.8).

This is the basic nervous control mechanism of the contraction and relaxation of the bladder.

1.4 Step 4: Bladder/Sphincter and Pontine Micturition Center

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The main control tower for both bladder and urethral sphincters exists in the pons (pontine micturition center, PMC), which sits above the spinal cord.

When the PMC is stimulated by the bladder-filling sensation, the PMC sends a signal to the sympathetic nervous system to stop bladder relaxation and also sends a signal to relax the urethral sphincters as mentioned before. At the same time, the PMC sends a signal to the primary sacral micturition center to contract the bladder smooth muscle. In other words, the PMC simultaneously makes the bladder contract and the urethral sphincter relax. The PMC coordinates the bladder (contraction) and the urethral sphincter (relaxation) to empty the bladder.

We have now covered the very basic coordination of the storage and emptying of urine: how the sphincter contracts when the bladder is relaxed to allow for storage, and how the sphincter relaxes when the bladder contracts to allow for emptying.

1.5 Step 5: Bladder/Sphincter, Pontine Micturition Center and Cerebral Cortex

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The higher control system above the pons allows for a more refined control of the basic micturition mechanism that was previously mentioned. The higher order function is found in evolved species that possess advanced cerebral hemispheres required for socialization.

For example, if one is in the middle of a conference and feels an urgency to use the restroom, one must be able to defer micturition until an appropriate timing arises. The cerebral cortex allows for such control.

By default, the cerebral hemispheres function to inhibit the contraction of the bladder. Very young infants urinate whenever they need to because their brains are not yet mature enough to have the social control of urination. This also explains why one’s ability to control over the bladder drops with aging or neurodegenerative diseases, which cause an overall functional decline of the nervous system.

To summarize, the storage of urine is sympathetic nervous system dominant, and the emptying of urine is parasympathetic nervous system dominant.

1.6 Local Reflex Circuits

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Also, there are a number of local neural circuits that act independently. For example, when one feels desire to void, he or she can consciously contract the pelvic floor muscle in order to prevent the contraction of the bladder (guarding reflex). This is a local reflex arc by which one can temporarily eliminate the bladder contraction.

1.7 Storage Phase Mechanism

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The followings are review of the above information according to storage and voiding phase. Interestingly, nervous systems are also activated during storage phase as well as the voiding phase.

During the storage phase, low-level bladder afferent firing does not travel to higher center, but it stays within spinal level. It stimulates (1) sympathetic outflow to contract bladder neck and actively relax bladder body. In addition, it also stimulates (2) pudendal outflow of somatic nerve to close distal striated sphincter.

1.8 Voiding Phase Mechanism

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During the voiding phase, an intense afferent activity from the bladder directly travels to pontine micturition center (PMC).

The PMC inhibits both sympathetic outflow and somatic outflow. In addition, the PMC stimulates parasympathetic outflow to contract detrusor muscle.

1.9 Pathologic Conditions

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Now let us take a look at some pathologic conditions. If the bladder itself is directly damaged by trauma or if the detrusor muscle is destroyed by severe infection such as bladder tuberculosis, the normal storage and emptying of urine will be affected. If the proximal urethra is obstructed as in benign prostatic hyperplasia (BPH), the emptying of urine will be primarily affected.

What if the lesion exists at the level of sacral spinal cord, the primary neural control center? The basic voiding function will be impaired.

What if the lesion exists somewhere between the primary (sacral spinal cord) and secondary (pons) micturition centers? Spinal cord injury caused by a motor vehicle accident will be a typical example. In this case, two phenomena will be observed: firstly, the coordination between the bladder and the urethral sphincter will be lost such that they simultaneously contract; secondly, the inhibitory signal from the cerebral cortex will not be able to reach the bladder. In short, the harmonious emptying of urine becomes impossible because the urethral sphincter cannot relax when the bladder contracts and the detrusor overactivity cannot be inhibited.

What if the lesion exists between the secondary neural control center (pons) and the cerebral cortex? It will be extremely difficult to hold urine in the bladder because, as mentioned above, the overactivity of the bladder cannot be suppressed. This explains why Parkinson’s disease or stroke patients are unable to hold in urine even with a slight filling of the bladder.

1.10 Summary

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We have briefly covered the mechanisms governing lower urinary tract function thus far. Let us now sum up everything once again.

In order for voiding to take place harmoniously, the bladder and the urethral sphincter must be intact.

The primary control center is located in the sacral spinal cord; it is responsible for the primary contraction of the bladder when the bladder is full. The secondary control center is in the pons; it is responsible for the coordinated control of the bladder (detrusor muscle) and the urethral sphincter such that the bladder contracts, while the urethral sphincter relaxes. The cerebral hemispheres appropriately control the detrusor muscle as needed. The SNS relaxes the bladder while contracting the bladder neck during the storage phase.

The relationship between the bladder/urethral sphincter and the nervous system can be compared to that between the horse and the rider; the nervous system being the rider and the bladder/urethral sphincter being the horse. Both the rider and the horse must be in good condition to reach the destination in time. With both or either one of the two being not intact, we cannot expect to reach the destination.

© Springer Science+Business Media Singapore 2018

Seung-June OhInterpretation of Urodynamic Studies https://doi.org/10.1007/978-981-10-2284-5_2

2. Overview of Urodynamic Study

Seung-June Oh¹ 

(1)

Department of Urology, Seoul National University Hospital, Seoul, South Korea

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2.1 Turning Pressure and Flow into a Signal

Lower urinary tract symptoms (LUTS), such as urinary leakage or voiding difficulty, are often encountered in everyday life. The storage and excretion of urine is one of the most fundamental physiological activities necessary for the maintenance of life. This process is a part of the lifelong body activities of living individual.

The inability to store or empty urine appropriately undermines one’s quality of social life. Patients that are incapable of appropriate emptying of urine may have their kidneys damaged. Some patients with urinary leakage also complain about how wearing diapers all day negatively impact their social lives. All of these are problems caused by lower urinary tract dysfunction.

The problem of storing and emptying urine is very closely related to the fluid pressure. The fluid naturally flows from a point of high pressure to a point of low pressure. By harnessing bodily mechanisms, the bladder and the urethra can set up a high pressure, or sometimes a low pressure, for the fluid. With appropriate control of the pressure applied, the fluid would always flow toward the point of lower pressure, namely, the outside. If an excessively high pressure is set up, the urine may leak. If an excessively low pressure is set up, the urine would not be emptied. The bladder and the urethral sphincter work in order to set up a proper pressure gradient, and the nervous system governs and controls this process.

All the lower urinary tract dysfunctions are related to ‘pressure.’ We must therefore have a clear understanding of the biologic phenomenon by which the pressure is set up. We are certain that the proper and exact measurement of established pressure is the most important and accurate method in approaching and diagnosing patients with lower urinary tract dysfunction. The urodynamic study (UDS) is such a method. In this book, it is our aim to guide you through the diagnostics using the UDS in the most efficient and straightforward manner.

2.2 Step 1: Pves Measurement

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In order to measure in vivo function of the lower urinary tract, we need a device to measure the pressure of the bladder (Pves) and the urethra.

In the diagram, you can see a catheter, inserted to measure the bladder pressure. International Continence Society (ICS) standard urodynamic study is performed with the thinnest possible (6 Fr) transurethral triple (or double) lumen catheter (Schäfer et al. 2002; Rosier et al.