Chapter 29

Urodynamic study is an important part of the evaluation of patients with lower urinary tract obstruction, voiding dysfunctions, urinary incontinence, and neuropathic disorders involving the lower urinary tract. Formerly, the examiner simply observed the act of voiding, noting the strength of the urinary stream, and drawing inferences about the possibility of obstruction of the bladder outlet. In the 1950s, it became possible to observe the lower urinary tract by fluoroscopy during the act of voiding, and in the 1960s, the principles of hydrodynamics were applied to lower urinary tract physiology. In the 1970s, videourodynamic was introduced, where fluoroscopy was incorporated with the pressure measurements to adequately assess both anatomy and function.

The field of urodynamic now has clinical applications in evaluating voiding problems resulting from lower urinary tract disease.

The nomenclature of the tests used in urodynamic studies is not yet settled, and the meanings of urodynamic terms are sometimes overlapping or confusing. In spite of these difficulties, urodynamic tests are extremely valuable. Symptoms elicited by the history or by physical, endoscopic, or even radiographic examination usually delineate the anatomic findings, but the function often must be investigated further by urodynamic tests so that therapy can be devised that is based on an understanding of the altered physiology of the lower urinary tract.

As is true of many high-technology testing procedures (eg, electrocardiography, electroencephalography), urodynamic tests have the greatest clinical validity when their interpretation is left to the treating physician, who should either perform or closely supervise the study or be responsible for correlating all of the findings with personal clinical observations.

Urodynamic studies in concert with an accurate history and physical examination are the most useful clinical tools available for the evaluation of the lower urinary tract and can provide useful clinical information about the function of the urinary bladder, the sphincteric mechanism, and the voiding pattern itself.

Bladder function. This can be evaluated by simple cystometrogram (CMG) that measures vesical pressure as a function of bladder volume. This can provide important information on cystometric bladder capacity, bladder sensation, bladder compliance, and the presence of involuntary bladder contraction and bladder contractility.

Sphincteric function depends on two elements: the smooth muscle sphincter and the voluntary sphincter. The activity of both elements can be recorded urodynamically by measuring urethral pressure profile or by recording sphincter electromyography.

The act of voiding is a function of the interaction between bladder and sphincter, and the result is the flow rate. The flow rate is one major aspect of the total function of the lower urinary tract. It is generally recorded in milliliters per second as well as by total urine volume voided. The simultaneous recording of bladder activity (by intraluminal pressure measurements), sphincteric activity (by electromyography or intraluminal urethral pressure measurements), and flow rate reveals interrelationships among the three elements. Each measurement may give useful information about the normality ...

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