Urodynamics

CHAPTER 15 Urodynamics

Gamal M. Ghoniem, MD, FACS

True/False: A high postvoid residual urine volume correlates with both the symptoms and urodynamic findings associated with bladder outlet obstruction (BOO).

False. A high postvoid residual volume does not necessarily mean BOO. This condition can be present in association with any physical BOO or it can be present in association with a poorly contracting bladder. Conversely, this condition may not be present in patients with severe BOO if they have enough detrusor function to overcome the outlet obstruction. Elevated postvoid residual volumes when present do not necessarily lead to infection.

A 40-year-old female with incontinence had a uroflow with Q_max of 50 mL/s, a mean of 25 mL/s, and a configuration that looks like a bread loaf standing on end. The most likely single diagnosis is?

Sphincteric incontinence with low outlet resistance.

What are the 2 events most likely to produce a similar electromyographic (EMG) pattern?

Striated sphincter dyssynergia and Valsalva voiding both produce similar EMG patterns of increased activity. Patients with these conditions void in the absence of coordination between the detrusor muscle and the external urethral sphincteric unit.

During the act of volitional voiding what would you expect a normal EMG pattern to look like?

During the act of normal volitional voiding there is increase of detrusor pressure and decrease of EMG activity.

At initiation of normal voiding, which event happens first?

The initial measurable event upon voiding is decreased EMG activity. This precedes an increase in detrusor pressure and a decrease in maximum urethral pressure.

What is the relationship between pressure and flow during normal micturition in men and women?

Normal urinary flow in young healthy males should be 15 to 25 mL/s and the associated detrusor pressure should be of less than 40 cm H₂O. Women typically void with similar or slightly higher peak flow rates, but the associated detrusor pressures are lower and usually approximately 20 cm H₂O. Interestingly, identical results on repeated measurements are difficult to obtain with repeated pressure flow studies in the same healthy individual.

What does an intermittent flow pattern in an individual with normal deep tendon and bulbocavernosus reflexes and normal perineal sensation most likely indicate?

Intermittent flow in an otherwise normal individual is most suggestive of abdominal straining. The neurologically intact patient cannot have neurogenic detrusor overactivity (NDO) or detrusor sphincter dyssynergia (DSD).

A patient with incontinence shows evidence of low compliance by urodynamics. The Valsalva leak point pressure is 20 to 30 cm H₂O. What would you tell the patient her risk of upper tract deterioration is?

Valsalva leak point pressures less than 40 cm H₂O will actually protect the upper tracts from pressure-induced hydronephrosis and subsequent deterioration in renal function. The lower the leak pressure, the less likely upper tract deterioration will happen, when bladder compliance is low.

In phase 2 (the tonus limb) of the cystometrogram, bladder compliance is most dependent upon which factor?

Viscoelastic properties of the detrusor. Other neural factors like cerebral inhibition of reflex bladder activity and intact thoracolumbar spinal cord are more active in the final phase.

What is the most important parameter in uroflowmetry with volumes between 150 and 350 mL: maximum flow rate or average flow rate?

Maximum flow rate is most indicative of normal detrusor function.

A patient, with no evidence of neurologic disease, has evidence of involuntary detrusor contractions during the filling phase of a CMG. What is your diagnosis? Idiopathic detrusor overactivity or poor compliance?

Idiopathic detrusor overactivity (IDO). In the presence of neurological disease, identical findings on a cystometrogram (CMG) would lead to the diagnosis of NDO.

What is the Valsalva leak point pressure (VLPP)?

The Valsalva leak point pressure is the pressure at which passive urethral resistance is overcome by increasing abdominal pressure during straining and urine leaks through an otherwise closed sphincter. This is not a measure of detrusor function and the result can be affected by the presence of a large cystocele.

How is detrusor pressure (P_det) calculated?

P_ves — P_abd (vesical pressure — abdominal pressure). The detrusor pressure is important in recognizing pressure increases due to abdominal and not true vesical pressure, eg, straining.

What does high bladder compliance relate to?

Bladder accommodation. High compliance does not relate to high leak pressure.

What does the static infusion urethral pressure profile most accurately predict?

Intrinsic sphincter deficiency (ISD). It does not predict striated sphincter dyssynergia or urethral obstruction.

What is the most common urodynamic findings seen in patients with cerebrovascular accident (CVA)?

Neurogenic detrusor overactivity, normal compliance, smooth sphincter synergia, and striated sphincter synergia.

True/False: In patients with cerebral infarction, the upper tracts are at minimal risk of deterioration.

True. Immediately following the injury, these patients often manifest detrusor areflexia. As they convalesce, patients with cerebral lesions (CVA, subdural hematoma, closed head injuries, brain tumors, etc) most commonly develop NDO. They can have uninhibited motor neurogenic bladders with NDO. The bladder activity in these patients is characterized as complete coordinated incontinence. These patients void at normal pressures, but in an uninhibited manner with coordination between the detrusor muscle and sphincter mechanism. In these cases, there is no detrusor sphincter dyssynergia, and high-pressure voiding is not a common finding.

When do you most likely see pseudodyssynergia?

In a patient with a CVA. In these patients, the sensation is intact.

A 72-year-old male develops urgency, frequency, and urge incontinence following a CVA. Prior to his CVA, he complained of a decreasing stream and hesitancy. His postvoid residual is 130 mL. What is the most likely cause of his high residual?