(1)
Functional Urology Unit, Casa Madre Fortunata Toniolo, Bologna, Italy
1.1 What Is Urodynamics?
Urodynamics is the study of the function of the lower urinary tract, e.g., bladder and urethra. More precisely it analyzes the urinary stream during voiding and pressures in the bladder and abdomen both during micturitions and in the periods between them. For these features, urodynamics disclose peculiarities that neither radiology nor endoscopy is able to process.
As in other high-technology testing procedures (e.g., electrocardiography, electroencephalography), urodynamic test have greatest clinical validity when their interpretation is left to the treating physician, who should either supervise the study or be responsible for correlating all the findings with personal clinical observations.
1.2 The Micturition Cycle
The function of the bladder is relatively straightforward: store urine to about 400–500 ml in adults and then empty voluntarily in consequence of the stimulus of voiding.
These two events, storage and emptying, are known as micturition cycle (Fig. 1.1).
Figure 1.1
The micturition cycle. As the bladder fills, relaxation of detrusor muscle allows low-pressure storage of urine. Concurrently, a crescendo increase of EMG activity maintains continence by enhancing urethral resistance. Voiding is a voluntary act associated with a lowering of urethral resistance by sphincter relaxation followed by a coordinated contraction of detrusor muscle which leads to complete emptying of the stored urine
Typically the bladder empties seven times a day and, usually, never at night.
The normal micturition last approximately 15–20 s.
While urine storage and evacuation are equally important to bladder health, it is actually the storage of urine the event more significant during everyday life.
The bladder is an organ at low pressure. That means that during the filling, its pressure does not exceed 10 cmH20. This condition allows the continuous gravitational flow of urine from the ureter to the bladder. When, for pathological reasons, the pressure in the bladder exceeds 40 cmH20, urine flow stops and accumulates in the ureters, causing along the time their dilatation.
One third of bladder filling takes place without the individual sense in it. Later on, the need to urinate becomes progressively more urgent.
The normal subject can overcome the stimulus by contracting voluntarily the external sphincter and by predisposing himself to search a bathroom to fulfill the function of emptying the bladder.
In the toilet, emptying begins with the voluntary relaxation of the external sphincter followed by the contraction of the detrusor muscle.
Storage and voiding involves complex interactions between the bladder, urethral sphincter, and nervous system. Urethral sphincter properly depends upon two elements:
The smooth muscle sphincter
The voluntary striated sphincter
In general, urinary storage is a function of the sympathetic nervous system, whereas micturition is a function of the parasympathetic nervous system. The somatic nervous system is responsible for the control of the external urinary sphincter, allowing for volitional control of the bladder function.
The basic process of micturition cycle and peripheral nervous pathways involved can be summarized as follow: (Fig. 1.2)
