Clinically relevant modeling of urodynamics function: the VBN model.

BACKGROUND: For the past two decades, a mathematical model of micturition was built step by step. Fundamental studies, presentations of the model and several applications to various male and female lower urinary tract dysfunctions have been published. We expect now that other teams will be interested in using it. In order to do so, a VBN pack (software in Linux and tutorial) is freely available. AIMS: The purpose of this review is to describe the model and to show its practical usefulness. MATERIALS AND METHODS: After a short description of the basis of the model and of how to use it, some published applications were summed up. The main application of the VBN model is to obtain a coherent modelling for a given patient from a set of several recordings (free uroflows and pressure-flow study) obtained either during the same session or in follow up. RESULTS: This experience gradually led us to study what information could be extracted from a free uroflow. In addition, the model is valuable to quickly compute the effect of some additional condition; thus, it can predict the effect of an experimental artefact (urethral catheter, penile cuff). CONCLUSION: Because the process of fitting model computations and real recordings is a powerful way to detect unexpected phenomena, the use of the VBN model provides a method to improve the knowledge of misunderstood dysfunctions of the lower urinary tract.

Challenging the maximum flow rate: a new index of voiding dysfunction in men with benign prostatic enlargement.

OBJECTIVES: To present the theoretical development and clinical relevance of a new index of voiding dysfunction (D) based purely on free uroflow (FF), to assist in the management of patients with benign prostatic enlargement (BPE), and to compare its merits against the maximum flow rate (Q(max)). PATIENTS AND METHODS: In the Valentini-Besson-Nelson (VBN) micturition model for men, two variables characterize urethral obstruction, i.e. the prostatic urethral counter-pressure pucp and the detrusor force coefficient k. D can be obtained from a FF assuming a normal detrusor (k = 1). Clinically, multiple FF from patients entered in a double-blind pharmacological trial provided variations of D over time. D values were also compared before and after transurethral resection of the prostate (TURP). RESULTS: In 137 patients with BPE from several institutions, D was more precise than Q(max) because D is independent of volume and of perturbations of short duration during the flow. The change in D was proportionate to the invasiveness of treatment; the mean (SD) decrease after TURP was 14.6 (8.7) cmH(2)O, vs 8.1 (5.4) cmH(2)O after 90 days of alpha-blocker intake. Retrospectively, the range of D fitted with the clinician's decision, i.e. pharmacological trial (16-31 cmH(2)O) vs TURP (27-46 cmH(2)O; P < 0.001). CONCLUSION: The new index (D), deduced from the VBN analysis of only FF, is responsive to treatment. This simple calculation offers an insight into the voiding status of a patient with BPE beyond that obtained by Q(max) alone.

Modelized analysis of pressure-flow studies of patients with lower urinary tract symptoms due to benign prostatic enlargement.

AIMS: To gain insight from an adaptable computer model of micturition into the pathophysiological phenomena occurring during voiding in men with lower urinary tract symptoms due to benign prostatic enlargement (BPE). METHODS: By using the Valentini-Besson-Nelson (VBN) micturition model, we proceeded with an in-depth and systematic analysis of the pressure-flow studies of 71 patients (119 tracings) provided by three different institutions. RESULTS: The modelized analysis identified and quantified several pathophysiological phenomena during voiding: compressive obstruction, variations in detrusor contraction force (enhanced or reduced), progressive relaxation of the prostatic fossa, occasional detrusor-bladder neck coupling, and sphincteric control dysfunctions. Once these phenomena were taken into account by using a set of new parameters, the computed flow rate and detrusor pressure curves became very similar to the recorded ones. CONCLUSIONS: The accuracy of this sophisticated analysis allows us to separate and to study during each voiding the phenomena belonging to the urethra, the detrusor, the bladder neck, the prostate, and their neurologic coordination in BPE patients.