NEW URODYNAMIC MODEL TO EXPLAIN MICTURITION DISORDERS IN BENIGN PROSTATIC HYPERPLASIA PATIENTS - PRESSURE-FLOW RELATIONSHIPS IN COLLAPSIBLE TUBES, HYDRAULIC ANALYSIS OF THE URETHRA AND EVALUATION OF URETHRAL RESISTANCE

How can the hydrodynamic disorders caused by benign prostatic hyperplasia (BPH) be explained? And how can they be measured in order to assess the efficiency of treatments? To answer these questions, a model based on the results of experiments performed in collapsable tubes and on a hydraulic analysis of the urethra is elaborated. A BPH combining hypertonia and/or hypertrophy, essentially leads to a rise in the opening pressure which increases bladder work before micturition, as well as a reduction in the functional caliber of the prostatic urethra. Whatever its origin, this reduction in caliber is the only explanation for the importance of the urethral resistance increase noticed in cases of BPH. Instantaneous resistance calculation, based on the pressure/maximum flow rate relationship, measured when the flow is steady (for a few seconds), would be a good experimental physical parameter. However, on a clinical basis, an exact calculation is impossible, which makes its precision and reliability not as good as they should be. In order to calculate the resistance to micturition as a whole, particularly taking into account the difficulty in urethral opening, it was suggested to include the opening pressure in the pressure/flow study. But this fits neither with fluid mechanics data nor with the results of experiments carried out in collapsable tubes. Eventually, considering that no evaluation method of the resistance to urinary flow is acknowledged to be accurate on a hydraulic basis or urodynamically applicable, one wonders whether placing more confidence in simple data obtained in a noninvasive way, and used without mathematical tricks, is not preferable. In this respect, maximum flow rate and voided volume seem to be the best parameters.