[Accuracy of pressure measurements obtained with a new rectal balloon catheter]. / Exactitude des mesures de pression obtenues par une nouvelle sonde rectale à ballonnet à air.

UNLABELLED: The accuracy of measurements performed by a balloon catheter used to record abdominal pressure during urodynamic investigations was verified on a test bench. OBJECTIVE: To study the accuracy and precision of the pressure measurements obtained with a new rectal balloon catheter (ref. 95018 Laboratoires Vermed), designed to record abdominal pressure during urodynamic assessments. The clinical value of this catheter, using air for pressure transmission, is its simplicity, as there is no contamination of the perfusion circuit or transducer, no purging of the circuit, and artefacts related to movements of the tubing are eliminated. METHOD: The catheter was placed in a pressure chamber fitted with a precise, calibrated regulation system allowing programmed pressure variations from 10 to 150 cmH2O. Pressures recorded by the test catheter were compared to reference pressures applied to the chamber. The frequency of acquisition of pressure measurements was 100 Hertz and the resolution was 10 Hertz. This model was used to study the accuracy of pressure measurements and the response times of the catheter. Measurements were performed with a volume of 2 ml of air introduced into the catheter (volume recommended by the manufacturer), and the optimal volume was investigated by inflating the catheter until the best result was obtained. The evaluation was based on calculation of the mean difference observed between the two measurements and the scatter of the differences observed. RESULTS: When the catheter was filled with 2 ml of air, pressures measured by the catheter were overestimated an average of 1.1 cmH2O (standard deviation = 1), and 95% of the differences between the two measurements were within +/- 2.15 cmH2O. The optimal air volume was found to be 1.5 ml. With this air volume, no significant difference was observed between the two measurements. The mean observed difference was 0.2 cmH2O (SD = 1.2), which means that 95% of the differences were situated within the range of +/- 2.35 cmH2O. CONCLUSION: The pressure recording method with this new catheter is validated in terms of physical parameters.

[Instantaneous pressure/flow ratio for non-permanent flows. Impact on the assessment of urethral resistance]. / Relation pression/débit instantanée pour des flux non permanents. Conséquences sur l'évaluation de la résistance uréthrale.

OBJECTIVE: To verify the validity of the hypothesis of the almost continuous flow necessary for evaluation of instantaneous urethral resistance R by the pressure/flow relation R = P/Q2. METHOD: An experimental device allowed investigation of the pressure/flow relation for discontinuous flow in a flexible tube. The tube was submitted to various collapsing pressures and opened under the effect of flow. The flow was discontinuous because of the variations of the proximal pressure or oscillations in the hydraulic diameter of the tube. RESULTS: These experiments showed that the approximation of continuous flow is justified within the limits of precision of the measuring methods used in urodynamics. CONCLUSION: The formula R = Q2 is therefore theoretically correct and validated by the experimentation. There is no hydrodynamic obstacle to the application of this formula to the calculation of instantaneous urethral resistance.

[Reliability of pressure measures determined with probes used for establishing the urethral pressure profile by the perfusion method]. / Fiabilité des measures de pressions obtenues par les sondes utilisées pour la réalisation du profil de pression uréthral par la méthode perfusionnelle.

The objective of this study was to evaluate the reliability of pressure measurements by the main catheters used to determine urethral profiles by the perfusion method. This evaluation, performed on a test bench, compared the reference pressure in a tank filled with water to that measured by the catheter tested. The reliability of the measurement varied from one catheter to another. This disparity was due to differences of load losses, leading to an overestimation of the measurement (by 2 to 17 centimetres of water), which must be corrected by adjustment of the zero pressure with a perfused catheter. Major differences in the rapidity of response (from zero to five seconds) were also observed, which appear to be related to elastic properties of the catheter. This study does not pretend to globally verify the reliability of the perfusion method, but only the reliability of pressure measurements.

[Incidence of the form and caliber of urethral resistance. Evaluation for a normal masculine urethra and in cases of obstruction due to prostatic hypertrophy]. / Incidence de la forme et du calibre dans la résistance uréthrale. Evaluation pour un urèthre masculin normal et en cas d'obstruction par hypertrophie de prostate.

Certain forms of benign prostatic hypertrophy are associated with a reduction of the calibre of the prostatic urethra of the median lobe, a defect of infundibulisation of the bladder neck and a dilated appearance of the bulbar urethra. The objective of this study was to verify whether hydrodynamic arguments could be used to confirm the concept that defective infundibulisation of the bladder neck is directly responsible for an obstructive syndrome or via a reduction in the calibre of the bladder neck orifice. More generally, this study was designed to quantify the distribution of resistance to flow along the normal urethra and to define the role of cervicoprostatic and urethral deformities in the obstruction associated with benign prostatic hypertrophy. Urodynamic studies are unable to answer this question, as the instantaneous urethral resistance is evaluated globally by the Pressure-Flow relation. The authors performed morphological analysis to divide the urethra into simple hydraulic segments for which the corresponding pressure drop coefficients were calculated. These coefficients constitute an approach to segmental resistance to flow and can be used to quantify changes in shape observed on voiding urethrography or ultrasonography. Digital analysis of voiding urethrographies showed that, under normal conditions, urethral resistance was regularly distributed along the urethra and essentially depended on friction of the urethral wall. In the case of benign prostatic hypertrophy, even with a median lobe, the increase in the pressure drop coefficients was due to a reduction in the calibre of the bladder neck orifice and prostatic urethra. Cervical deformities appeared to be minimally obstructive, according to urodynamic parameters, if they were not associated with a reduction in the calibre of the bladder neck orifice.

[Instantaneous pressure-flow relations in a continuous flow in a collapsible tube: impact on the evaluation of urethral resistance]. / Relation pression-débit instantanée en flux permanent dans un tube collabable: conséquences sur l'évaluation de la résistance uréthrale.

The urethra is a collapsed tube in the absence of micturition. Consequently, the evaluation of instantaneous urethral resistance by the pressure/flow relation (R = P/Q2) derived from Bernoulli's equation has been criticised for not taking into account the opening pressure or at least the fact that flow must maintain patency of the urethra during voiding. The objective of this study was to determine whether such a criticism is justified in terms of fluid mechanics. A study of the pressure/flow relation was performed in a soft tube, collapsed by various peritubular pressures, which subsequently opened in response to flow. Experiments demonstrated that the pressure/flow relation, the instantaneous resistance to flow and the pressure drop were identical when the tube reached the same calibre, despite different peritubular pressures. The same pressure therefore propels the flow and maintains the patency of the tube. Consequently, it would be unreasonable to expect to improve the evaluation of instantaneous urethral resistance by subtracting an opening pressure from the maximal bladder pressure. The formula R = P/Q2 is valid, experimentally, and complies with the principles of fluid mechanics. In theory and in practice, it constitutes a good method of evaluation of instantaneous resistance.

New urodynamic model to explain micturition disorders in benign prostatic hyperplasia patients. Pressure-flow relationships in collapsable 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 treatment? 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.(ABSTRACT TRUNCATED AT 250 WORDS)

Drug addicts attending specialised institutions: towards a drug addiction data bank?

In 1986, a national survey was carried out in France among 4846 drug abusers attending specialised agencies and treatment centres. Data are analysed and compared with the results of a previous study in 1972. Most French drug abusers are men (74%) ranged in age from 20 to 29 years (68%). Data suggest increasing problems with heroin (69%), cocaine (13%), solvents (5%), alcohol (26%) and multiple drug dependence. Women are younger, they have attempted suicide more often than men but have been incarcerated half as often. Concerning drug abuse trends, women appear to use increasingly sedatives in combination with other drugs. Partial data concerning HIV seropositivity reveal a rate of 48% among drug abusers having been tested.

[Urodynamic consequences of urethral stenosis. Hydrodynamic study with a theoretical model]. / Retentissement urodynamique d'un rétrécissement urétral. Etude hydrodynamique d'un modèle théorique.

An urethral model was designed to assess the hydrodynamic consequences of stenosis of the bulbar urethra. This model was based on the geometric and hydrodynamic analysis of micturing urethrograms in a patient whose maximum flow rate was 24 ml/s for a bladder pressure of 40 cm of water. It corresponds to the conditions of flow observed wit maximum bladder pressure and flow rate. During this short period, the shape of the urethra is regarded as stable. Calculation took account of the characteristics of a turbulent flow of urine, of the head loss due to friction of the urine on the walls and of the head loss caused by the geometrical changes of the urethra from the neck of the bladder to the meatus. In these conditions, applying Bernouilli's equation allowed plotting of bladder pressure for various levels of urethral resistance. If there is no stenosis, the theoretical maximum flow rate of the model with a bladder pressure of 40 to 80 cm of water should be 19 to 26 ml/s. Calculation showed that a sudden reduction of the diameter to less than 2.5 mm occurring in a segment of the urethra with a diameter of 4 mm accounts for a flox rate lower than 15 ml/s, except when bladder pressure can exceed 100 cm of water. The decrease in the maximum flow rate caused by urethral stenosis is all the greater as bladder pressure remains low or normal, with other causes of head loss or with associated upstream dilatation. Lastly, progressive narrowing leads to a smaller head loss and will therefore be better tolerated than sudden narrowing to the same caliber. Inversely, a long stenosis will be less well tolerated as the head loss due to friction in a long and narrow passage is increased. The diameter of a stenosis accounting for a maximum flow rate of less than 15 ml/s cannot be determined in the absolute. Analyzing the hydrodynamic consequences of stenosis also requires knowing the associated urodynamic and geometric parameters.