To make an analysis of the usefulness of urodynamic tests and what can be obtained from them.We also perform and analytical deduction of those parameters that define detrusor behavior, such as the constant defining bladder compliance, the bladder elastic constant, in its tensile properties, and we found the expression of resistances and calculate the abdominal pressure formula; therefore we don't need to introduce a rectal catheter to know the value of those parameters that define bladder dynamics.Although they are provisional, they allow foreseeing a promising future for this application of a well-known device.Currently, we can only define the bladder behaviour, its resistances, the detrusor drive and compliance with the only discomfort of a perineal Doppler ultrasound. Time will open new possibilities.