Urogenital re-education by electrostimulation: modelling for minimum energy computation

The analysis of the voltage curve V(t) picked up between the two electrodes of a vaginal plug used with a current source stimulation allowed us to suggest a simple electrical model for intravaginal tissue. It is made up of three cells in series: a resistor in parallel with a capacitor for the first two, and a simple resistor for the third. Measurements throughout the hormonal cycle exhibit large variations in resistance and capacitance, and justify the use of a current source device to keep reproducible conditions of stimulation. Subjective detection of sensitivity threshold currents shows results which are independent of the day in the cycle and thus confirms the use of current source stimulation. The curve representing dissipated energy as a function of the pulse duration tau exhibits a minimum value different from the chronaxie (here 800 microseconds). The minimum value is effectively obtained at lower values of tau between 450 and 500 microseconds, dependent on the day of the cycle and the electrical characteristics of vaginal tissue. Two values of tau (230 and 1000 microseconds) between which the energy dissipated is less than Emin + 10 per cent are determined. This gap of pulse duration seems to be a correct range according to the minimum energy criterion for electrostimulation applied to urogenital re-education.