Apparatus for rupturing and detecting rupturing of one of a muscle, a muscle fibre, a fibre material and a coating of a foreign material in or on a lumen, vessel or sphincter in a human or animal subject, the apparatus comprising: a balloon catheter comprising a balloon, the balloon being configured for locating in the lumen, vessel or sphincter adjacent the one of the muscle, muscle fibre, fibre material and the coating of a foreign material, an impedance planimetry measuring system located in the balloon for detecting one of the diameter of the balloon, the transverse cross-section of the balloon, the rate of change of the diameter of the balloon and the rate of change of the transverse cross-section of the balloon, and for producing a signal indicative of the one of the diameter of the balloon, the transverse cross-section of the balloon, the rate of change of the diameter of the balloon and the rate of change of the transverse cross-section of the balloon, a pump for inflating the balloon with an inflating fluid, a flow meter for measuring one of the volume and the flow rate at which the inflating fluid is being delivered to the balloon, and configured to produce a signal indicative thereof, a signal processor for monitoring the signal produced by the flow meter and the signal produced by the impedance planimetry measuring system, characterised in that: the signal processor is configured to use the monitored signals to determine rupturing of the one of the muscle, the muscle fibre, the fibre material and the coating of the foreign material in or on the lumen, vessel or sphincter in response to an inflection point in a curve representative of an increase in one of - the diameter of the balloon, - the transverse cross-section of the balloon, - the rate of increase in the diameter of the balloon, and - the rate of increase in the transverse cross-section of the balloon, each with respect to the one of the volume of the inflating fluid being delivered to the balloon and the rate of the inflating fluid being delivered to the balloon. a balloon catheter comprising a balloon, the balloon being configured for locating in the lumen, vessel or sphincter adjacent the one of the muscle, muscle fibre, fibre material and the coating of a foreign material, an impedance planimetry measuring system located in the balloon for detecting one of the diameter of the balloon, the transverse cross-section of the balloon, the rate of change of the diameter of the balloon and the rate of change of the transverse cross-section of the balloon, and for producing a signal indicative of the one of the diameter of the balloon, the transverse cross-section of the balloon, the rate of change of the diameter of the balloon and the rate of change of the transverse cross-section of the balloon, a pump for inflating the balloon with an inflating fluid, a flow meter for measuring one of the volume and the flow rate at which the inflating fluid is being delivered to the balloon, and configured to produce a signal indicative thereof, a signal processor for monitoring the signal produced by the flow meter and the signal produced by the impedance planimetry measuring system, characterised in that: the signal processor is configured to use the monitored signals to determine rupturing of the one of the muscle, the muscle fibre, the fibre material and the coating of the foreign material in or on the lumen, vessel or sphincter in response to an inflection point in a curve representative of an increase in one of - the diameter of the balloon, - the transverse cross-section of the balloon, - the rate of increase in the diameter of the balloon, and - the rate of increase in the transverse cross-section of the balloon, each with respect to the one of the volume of the inflating fluid being delivered to the balloon and the rate of the inflating fluid being delivered to the balloon. the signal processor is configured to use the monitored signals to determine rupturing of the one of the muscle, the muscle fibre, the fibre material and the coating of the foreign material in or on the lumen, vessel or sphincter in response to an inflection point in a curve representative of an increase in one of - the diameter of the balloon, - the transverse cross-section of the balloon, - the rate of increase in the diameter of the balloon, and - the rate of increase in the transverse cross-section of the balloon, - the diameter of the balloon, - the transverse cross-section of the balloon, - the rate of increase in the diameter of the balloon, and - the rate of increase in the transverse cross-section of the balloon, each with respect to the one of the volume of the inflating fluid being delivered to the balloon and the rate of the inflating fluid being delivered to the balloon.