motor and the plunger of syringe 27 upwardly to rapidly withdraw the inflating fluid from balloon 13 one condition in which the microcomputer rapidly withdraws the plunger for example is when the microcomputer detects a pressure change indicative of some failure condition during the inflation phase of the procedure it should be realized that the microcomputer is capable of responding to such a failure situation much more rapidly and reliably that could a human operator of the syringe although the invention has been described heretofore with reference to the actual coronary angioplasty procedure it has equal applicability to the preliminary testing of the balloon before actual insertion into the patient it can readily be seen how the apparatus of fig1 or the apparatus of fig6 is usable to preliminarily inflate the balloon before insertion into the patient to test the patency of the balloon that apparatus or more specialized apparatus shown in fig7 may also be used to correlate the balloon pressure with the force applied by the balloon such a force pressure correlating apparatus includes a backing plate 81 upon which the balloon of the catheter under test is disposed a force sensing arm 83 is lifted by the.