Apparatus for determining the volume of gas dissolved or entrapped in transformer cooling oil includes an oil receiver, a metering space and a piston pump arranged to apply a reduced pressure to oil in the receiver and to transfer the gas which is liberated from the oil into the metering space. The piston pump is connected to and controlled by a controller. The metering space comprises a cylinder which accommodates a piston which is connected to be moved by an actuator which is connected to and controlled by the controller. The pressure detector is provided which is responsive to the pressure in the metering space and is arranged to deliver a signal indicative of the magnitude of the pressure to the controller. A transducer is connected to the controller and is arranged to produce a signal, when the said pressure reaches a predetermined value, which is indicative of the volume of gas within the metering space.

A physiological simulation device for measuring compliance conditions of a prosthesis, such as stents, grafts and stent-grafts, under simulated physiologic loading conditions. The prosthesis is positioned within a fluid conduit of the fatigue tester, wherein the fluid conduit is filled with a saline solution or other fluid approximating the physiological condition to be tested. The fluids are forced through the fluid conduit from both ends of the fluid conduit in a pulsating fashion at a high frequency, thereby simulating systolic and diastolic pressures. The temperature of the fluid is maintained at a specific (37.degree. C.) temperature via a closed loop PID control system. The fluids are pulsated by a pulse generation system consisting of a voice coil drive motor connected to a bellows assembly. Use of a linear drive motor increases the number of cycles per minute to which the prosthesis may be subjected. A microprocessor-based controller operates the pulse generation system at a frequency ranging from 0 to over 6000 cycles/minute under closed loop control. The microprocessor-based controller may be servo controlled, utilizing feedback from a compliance transducer system, linear displacement transducer, and pressure transducer.

A vascular prosthesis tester (10) for inducing stresses upon a vascular prosthesis (22) having a channel extending through the vascular prosthesis is disclosed. The tester includes a pump (18) adaptable to pressurize a fluid disposed within the channel to induce a radial stress upon the vascular prosthesis. The tester may further include a bend applicator (16) operable to induce a bending stress, a torque applicator (12) operable to induce a torque, a linear force applicator (52) operable to induce a linear force, and/or a stop (28) for inducing a lateral push stress upon the vascular prosthesis. A method of fatigue testing a vascular prosthesis contained within a fluid conduit is also disclosed. The method includes injecting a fluid within the inner channel and inducing a torque, bending stress, linear stress, and/or later push stress upon the vascular prosthesis.

Systems and methods for fatigue testing one or more stents based on measured electrical resistance levels of each stent. Pairs of lead lines from an ohmmeter are connected to a respective stent. The respective stent is mounted onto an expander having an interior tapered portion into which a correspondingly tapered expansion pin is received. Cyclic loading strains are applied to the respective stent as an expansion pin is inserted into a corresponding one of the expanders. Stent fracture or failure occurs when cyclic loading exceeds the stents architectural and material capacity. Such fracture fatigue or failure is identified by increased electrical resistance levels. Resistance may be continuously monitored to more readily identify the onset of fatigue or failure. The expansion pins extend from a movable plate, and the expanders comprise a part of corresponding stations that extend from a fixed plate.

A vascular prosthesis tester (10) for inducing stresses upon a vascular prosthesis (22) having a channel extending through the vascular prosthesis is disclosed. The tester includes a pump (18) adaptable to pressurize a fluid disposed within the channel to induce a radial stress upon the vascular prosthesis. The tester may further include a bend applicator (16) operable to induce a bending stress, a torque applicator (12) operable to induce a torque, a linear force applicator (52) operable to induce a linear force, and/or a stop (28) for inducing a lateral push stress upon the vascular prosthesis. A method of fatigue testing a vascular prosthesis contained within a fluid conduit is also disclosed. The method includes injecting a fluid within the inner channel and inducing a torque, bending stress, linear stress, and/or later push stress upon the vascular prosthesis.