How does physiological pressure/compliance (also know as load control) testing differ from strain control testing?
Physiological pressure/compliance testing simulates what is happening in vivo. This technique had been shown to produce breakage and fractures in the same place and at a similar number of cycles as in clinical trials. Strain control testing, although usually carried out at higher frequencies, has not been shown to correlate with clinical results. The new ASTM standards will require verification that the outside of the stent follows the inside of the tube throughout the cycle. One method of verifying “vessel motion” is to measure the outside wall of the vessel and calculate the “inner motion”. The problem with outside diameter measurements arises from two different sources. First, when a viscoelastic tube is pressurized and increases in diameter, the wall must thin out in order to circumscribe a larger diameter. This thinning of the wall means that the change in the inside diameter of the tube is never the same as the change in the outside diameter of the tube. If the tube has any poros
