Holographic interferometry for in vitro investigations of prosthetic heart valves

In prosthetic heart valve replacement the possibility of valve dysfunction is of particular importance. Preoperative nondestructive testing of each individual valve could prevent the implantation of valves that are potentially dysfunctional owing to material failure. For that purpose holographic interferometry as a noncontacting, nondestructive, highly sensitive, three-dimensional measurement technique has been applied. Samples of seven different types of prosthetic heart valves (Wada-Cutter, Cross-Jones, Björk-Shiley, Omnicarbon, Lillehei-Kaster, Starr-Edwards, and St. Jude-Medical) were investigated in our experiments. The valve under investigation was mounted in a specially developed liquid-filled test chamber, which provided optical access to the valve from four sides, and was stressed in closed position at the physiological level of loading. Deformations of the valve due to a small pressure difference applied between exposures were recorded by double-exposure holography. A fringe pattern superimposed on the image of the valve reconstructed from the hologram clearly indicates—with the sensitivity and accuracy of a fraction of the laser wavelength used—the presence of any slightest defect in the valve material. The series of experiments carried out with different valves has demonstrated that this fringe pattern is reproducible and that its shape is specific for each type of valve. Deviations of these shapes from the typical ones point out the weaknesses and hidden defects, which could be responsible for dysfunction of the valves, a high level of hemolysis, or other functional disorders.