BHV LEAFLET STRAIN MONITORED BY DOUBLE-PULSE STEREO-PHOTOGRAMMETRY

The short life span of current bioprosthetic heart valves (BHVs) remains to be a major concern. It is believed that the valve failure is directly related to the uneven stress distribution within the valve leaflets. Current in vitro study of the stress distributions using experimental assessment or theoretical modeling was conducted based on measured material properties from dissected valve leaflet. However, the surface stress-strain within the intact valve leaflet under physiologic conditions has not been reported. This information is crucial for realistic stress-strain analysis. To address this problem, a stereophotogrammetry system with two simultaneous cameras was developed to assess the surface strain of the valve leaflet. The experiment was conducted inside a pulse flow loop (PFL) that closely simulates the physiologic conditions. A pericardial valve was installed in the aortic valve position of the PFL with one of the leaflet marked with approximately 125 India Ink dots forming a marker matrix for detailed strain analysis. A high speed stroboscope was employed as the illumination device, which was triggered by a double-pulse train to capture sequence of dual pictures corresponding to consecutive leaflet images before and after the deformation in a fixed minimum duration of 4.5 mu s. The local leaflet surface strain was calculated directly using the marker's coordinates in the consecutive images. By using this technique, sequence of strain maps corresponding to various phases of leaflet motion was obtained for the complete cardiac cycle.