Since the establishment of miniaturized extracorporeal circulation (mECC), there has been a great controversy about a possible increased risk of gaseous microembolism as compared to conventional extracorporeal circulation (cECC). From March 2005 to June 2006, a prospective, randomized study, comparing three different mECC (MECC, PRECiSe, Resting Heart) with a cECC (HL30 Maquet) was performed. Ninety-three patients undergoing elective bypass surgery were included. The amount and size of microbubbles during perfusion was detected in the arterial lines utilizing an ultrasound Doppler system. Clinical outcome was compared by evaluating the incidence of postoperative neuropsychological dysfunction, postoperative renal dysfunction and hospitalization as well as the 30-day mortality. The highest microbubble activity was measured in all devices during the first 10 minutes of extracorporeal circulation. The amount of microbubbles was lower in the Resting Heart system (p=0.01), equal in the MECC system (p=0.16) and higher using the PRECiSe system as compared to the cECC (p=0.002). The microbubble diameter did not differ between all groups (p=0.56). Postoperative neuropsychological dysfunction (p=0.45), renal dysfunction (p=0.67), days of hospitalization (p=0.27), and 30 day-mortality (p=0.30) did not differ between all groups. A great variability in the occurrence of gaseous microemboli depending on the applied circuit exists. The Resting Heart system has lower, the MECC system an equal and the PRECiSe system depicted a higher activity in comparison to a cECC. The hypothesis about an increased risk in mECC in comparison to cECC with regard to microbubble activity is not supported by our results.
Zusammenfassung Bereits 1604 soil der Arzt Cabriolanus caber geheilte bzw. heilende Herzwunden bei einer Autopsie berichtet haben. Die eigentlichen Anfange der Herzchirurgie sind jedoch wohl eher in das Ende des 19. Jahrhunderts zu legen, als der Chefarzt der Abteilung fur Chirurgie der Stadtischen Kliniken in Frankfurt am Main, Ludwig Rehn (1849-1930), am 9. September 1896 -dem Jahr, in dem Scipione Riva-Rocci (1863-1937) seine einfache Methode der unblutigen Blutdruckmessung beschrieb -die erste erfolgreiche Naht einer Stichverletzung des Herzens gelang. Er legte Ober eine linksseitige Thorakotomie drei Nahte mit einer Darmnaht und Seide caber eine blutende Stichwunde im rechten Ventrikel eines 22-jahrigen Mannes, dessen Leben durch diese Operation gerettet werden konnte [157, 158]. Zuvor waren von Roberts in den USA (1881), Farina in Rom (Marz 1896) und Cappelen in Christiana in Oslo (5. September 1894) gleichartige Operationen ohne Erfolg durchgefuhrt worden. Von erfolgreichen Herznahten an Versuchstieren hatten allerdings bereits 1882 Block [24] bei Kaninchen und 1885 del Vecchio bei Hunden berichtet, wahrend Fischer sogar bereits 1868 im Archiv fur klinische Chirurgie eine Arbeit caber Die Wunden des Herzens und des Herzbeutels publizierte [71].
Advances in additive manufacturing enable the production of tailored lattice structures and thus, in principle, coronary stents. This study investigates the effects of process-related irregularities, heat and surface treatment on the morphology, mechanical response, and expansion behavior of 316L stainless steel stents produced by laser powder bed fusion and provides a methodological approach for their numerical evaluation. A combined experimental and computational framework is used, based on both actual and computationally reconstructed laser powder bed fused stents. Process-related morphological deviations between the as-designed and actual laser powder bed fused stents were observed, resulting in a diameter increase by a factor of 2-2.6 for the stents without surface treatment and 1.3-2 for the electropolished stent compared to the as-designed stent. Thus, due to the increased geometrically induced stiffness, the laser powder bed fused stents in the as-built (7.11 ± 0.63 N) or the heat treated condition (5.87 ± 0.49 N) showed increased radial forces when compressed between two plates. After electropolishing, the heat treated stents exhibited radial forces (2.38 ± 0.23 N) comparable to conventional metallic stents. The laser powder bed fused stents were further affected by the size effect, resulting in a reduced yield strength by 41% in the as-built and by 59% in the heat treated condition compared to the bulk material obtained from tensile tests. The presented numerical approach was successful in predicting the macroscopic mechanical response of the stents under compression. During deformation, increased stiffness and local stress concentration were observed within the laser powder bed fused stents. Subsequent numerical expansion analysis of the derived stent models within a previously verified numerical model of stent expansion showed that electropolished and heat treated laser powder bed fused stents can exhibit comparable expansion behavior to conventional stents. The findings from this work motivate future experimental/numerical studies to quantify threshold values of critical geometric irregularities, which could be used to establish design guidelines for laser powder bed fused stents/lattice structures.
