Reinforcing the pulmonary artery autograft in the aortic position with a textile mesh: a histological evaluation

OBJECTIVES The Ross procedure involves replacing a patient’s diseased aortic valve with their own pulmonary valve. The most common failure mode is dilatation of the autograft. Various strategies to reinforce the autograft have been proposed. Personalized external aortic root support has been shown to be effective in stabilizing the aortic root in Marfan patients. In this study, the use of a similar external mesh to support a pulmonary artery autograft was evaluated. METHODS The pulmonary artery was translocated as an interposition autograft in the descending thoracic aortas of 10 sheep. The autograft was reinforced with a polyethylene terephthalate mesh (n = 7) or left unreinforced (n = 3). After 6 months, a computed tomography scan was taken, and the descending aorta was excised and histologically examined using the haematoxylin–eosin and Elastica van Gieson stains. RESULTS The autograft/aortic diameter ratio was 1.59 in the unreinforced group but much less in the reinforced group (1.11) (P < 0.05). A fibrotic sheet, variable in thickness and containing fibroblasts, neovessels and foreign body giant cells, was incorporated in the mesh. Histological examination of the reinforced autograft and the adjacent aorta revealed thinning of the vessel wall due to atrophy of the smooth muscle cells. Potential spaces between the vessel wall and the mesh were filled with oedema. CONCLUSIONS Reinforcing an interposition pulmonary autograft in the descending aorta with a macroporous mesh showed promising results in limiting autograft dilatation in this sheep model. Histological evaluation revealed atrophy of the smooth muscle cell and consequently thinning of the vessel wall within the mesh support

Biomechanical evaluation of a personalized external aortic root support applied in the Ross procedure

A commonly heard concern in the Ross procedure, where a diseased aortic valve is replaced by the patient's own pulmonary valve, is the possibility of pulmonary autograft dilatation. We performed a biomechanical investigation of the use of a personalized external aortic root support or exostent as a possibility for supporting the autograft. In ten sheep a short length of pulmonary artery was interposed in the descending aorta, serving as a simplified version of the Ross procedure. In seven of these cases, the autograft was supported by an external mesh or so-called exostent. Three sheep served as control, of which one was excluded from the mechanical testing. The sheep were sacrificed six months after the procedure. Samples of the relevant tissues were obtained for subsequent mechanical testing: normal aorta, normal pulmonary artery, aorta with exostent, pulmonary artery with exostent, and pulmonary artery in aortic position for six months. After mechanical testing, the material parameters of the Gasser-Ogden-Holzapfel model were determined for the different tissue types. Stress-strain curves of the different tissue types show significantly different mechanical behavior. At baseline, stress-strain curves of the pulmonary artery are lower than aortic stress-strain curves, but at the strain levels at which the collagen fibers are recruited, the pulmonary artery behaves stiffer than the aorta. After being in aortic position for six months, the pulmonary artery tends towards aorta-like behavior, indicating that growth and remodeling processes have taken place. When adding an exostent around the pulmonary autograft, the mechanical behavior of the composite artery (exostent + artery) differs from the artery alone, the non-linearity being more evident in the former

Developing a rent index for Flanders

This paper describes the development of a rent index for Flanders, Belgium. This annual index, referred to as the huurprijsindex (rent index), is designed to detect changes in the rent of the overall stock of rental homes. We use the matched model methodology based upon repeat tenancy agreements, analogous to Case and Shiller’s geometric repeat sales model, to estimate the rent index. We use recorded data on the tenancy agreements of nearly five hundred thousand rental homes; more than 30,000 representing repeat agreements between 1990 and 2010. The accuracy of the index is determined using the 95% confidence interval. Given our target (a geometric mean index value) and the characteristics of the dataset (large but without property characteristics) our repeat tenancy agreements method seems to be adequate for calculating a rent index for Flanders.OTB ResearchOTB Research Institute for the Built Environmen

Towards an index for the rental sector: A model for the Flanders housing market

OTB ResearchOTB Research Institute for the Built Environmen

Een huurprijsindex voor Vlaanderen

Vlaanderen heeft geen betrouwbare informatie over de ontwikkeling van huurprijzen. Huurcontracten in Vlaanderen hebben veelal een looptijd van een, drie of negen jaar. Bij het aangaan van een nieuwe huurovereenkomst kan de verhuurder vrij de huurprijs bepalen. Vanaf 2007 is gestart met het registeren van deze overeenkomsten en is een inventarisatie gemaakt van lopende overeenkomsten. Dit artikel beschrijft de ontwikkeling van een huurprijsindex voor Vlaanderen en geeft een beeld hiervan over het laatste decennia .OTB ReseachOTB Research Institute for the Built Environmen