Ein Beitrag zur Modellbildung und Simulation Ballondilatation von Atemwegstenosen (English shop)

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This dissertation examines the mechanical processes occurring during balloon dilatation of airway stenoses.

The stenoses considered here, of the “cicatricial stricture” type, are usually dilated manually in routine clinical practice using a dilatation balloon. If necessary, stent implantation follows. The selection of the stent, including its characteristic curve, is made intuitively or according to personal experience and preferences. In order to achieve an optimal treatment result, however, adaptation to the stress-strain behaviour of the stenosis is necessary. This behaviour is not determined during manually performed balloon dilatation.

The aim is to determine, experimentally and theoretically on the basis of models, the relationships between the pressure-volume curve measured during dilatation and the stress-strain behaviour of the stenosis. In doing so, account is taken of the particular circumstance that, when a cicatricial stricture is dilated, the dilatation balloon is only partially constricted by the stenosis; it protrudes beyond the stenosed region at both ends.

Experimental investigations are carried out on model stenoses of differing extensibility and length. As expected, harder stenoses lead to a steeper rise in the curve during the dilatation phase. In contrast, a comparison between stenoses of equal extensibility but different length shows an initially unexpected greater strain of the shorter stenosis for the same increase in pressure. The reason for this is that the marginal regions of the stenoses experience a temporal head start in strain compared with the regions situated further inside. For this behaviour, which is more pronounced in shorter stenoses, the term “edge strain effect” is introduced.

The modelling of the dilatation process is based, on the one hand, on equilibrium considerations of the free-body balloon and, on the other hand (by way of comparison), on the principle of the minimum of total potential energy. The balloon/stenosis system is divided into three sub-regions for which different conditions apply. The regions considered are: 1. the proximal and distal balloon regions outside the stenosis; 2. the region in which balloon and stenosis come into contact; 3. the transition region between 1 and 2.

Numerical simulations of balloon dilatation confirm the findings obtained from the experimental investigations and theoretical considerations regarding the relationships between the pressure-volume curve of the dilatation and the stress-strain behaviour of the stenosis.