Acne Scars

Biomed Tech (Berl). 2009 Jul 14; Venhaus M, Behn C, Freitag L, Zimmermann KAbstract This article investigates the mechanics of balloon dilatation in the treatment of bronchotracheal stenosis. The "scar stricture"-type stenosis examined in this paper is typically dilated manually, using a dilatation balloon. If indicated, this is followed by stent implantation. The selection of the stent with proper characteristics is performed empirically, based on personal experience and preference. In order to optimize the therapeutic outcome, however, it is necessary to match the stent with the stress-strain properties of the stenosis, which are not determined during manual balloon dilatation. The objective is to utilize models to experimentally and theoretically establish the correlation between the pressure/volume curve measured during the dilatation and the stress-strain properties of the stenosis, taking into account that during dilatation of scar strictures the balloon is only partially compressed, as it extends beyond both ends of the stenosis. Experiments are carried out using stenosis models with various extensibilities and lengths. As expected, more hardened stenosis resulted in steeper pressure/volume curves during the dilatation. On the other hand, the comparison between stenosis of equal extensibilities, but different length, showed an initially unexpected larger distension of the shorter stenosis, at equal pressure increases. This is caused by the fact that the margins of the stenosis are allowed more time to distend, compared to the central areas of the stenosis. The term "effect of margin expansion" was introduced to describe this behavior. The modeling of the dilatation process is based on the equilibrium conditions of cut-free balloon portions. The balloon/stenosis system is divided into three areas with different characteristics: (1) the proximal and distal area of the balloon outside the stenosis; (2) the area of contact between the balloon and the stenosis; and (3) the transition area between (1) and (2). Numerical simulations of the balloon dilatation confirm the conclusions from the experimental results and the theoretical considerations regarding the correlation between the pressure/volume curve of the dilatation and the stress-strain properties of the stenosis.