An approach to the simulation of fluid-structure interaction in the aortic valve.

A pair of finite element models has been employed to study the interaction of blood flow with the operation of the aortic valve. A three-dimensional model of the left ventricle with applied wall displacements has been used to generate data for the spatially and time-varying blood velocity profile across the aortic aperture. These data have been used as the inlet loading conditions in a three-dimensional model of the aortic valve and its surrounding structures. Both models involve fluid-structure interaction and simulate the cardiac cycle as a dynamic event. Confidence in the models was obtained by comparison with data obtained in a pulse duplicator. The results show a circulatory flow being generated in the ventricle which produces a substantially axial flow through the aortic aperture. The aortic valve behaves in an essentially symmetric way under the action of this flow, so that the pressure difference across the leaflets is approximately uniform. This work supports the use of spatially uniform but temporally variable pressure distributions across the leaflets in dry or structural models of aortic valves. The study is a major advance through its use of truly three-dimensional geometry, spatially non-uniform loading conditions for the valve leaflets and the successful modelling of progressive contact of the leaflets in a fluid environment.

High-level quinolone resistance in Neisseria gonorrhoeae: a report of two cases.

BACKGROUND AND OBJECTIVES: Fluoroquinolones are widely used oral agents for treating Neisseria gonorrhoeae. Resistance to these agents is sporadic and usually at a low level. Two instances of high-dose ciprofloxacin regimens failing in the treatment of gonococcal infection, caused by strains with high-level quinolone resistance, are reported. STUDY DESIGN: This is a case report. CONCLUSION: High-level resistance to quinolone antibiotics resulting in treatment failure was observed in two distinct gonococcal isolates from patients infected in the Philippines (ciprofloxacin; minimal inhibitory contribution = 16 mg/l). Continued monitoring of the quinolone sensitivity of Neisseria gonorrhoeae is appropriate and prudent.