A novel system for the investigation of microvascular dysfunction including vascular permeability and flow-mediated dilatation in pressurised human arteries.

INTRODUCTION: Adverse drug reactions may be manifested through changes in microvascular function (e.g. angioedema) or by subtle modification of the mechanisms controlling vascular tone, such as flow-mediated dilatation. Until now the early detection of such adverse drug reactions has been hampered by the lack of a predictive in vitro model. This in vitro model can be utilised to test potential effect of drugs on the normal responses of the vascular system. METHODS: The PM-1, a new automated perfusion myograph, allows detection of the external and internal dimensions of tubular biological structures and regulates both the intraluminal pressure and flow independently. Drugs can be infused intraluminally or extraluminally (by adding to the bathing solution) to determine effects on constriction, relaxation or modulation of vascular tone. The novel imaging system also facilitates the measurement of vascular permeability using dyes introduced intraluminally into the vessel. RESULTS: To assess effects on flow-mediated dilatation we increased flow rate in pressurised human subcutaneous arteries (<500mum diameter) in the absence and presence of various drugs. Increasing flow from 0.04ml/min to 0.3ml/min resulted in a 39+/-3% relaxation of a U46619 pre-constriction (10(-6)M). This was enhanced in the presence of Ivermectin and inhibited in the presence of 100microM L-NAME (316+/-169% and 16+/-1% respectively).To assess effects on vascular permeability we infused albumin-bound Evans blue dye through the lumen of human subcutaneous arteries as a marker, in the absence and presence of a modulatory drug. Infusion of thrombin (0.5units/ml) through the vessel lumen caused an 11.8% increase in vessel permeability compared to vehicle infusion. CONCLUSION: The development of the PM-1 allows new drugs to be tested in relevant human or animal tissues at an early stage allowing crucial go/no-go decisions to be made early in development and giving a more complete picture of the overall effects of test compounds on vascular function.

Computational fluid dynamics insights in the design of mechanical heart valves.

Computational fluid dynamics (CFD) analysis can provide detailed, three-dimensional predictions of blood flow through mechanical heart valves, which can help to optimize valve hemodynamics and reduce the potential for blood clotting. A number of CFD studies, considering both forward and retrograde flow through valves, have been published. In this paper, a geometrically accurate CFD model capable of predicting the three-dimensional, time-dependent flow through an open ATS bileaflet valve is presented. A detailed picture of the blood flow is obtained, including small-scale flow features in the pivot regions. Results from the model can also be used to investigate the opening position of the ATS valve leaflets. Future work will be aimed toward improved models that provide valuable design information while minimizing the development time and computational resources required. Such practical CFD models clearly have the potential to reduce the costs, time scales, and risks associated with development of new heart valve designs.