Optimality and cost analysis in regressing vascular networks

Research project P 13799 Optimality and cost analyses in regressing vascular networks Alois LAMETSCHWANDTNER 28.06.1999 The cardiovascular system is a transport system which is of the closed type in man and of the open or closed type in animals. It transports oxygen and nutrients close to body cells and removes carbon dioxide and waste products therefrom. It further carries hormones and antibodies discharged into the blood stream all over the body to target sites, guides leucocytes to sites of antigen or foreign body intrusion, and participates in the regulation of body heat. In tumors it also serves tumor cells to escape the primary tumor to form life-threatening metastases (=secondary tumors) in e.g. brain, lung, liver, bone or other organs. Failures of the system lead to harzardous health risks and have become the second frequent cause for death in industrialized countries. Our project will test which of the four given optimization models (minimum pumping power, minimum resistance, minimum volume, minimum drag) matches an involving (=regressing) network of blood vessels best and to what extent the cost functions of vessel branchings change thereby. The vascular beds of ventral tail fin (having a simple 3D vascular network) and gills (having a complex 3D vascular network) of tadpoles of the South African Clawed Toad, Xenopus laevis Daudin which both regress totally while the tadpole undergoes metamorphosis serve as model vascular systems. The aims of the project are: -Analysis of in-vivo vascular patterns and blood circulation using intravital microscopy combined with videotaping and digital framegrabbing, -Analysis of structural changes of blood vessels using light microscopy and transmission electron microscopy, -Measurements of diameters of parent and daughter vessels, intervascular and interbranching distances, branching orders and branching angles in-vivo (intravital microscopy) and ex-vivo (3D morphometry of stereopaired scanning electron microscopy (SEM) images of vascular corrosion casts) -Computation of branching indices, area ratios (parent vessel : daughter vessels), cost functions) of branching angles, deviation(s) from optimum branchings, -Implementation of a software package enabling the computation of mean blood flow, blood pressure and blood velocity within the cast vascular networks using the data (diameters, interbranching distances. branching angles) gained by 3D morphometry and the intraluminal measurements of in-vivo blood pressure in the initial portion of segmental arterioles and/or segmental venules of the ventral tail fin by a micropressure system. Any knowledge of the physiological regression of blood vessels will help in establishing vessel targeted approaches to artifically (therapeutically) regress a disasterous blood vascular system, e.g. that of a life-threatening tumor.