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SUMMARY:Modeling adaptive processes: vascular remodeling - Pries\, A (Frei
 e\, Berlin)
DTSTART:20090721T091500Z
DTEND:20090721T093000Z
UID:TALK19143@talks.cam.ac.uk
CONTACT:Mustapha Amrani
DESCRIPTION:Dynamic biological systems adapt to changes in internal or ext
 ernal conditions. A typical example is the response of the vascular system
  to changes in body size or local tissue function. Also during development
 \, adaptive responses are used widely to determine the design of body syst
 ems. Such reactions entail functional or structural feedback signals which
  are typical for the system considered. In the case of the vascular system
 \, the most relevant signals are generated by hemodynamics (local blood pr
 essure and wall shear stress) and the metabolic situation determined by th
 e relation between supply and demand (e.g. of oxygen). According to the us
 ual approach\, reactions to such signals are established in experimental c
 onditions aiming at a single stimulus at a time and interrupting the invol
 ved feedback loop. Such experiments showed an increase of vessel diameter 
 with increasing flow or metabolic demand and a decrease with increasing pr
 essure. Such reactions seem to be reasonable and the described reactions m
 ay be congruent with observed system responses under certain conditions (e
 .g. lower resistance for higher perfusion). Thus they are frequently used 
 as the basis for concepts of vascular adaptation or design. However\, the 
 isolated appreciation of individual reaction patterns can not support an u
 nderstanding of system properties in several aspects: The quantitative rel
 ation of the different reactions is not addressed\, it is not possible to 
 determine whether the observed reactions are necessary and sufficient to e
 xplain system behavior and the stability of the assumed feedback regulatio
 n can not be assessed. To answer such questions\, a mathematical descripti
 on or modeling of the assumed responses in a functional context is needed.
  Obviously\, the prerequisite for such modeling is a gross simplification 
 of the biological situation raising questions as to the validity of the ob
 tained results. However\, by not pertaining to specific biological propert
 ies lost in the simplification\, the modeling analysis should represent ge
 neral characteristics of systems which fit into the assumptions made in th
 e model. With respect to vascular adaptation\, mathematical models were\, 
 e.g.\, able to demonstrate that a directed information transfer along the 
 vessel wall is necessary to prevent maldistribution of the blood flow with
 in the tissue and the generation of functional shunting. Such a finding sh
 ould be independent of the biological implementation of the information tr
 ansfer but should stimulate respective experimental investigations. Based 
 on the respective findings intuitive assumptions on systems behavior can t
 hen be tested by more detailed and more realistic models. 
LOCATION:Seminar Room 1\, Newton Institute
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