Bernhard, S. (2006) Transient integral boundary layer method to calculate the translesional pressure drop and the fractional flow reserve in myocardial bridges. BioMedical Engineering OnLine, 5 (42).

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Official URL: http://dx.doi.org/10.1186/1475925X542
Abstract
Background The pressure drop – flow relations in myocardial bridges and the assessment of vascular heart disease via fractional flow reserve (FFR) have motivated many researchers the last decades. The aim of this study is to simulate several clinical conditions present in myocardial bridges to determine the flow reserve and consequently the clinical relevance of the disease. From a fluid mechanical point of view the pathophysiological situation in myocardial bridges involves fluid flow in a time dependent flow geometry, caused by contracting cardiac muscles overlying an intramural segment of the coronary artery. These flows mostly involve flow separation and secondary motions, which are difficult to calculate and analyse. Methods Because a three dimensional simulation of the haemodynamic conditions in myocardial bridges in a network of coronary arteries is timeconsuming, we present a boundary layer model for the calculation of the pressure drop and flow separation. The approach is based on the assumption that the flow can be sufficiently well described by the interaction of an inviscid core and a viscous boundary layer. Under the assumption that the idealised flow through a constriction is given by nearequilibrium velocity profiles of the FalknerSkanCooke (FSC) family, the evolution of the boundary layer is obtained by the simultaneous solution of the FalknerSkan equation and the transient vonKármán integral momentum equation. Results The model was used to investigate the relative importance of several physical parameters present in myocardial bridges. Results have been obtained for steady and unsteady flow through vessels with 0 – 85% diameter stenosis. We compare two clinical relevant cases of a myocardial bridge in the middle segment of the left anterior descending coronary artery (LAD). The pressure derived FFR of fixed and dynamic lesions has shown that the flow is less affected in the dynamic case, because the distal pressure partially recovers during reopening of the vessel in diastole. We have further calculated the wall shear stress (WSS) distributions in addition to the location and length of the flow reversal zones in dependence on the severity of the disease. Conclusion The described boundary layer method can be used to simulate frictional forces and wall shear stresses in the entrance region of vessels. Earlier models are supplemented by the viscous effects in a quasi threedimensional vessel geometry with a prescribed wall motion. The results indicate that the translesional pressure drop and the mean FFR compares favourably to clinical findings in the literature. We have further shown that the mean FFR under the assumption of HagenPoiseuille flow is overestimated in developing flow conditions.
Item Type:  Article 

Subjects:  Mathematical and Computer Sciences > Mathematics > Mathematical Modelling Subjects allied to Medicine > Anatomy > Pathology Mathematical and Computer Sciences > Mathematics > Applied Mathematics Mathematical and Computer Sciences > Mathematics > Engineering/Industrial Mathematics Subjects allied to Medicine > Medical Technology > Biomechanics Mathematical and Computer Sciences > Mathematics > Numerical Analysis 
ID Code:  948 
Deposited By:  Dr. Stefan Bernhard 
Deposited On:  22 Sep 2010 09:24 
Last Modified:  03 Mar 2017 14:40 
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