In vitro Quantification of Guidewire Flow-Obstruction Effect in MODEL CORONARY STENOSES FOR INTERVENTIONAL DIAGNOSTIC PROCEDURE

The objective is to quantify the guidewire ( and preangioplasty). The diagnostic parameters measured before guidewire insertion (CFR and FFR) and during guidewire insertion (gCFR and gFFR) were validated numerically and correlated with the new diagnostic parameter "lesion flow coefficient (LFC)." There was significant flow reduction with increased trans-stenotic pressure drop due to guidewire insertion. The FFR-gFFR and CFR-gCFR correlations wer

Hemodynamic wall shear stress profiles influence the magnitude and pattern of stenosis in a pig AV fistula

Venous stenosis is a significant problem in arteriovenous fistulae, likely due to anatomical configuration and wall shear stress profiles. To identify linkages between wall shear stress and the magnitude and pattern of vascular stenosis, we produced curved and straight fistulae in a pig model. A complete wall stress profile was calculated for the curved configuration and correlated with luminal stenosis. Computer modeling techniques were then used to derive a wall shear stress profile for the straight arteriovenous fistula. Differences in the wall shear stress profile of the curved and straight fistula were then related to histological findings. There was a marked inverse correlation between the magnitude of wall shear stress within different regions of the curved arteriovenous fistula and luminal stenosis in these same regions. There were also significantly greater differences in wall shear stress between the outer and inner walls of the straight as compared to curved arteriovenous fistula, which translated into a more eccentric histological pattern of intima-media thickening. Our results suggest a clear linkage between anatomical configuration, wall shear stress profiles, and the pattern of luminal stenosis and intima-media thickening in a pig model of arteriovenous fistula stenosis. These results suggest that fistula failure could be reduced by using computer modeling prior to surgical placement to alter the anatomical and, consequently, the wall shear stress profiles in an arteriovenous fistula

Hemodynamic diagnostics of epicardial coronary stenoses: <it>in-vitro </it>experimental and computational study

<p>Abstract</p> <p>Background</p> <p>The severity of epicardial coronary stenosis can be assessed by invasive measurements of trans-stenotic pressure drop and flow. A pressure or flow sensor-tipped guidewire inserted across the coronary stenosis causes an overestimation in true trans-stenotic pressure drop and reduction in coronary flow. This may mask the true severity of coronary stenosis. In order to unmask the true severity of epicardial stenosis, we evaluate a diagnostic parameter, which is obtained from fundamental fluid dynamics principles. This experimental and numerical study focuses on the characterization of the diagnostic parameter, pressure drop coefficient, and also evaluates the pressure recovery downstream of stenoses.</p> <p>Methods</p> <p>Three models of coronary stenosis namely, moderate, intermediate and severe stenosis, were manufactured and tested in the <it>in-vitro </it>set-up simulating the epicardial coronary network. The trans-stenotic pressure drop and flow distal to stenosis models were measured by non-invasive method, using external pressure and flow sensors, and by invasive method, following guidewire insertion across the stenosis. The viscous and momentum-change components of the pressure drop for various flow rates were evaluated from quadratic relation between pressure drop and flow. Finally, the pressure drop coefficient (CDP_e) was calculated as the ratio of pressure drop and distal dynamic pressure. The pressure recovery factor (<it>η</it>) was calculated as the ratio of pressure recovery coefficient and the area blockage.</p> <p>Results</p> <p>The mean pressure drop-flow characteristics before and during guidewire insertion indicated that increasing stenosis causes a shift in dominance from viscous pressure to momentum forces. However, for intermediate (~80%) area stenosis, which is between moderate (~65%) and severe (~90%) area stenoses, both losses were similar in magnitude. Therefore, guidewire insertion plays a critical role in evaluating the hemodynamic severity of coronary stenosis. More importantly, mean CDP_eincreased (17 ± 3.3 to 287 ± 52, n = 3, <it>p </it>< 0.01) and mean <it>η </it>decreased (0.54 ± 0.04 to 0.37 ± 0.05, <it>p </it>< 0.01) from moderate to severe stenosis during guidewire insertion.</p> <p>Conclusion</p> <p>The wide range of CDP_eis not affected that much by the presence of guidewire. CDP_ecan be used in clinical practice to evaluate the true severity of coronary stenosis due to its significant difference between values measured at moderate and severe stenoses.</p