Research

Hemodynamic diagnostics of epicardial coronary stenoses: in-vitro experimental and computational study

Rupak K Banerjee^1,4 , Koustubh D Ashtekar¹ , Tarek A Helmy² , Mohamed A Effat² , Lloyd H Back^{* 3} and Saeb F Khoury²

¹Department of Mechanical, Industrial and Nuclear Engineering, 601B Rhodes Hall, University of Cincinnati, Clifton Avenue, Cincinnati, OH, USA

²Department of Internal Med-Cardiology, MSB, University of Cincinnati, Cincinnati, OH, USA

³Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA

⁴Department of Biomedical Engineering, 598 Rhodes Hall, PO Box 210072, Cincinnati OH, 45221 0072, USA

author email corresponding author email* Contributed equally

BioMedical Engineering OnLine 2008, 7:24doi:10.1186/1475-925X-7-24

Published:	27 August 2008

Abstract

Background

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.

Methods

Three models of coronary stenosis namely, moderate, intermediate and severe stenosis, were manufactured and tested in the in-vitro 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 (η) was calculated as the ratio of pressure recovery coefficient and the area blockage.

Results

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_e increased (17 ± 3.3 to 287 ± 52, n = 3, p < 0.01) and mean η decreased (0.54 ± 0.04 to 0.37 ± 0.05, p < 0.01) from moderate to severe stenosis during guidewire insertion.

Conclusion

The wide range of CDP_e is not affected that much by the presence of guidewire. CDP_e can 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.