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Influence of Serial Coronary Stenoses on Diagnostic Parameters: An In-vitro Study with Numerical Validation

D Souza, Gavin A

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2014, MS, University of Cincinnati, Engineering and Applied Science: Mechanical Engineering.

Coronary artery disease, a common cause of death in the US, is mainly caused by blockages in the coronary artery (coronary stenosis). Currently, diagnosis of coronary stenosis is primarily based on the well-established functional diagnostic parameter, fractional flow reserve (FFR: ratio of pressures distal and proximal to a stenosis). The threshold of FFR has a “gray” zone of 0.75-0.80, below which further clinical intervention is recommended. An alternate diagnostic parameter, pressure drop coefficient (CDP: ratio of trans-stenotic pressure drop to the proximal dynamic pressure), developed based on fundamental fluid dynamics principles, has been suggested by our group. Multiple stenoses may be present in series within a single vessel. An additional stenosis, present downstream, reduces the hyperemic flow (flow at maximum vessel vasodilation) and pressure drop across an upstream stenosis. Such hemodynamic variations may alter the values of FFR and CDP of the upstream stenosis. Therefore, there is a need to delineate the effect of the downstream stenosis from the upstream stenosis for accurate diagnosis of the upstream stenosis severity.

In vitro experiments simulating physiologic conditions, along with human data, were used to evaluate nine combinations of serial stenoses. Different cases of upstream stenosis (mild: 64% area stenosis [AS], intermediate: 80% AS, severe: 90% AS) were tested under a varying degree of downstream stenosis (mild, intermediate, and severe). In addition, a numerical analysis of the serial stenoses combinations with a fixed upstream intermediate stenosis was conducted using computational fluid dynamics (CFD).

In general, hyperemic flow and pressure drop across the upstream stenosis decreased when the downstream stenosis severity was increased. The FFR of the upstream mild, intermediate, and severe stenosis increased by a maximum of 3%, 13%, and 19%, respectively, when the downstream stenosis severity was increased from mild to severe. FFR of a standalone intermediate stenosis under clinical setting is reported to be ~ 0.72. In the presence of a downstream stenosis, FFR values of the upstream intermediate stenosis were either within (0.77 for 80%-64% AS and 0.79 for 80%-80% AS) or above (0.88 for 80%-90% AS) the “gray” zone, defined for FFR. This artificial increase in FFR value for an upstream intermediate stenosis when in series with a clinically relevant downstream stenosis could lead to misinterpretation of functional stenosis severity. In contrast, a distinct range of CDP values was observed for each case of upstream stenosis (mild: 8-10, intermediate: 47-54, and severe: 130-155). The non-overlapping range of CDP could better delineate the effect of the downstream stenosis and allow for accurate diagnosis of the functional severity of the upstream stenosis.

Comparable numerical FFR values were obtained for the 80%-64% AS, 80%-80% AS, and 80%-90% AS cases and were within 7% of the experimental FFR values for the corresponding cases. A maximum difference of 28% was observed between the numerical and experimental CDP values for the corresponding cases. A similar trend, observed between numerical and experimental values, indicates that the complex flow through serial stenoses may be accurately modeled computationally and this may provide alternate means for cardiovascular diagnosis.

Rupak Banerjee, Ph.D P.E. (Committee Chair)
Michael Taylor, M.D. Ph.D. (Committee Member)
Sundararaman Anand, Ph.D. (Committee Member)
77 p.

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Citations

  • D Souza, G. A. (2014). Influence of Serial Coronary Stenoses on Diagnostic Parameters: An In-vitro Study with Numerical Validation [Master's thesis, University of Cincinnati]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1397234083

    APA Style (7th edition)

  • D Souza, Gavin. Influence of Serial Coronary Stenoses on Diagnostic Parameters: An In-vitro Study with Numerical Validation. 2014. University of Cincinnati, Master's thesis. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=ucin1397234083.

    MLA Style (8th edition)

  • D Souza, Gavin. "Influence of Serial Coronary Stenoses on Diagnostic Parameters: An In-vitro Study with Numerical Validation." Master's thesis, University of Cincinnati, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1397234083

    Chicago Manual of Style (17th edition)