M.Sc Thesis

M.Sc StudentMouler Marie
SubjectMeasurement of Vascular Impedance in Coronary Circulation:
A New Approach to Assess Severity of Coronary
Artery Stenosis
DepartmentDepartment of Biomedical Engineering
Supervisors PROFESSOR EMERITUS Rafael Beyar
PROFESSOR EMERITUS Uri Dinnar (Deceased)


The severity of coronary stenoses is typically assessed by angiographic or intravascular ultrasound (IVUS) geometry based measurements. Additional physiological information may be obtained by determination of the fractional flow reserve (FFR) derived from trans-lesion pressure measurements, or the coronary flow velocity reserve (CFVR), calculated from Doppler velocity measurements during a hyperemic stimulus. Simultaneous measurements of pressures and blood flow velocity can provide additional data on the functional behavior of coronary stenosis. The main goal of the research was to develop new methods for characterization of coronary stenosis based on dynamic pressure and blood flow velocity measurements and to assess the value of frequency domain analysis in evaluating stenosis characteristics. Intracoronary pressures distal and proximal to the stenoses with simultaneous, Doppler wire blood flow velocity recordings were obtained at rest and during adenosine induced hyperemia.  Input impedance (Zin) was calculated from proximal coronary pressure and velocity curves. Stenosis impedance (Zs) was calculated from trans-stenosis gradients and velocity signals. Results were compared to the fractional flow reserve (FFR) measurements for basal and post coronary interventions states.

Input impedance, represented by input resistance (Rin,) and characteristic impedance (Zo) (defined as the average of first 8 harmonics). Stenosis impedance  (Zs), represented by integral over the first 4 basic harmonics. While both, Zin and ZS show a significant correlation with FFR, Zs is more sensitive to the changes induced by PCI (60 % decrease vs 45% decrease in Zin). Correlation between Zs and FFR is strongest in maximal hyperemia state. While Zin can not differentiate intermediate and mild stenosis, Zs demonstrated a difference between moderate and mild stenosis groups only during hyperemia. Zs may be an important parameter in characterization of stenosis severity, which accounts for both pressure gradients and flow.