# Calculation of Intracoronary Pressure-Based Indexes with JLabChart
## 2 Material and Methods
### Fractional Flow Reserve  
We refer to the FFR index to measure intracoronary pressure and to evaluate stenosis severity [40]. The maximal vasodilation of the microcirculation, known as maximal hyperemia, is induced by adenosine and papaverine. The FFR index is evaluated by considering the proximal aortic pressure \(P_{a}\) and the distal coronary artery pressure \(P_{d}\). Figure 4 reports a schematic representation of the FFR at the maximum vasodilation condition, where a condition without lesions is shown at the top and a condition with stenosis at the bottom.  
Figure 3: Dicrotic notch point and wave-free period characteristics in the blood pressure signal.  
In the latter case, the stenosis is responsible for a hyperemic pressure gradient \(\Delta\)P of 30 mmHg; so, the driving pressure ranges from 100 mmHg to 70 mmHg (\(P_{d}\)). During maximal hyperemia, the relationship between the driving pressure and myocardial blood flow is linear and the myocardial blood flow reaches 70% of its normal value. \(P_{a}\), \(P_{d}\), and \(P_{p}\) indicate (i) aortic pressure values in the proximity of the vessel lesion, (ii) the coronary artery pressure distal to the lesion and the (iii) central venous pressure, respectively. Finally, \(R_{min}\) is the minimal myocardial resistance. The FFR is defined as in Equation (2):  
\[FFR=\frac{Q_{stenosis}^{max}}{Q_{normal}^{max}} \tag{2}\]  
where \(Q_{stenosis}^{max}\) is the maximum myocardial blood flow in the presence of stenosis, and \(Q_{normal}^{max}\) represents the maximum myocardial flow in a normal condition. \(Q_{normal}^{max}\) and \(Q_{stenosis}^{max}\) are evaluated as the ratio between the pressure value and the coronary index of resistance, as expressed in Equations (3) and (4). In particular:  
\[Q_{normal}^{max}=\frac{(P_{a}-P_{v})}{R_{min}} \tag{3}\]  
\[Q_{stenosis}^{max}=\frac{(P_{d}-P_{v})}{R_{min}}. \tag{4}\]  
By using these values in Equation (2), the FFR can be expressed in the following Equation (5):  
\[FFR=\frac{Q_{stenosis}^{max}}{Q_{normal}^{max}}=\frac{(P_{p}-P_{v})}{\frac{(P _{v}-P_{v})}{R}}. \tag{5}\]  
By considering the central venous pressure (\(P_{v}\)) as negligible, the FFR formula may be also simplified as in Equation (6):  
\[FFR=\frac{P_{d}}{P_{a}}. \tag{6}\]  
The FFR is a dimensionless parameter, which can be expressed with values between 0 and 1 indicating an occluded vessel or a healthy vessel, respectively. In a healthy coronary artery, the FFR is equal to 1 because the pressure in the origin and in the distal tract of a healthy vessel is the same, even during maximal hyperemia. In the presence of stenosis, however, the blood pressure downstream is lower than the measured one from the guide catheter tip, during maximal hyperemia, so the FFR is reduced. In particular, \(FFR>0.80\)  
Figure 4: Graphical representation of Fractional Flow Reserve (FFR). (**a**) FFR represented graphically in the vessels; (**b**) FFR as the ratio between maximum blood flow distal to a stenotic lesion to normal maximum flow in the same vessel.  
means that the stenosis presents a minimal hemodynamic impairment and is not associated with clinical risk.