Table 1 Overview of PDF parameters
Parameter | Name | Unit (SI unit) | Physiological description |
|---|---|---|---|
x 0 | Load | cm | Related to the load that is compressing the elastic myocardium at end systole, a prerequisite for a restoring force to arise. Closely related to the velocity time integral (VTI) of the E-wave. |
k | Stiffness | g/s2 (N/m) | LV rigidity, or the extent to which the LV resists deformation in response to an applied force. Linearly related to chamber stiffness [3] (dP/dV), and thus influences the restoring force that drives early diastolic filling. Increased in hypertension [8]. |
c | Viscoelasticity | g/s (N∙s/m) | Energy loss or damping of LV recoil, caused by impaired relaxation and increased viscoelasticity of the myocardium. Increased in diabetes [6] and hypertension [8]. |
Vmax | E-wave peak velocity | m/s | Peak velocity of blood flow across the mitral valve during early LV filling. |
kx 0 | Peak driving force | mN | The peak force driving LV filling, analogous to the peak atrioventricular pressure gradient [14]. The product of k and x 0 , |
cVmax | Peak resistive force | mN | The force resisting filling at peak transmitral flow. The product of c and Vmax. |
1/2kxo2 | Filling energy | mJ | Stored potential elastic energy from systole that generates rapid early LV filling. Increased in hypertension [8]. |
c2 − 4k or β | Damping index | g2/s2 (kg∙N/m) | Reflects the balance between the factors driving and resisting left ventricular filling. Values < −900 g2/s2 are a strong predictor of 1-year mortality in elderly with heart failure [9]. |
KFEI | Kinematic filling efficiency index | % | An index that characterizes the efficiency of LV filling. Calculated as the ratio of the velocity time integral of the actual E-wave to the velocity time integral of a PDF model-predicted ideal E-wave contour with no resistance to filling (c = 0) but the same stiffness (k) and load (x0) as for the original E-wave. Reduced in diabetes [7]. |
tau | Time constant of isovolumic pressure decay | ms | Tau is used to characterize LV filling based on time-resolved high fidelity invasive measurements of LV pressure. Increased in impaired relaxation. Can be approximated by combination of PDF parameters [4]. |
M | Load independent index of diastolic filling | unitless | A load independent index of diastolic filling, which is decreased in patients with diastolic dysfunction and increased LV end-diastolic pressure [5]. Describes the ratio of change in peak driving force to change in peak resistive force (Δkx0/ΔcVmax), calculated after acquiring E-waves under varying loading conditions. |
B | Intercept | mN | An index of diastolic filling that is increased in patients with diastolic dysfunction and increased LV end-diastolic pressure [5]. Mathematically, the y-axis intercept of the relationship between the peak driving and resistive forces from E-waves acquired under varying loading conditions. |