Table 1.

A list of parameters used to measure arterial stiffness.

Definition (unit)	Formula	Notes
Pressure-strain modulus, Eρ (Pa)		R can also be replaced with diameter (D). Extrinsic mechanical property
Elastic modulus, E (Pa)		The slope of stress-strain (σ −  ε) curve, assuming linear homogenous, incompressible wall material. Thin-wall or thick-wall assumptions lead to different calculations of σ and ε. Intrinsic material property
Incremental elastic modulus (1), E inc (Pa)		R o and R i are external and internal radii and can be replaced with corresponding diameters (D). Assuming locally linear, homogenous, incompressible (if ν = 0.5) wall material. Thick wall assumption. Intrinsic material property
Incremental elastic modulus (2), E inc (Pa)		Modified E inc assuming orthotropic cylindrical tube. Intrinsic material property
Stiffness constant, β (dimensionless)		P s and P d are systolic and diastolic pressures. Radius R can be replaced with diameter (D). Assume homogenous, incompressible, isotropic material. Extrinsic mechanical property
Distensibility, D, (1/Pa)		V (volume) can be replaced with A (area). Extrinsic mechanical property
Compliance, C, (m 3/Pa)		V (volume) can be replaced with A (area). Extrinsic mechanical property

P =  pressure, R =  radius, D =  diameter, V =  volume, A =  area. Adapted from Wang Z, Chesler NC. Pulmonary vascular wall stiffness: An important contributor to the increased right ventricular afterload with pulmonary hypertension. Pulm Circ. 2011;1(2):212–223.