Impact of Dynamic Axial Stretching on the Arterial Pulse Wave Velocity: Physical Foundation and Clinical Implications

The conventional derivation of the pressure pulse wave velocity (PWV) relies on the wave equation for blood flow in a uniform elastic artery, wherein PWV is considered dependent on the linear elasticity of the artery and on the blood density. Arterial elasticity is represented by transverse compliance, i.e., assuming that the artery is fixed lengthwise. However, arteries exhibit a nonlinear and anisotropic stretch-stress behavior, challenging the conventional PWV equation based on a linear stretch-stress relationship. Moreover, the ascending thoracic aorta (ATA) undergoes dynamic axial elongation during the cardiac cycle, which co-determines its biomechanical response. This study establishes a derivation for understanding how this dynamic axial elongation affects local PWV in a hyperelastic ATA.

ATA compliance was analytically derived by relating the diameter change to changes in the intraluminal pressure and axial stretch. Synthetic pressure-diameter curves were generated using the Gasser-Ogden-Holzapfel model, assuming a thin-walled cylinder with an axial stretch of 1.2 at diastolic pressure and axial strains of 0, 2, 4, 6, and 8% superimposed to the diastolic-to-systolic pressurization. Compliance values were calculated using two methods: 1) the slope of diameter-pressure curves and 2) our analytical derivation. For comparison, PWV was determined by using the obtained compliance values in the conventional wave equation.

Our derived compliance agreed with the compliance calculated from the slope of the diameter-pressure curves. PWV increased with axial strains, even at a constant pressure.

In clinical studies, it is important to consider the influence of dynamic axial elongation on PWV measurements.