Viscoelasticity modulates resonance in the terminal aortic circulation

Area of Science:

• Cardiovascular Physiology
• Biomedical Engineering
• Hemodynamics

Background:

• Aortic impedance patterns and oscillatory flow phenomena require sophisticated models for interpretation.
• The terminal aortic circulation exhibits complex pressure and flow dynamics influenced by arterial properties.

Purpose of the Study:

• To interpret aortic impedance patterns and explain oscillatory flow phenomena using an inertance-viscoelastic windkessel model.
• To investigate the role of viscoelasticity in terminal aortic impedance and resonance.

Main Methods:

• An inertance-viscoelastic windkessel model was developed, incorporating inertance (L), peripheral resistance (Rp), and a Voigt cell (resistor Rd, capacitor C).
• Pressure and flow measurements were obtained from the terminal aorta of anesthetized dogs under varying hemodynamic conditions.
• Model parameters (L, C, Rd) were estimated by fitting model-predicted flow waves to measured data.

Main Results:

• Prominent flow wave oscillations from midsystole to diastole were linked to resonance at a frequency (f(o)) where inertance and compliance reactances matched.
• Estimated resonance frequencies (f(o)) increased with mean arterial pressure (40-140 mm Hg), correlating with arterial elastic moduli.
• Viscous losses (Rd) in arterial wall motion were found to limit the amplitude of the resonance peak.

Conclusions:

• Viscoelasticity, rather than pure elasticity, is essential for interpreting terminal aortic impedance and associated resonance phenomena.
• The inertance-viscoelastic windkessel model effectively explains observed oscillatory flow patterns in the canine terminal aorta.
• Arterial wall viscoelasticity plays a significant role in modulating resonance characteristics within the aorta.