Mechanism underlying the heart rate dependency of wave reflection in the aorta: a numerical simulation

Arterial wave reflection has been shown to have a significant dependence on heart rate (HR). However, the underlying mechanisms inherent in the HR dependency of wave reflection have not been well established. This study aimed to investigate the potential mechanisms and role of arterial viscoelasticity using a 55-segment transmission line model of the human arterial tree combined with a fractional viscoelastic model. At varying degrees of viscoelasticity modeled as fractional order parameter α, reflection magnitude (RM), reflection index (RI), augmentation index (AIx), and a proposed novel normalized reflection coefficient (Γ_norm) were estimated at different HRs from 60 to 100 beats/min with a constant mean flow of 70 ml/s. RM, RI, AIx, and Γ_norm at the ascending aorta decreased linearly with increasing HR at all degrees of viscoelasticity. The means ± SD of the HR dependencies of RM, RI, AIx, and Γ_norm were -0.042 ± 0.004, -0.018 ± 0.001, -1.93 ± 0.55%, and -0.037 ± 0.002 per 10 beats/min, respectively. There was a significant and nonlinear reduction in RM, RI, and Γ_norm with increasing α at all HRs. In addition, HR and α have a more pronounced effect on wave reflection at the aorta than at peripheral arteries. The potential mechanism of the HR dependency of wave reflection was explained by the inverse dependency of the reflection coefficient on frequency, with the harmonics of the pulse waveform moving toward higher frequencies with increasing HR. This HR dependency can be modulated by arterial viscoelasticity. NEW & NOTEWORTHY This in silico study addressed the underlying mechanisms of how heart rate influences arterial wave reflection based on a transmission line model and elucidated the role of arterial viscoelasticity in the dependency of arterial wave reflection on heart rate. This study provides insights into wave reflection as a frequency-dependent phenomenon and demonstrates the validity of using reflection magnitude and reflection index as wave reflection indexes.