Ascending Aortic Impedance In Young Endurance Athletes: A Time-resolved Phase-contrast MRI Study

Ventricular-vascular coupling in endurance athletes remains incompletely understood. PURPOSE: To determine the ascending aortic impedance in endurance athletes and explore its associations with traditional cardiovascular measurements. METHODS: In 15 young endurance runners and 19 age- and sex-matched sedentary participants, time-resolved (CINE) 2D phase-contrast MRI quantified the ascending aortic flow while the pressure waveform was simultaneously collected via a generalized transfer function. The aortic impedance modulus and phase were calculated in the frequency domain while characteristic impedance (Zc) was calculated by averaging moduli between the 4th and 8th heart rate (HR) harmonics. Stroke volume (SV) left ventricular (LV) morphometry, double product, aortic compliance, and total peripheral resistance (TPR) were also measured. RESULTS: Endurance athletes had higher SV (97 ± 18 vs. 82 ± 11 mL, p = 0.007), slower HR (49 ± 5 vs. 58 ± 9, p = 0.001), greater LV volume and mass, and lower double product than sedentary participants (all p < 0.05). The modulus showed significant group, harmonic, and interaction effects (p < 0.001), with the athlete group exhibiting significantly lower modulus at the 7th (p = 0.011) and 8th (p < 0.001) harmonics than the sedentary group. A significant harmonic effect was observed for the phase angle. Zc was significantly lower in athletes than in sedentary participants (73.3 ± 19.2 vs. 93.4 ± 19.0 dyn-sec/cm5, p = 0.005). Furthermore, Zc was negatively correlated with SV (r = -0.691) and aortic compliance (r = -0.601) but was positively correlated with double product (r = 0.445) and TPR (r = 0.458) (all p < 0.05). Multivariate analysis revealed that Zc was the strongest predictor of SV followed by TPR, HR, and double product (overall model R2 = 0.852, p < 0.001). CONCLUSIONS: Our findings collectively suggest that LV afterload quantified by Zc is significantly lower in endurance athletes than in sedentary adults. This lower LV afterload may contribute to an efficient generation of SV in endurance athletes. Japan Society for the Promotion of Science (22H03491, 461 TT)