Disparate effect of early wave reflection in aortic pressure and aortic flow velocity waveform

Objective: Previous studies have shown the reciprocal effects of wave reflection on aortic pressure and aortic flow waves. Invasive (Electro-Magnetic (EM)) and non-invasive (Cardiac Magnetic Resonance (CMR)) studies of aortic blood flow have shown characteristic aging changes as reduction in late systolic flow, which corresponds in time to the late systolic boost of aortic pressure. These are not always apparent in Doppler flow tracings.

Design and method: This study aimed to better understand the mechanisms of aortic pressure and flow changes due to early wave reflection and stiffening of arteries. Using SphygmoCor system, radial artery pressure waveforms were collected from 161 male subjects (age 21-80 years) undergoing cardiac catheterisation for suspected coronary disease. Ascending Aortic (AA) pressure was derived from radial artery pressure using validated transform function (SphygmoCor). AA flow velocity waves were generated from AA pressure and age-related AA impedance using mathematical relations governing flow and pressure in the frequency domain and solved using discrete Fourier transform analysis (Matlab v2014).

Results: Pressure (PAIx) and Flow Augmentation Index (FAIx), as manifestations of AA impedance and wave reflection, were compared (table). FAIx shows significant decrease with age, whereas PAIx increases with age, as shown in previous EM and CMR studies (figure). Findings are consistent with the disparate effect of early wave reflection with aging; aging augments aortic pressure in late systole while simultaneously lowering AA late systolic flow velocity. This inverse relationship, when combined, summates to a straight line which approximates zero (figure). No such relationship was seen with conventional aortic Doppler waveforms.

Conclusions: Findings confirm the reciprocal effect of early wave reflection which adds to AA pressure and subtracts from AA flow velocity. This gives fresh insight into Left Ventricular (LV) failure with preserved or reduced LV ejection fraction. ... "Might wave reflection be the cause of both?"