| Summary: | Objectives: While in young subjects, central pressure and flow peaks occur simultaneously and before time to return of reflected pressure (Tr), Tr progressively shifts towards early systole with aging, and eventually occurs before pressure peak. Consequently such parameters along with the corresponding augmentation index (AIx) have been previously shown as relevant indices of arterial aging. However, Tr accurate determination using pressure alone remains challenging, especially in elderly subjects. Accordingly, our aim was to combine central pressure and flow waveforms to provide objective and reproducible reflections-related indices.
Methods: We studied 50 healthy subjects (24 women, age: 46±15years), who underwent ascending aorta velocity-encoded magnetic resonance (1.5T) and carotid applanation tonometry. For each subject, time delays between Tr and peak flow (TQmax-Tr) and between pressure and flow peaks (TQ-Pmax), which are related to the overlap between incident and reflected pressure waves, were automatically estimated using a custom software that enables superimposition of pressure and flow waveforms. Conventional AIx was also measured from carotid pressure waveform. Forward and backward pressure components obtained using aortic characteristic impedance were used to estimate reflection magnitude (RM) as the ratio between backward and forward pressure magnitudes.
Results: The obtained correlations for comparison against age, AIx and RM were higher for TQ-Pmax than for Tr or TQmax-Tr (Table). Importantly association with RM, which is known to be a pure index of wave reflection, was superior for the combined index TQ-Pmax.
Conclusions: Superimposition of pressure and flow waveforms helps for an objective and reproducible evaluation of central reflections-related indices.
r (p)
Tr
TQmax-Tr
TQ-Pmax
Age
−0.51 (p=0.0002)
−0.42 (p=0.003)
0.69 (p<0.0001)
AIx
−0.77 (p<0.0001)
−0.60 (p<0.0001)
0.82 (p<0.0001)
RM
−0.46 (p=0.001)
−0.52 (p=0.0001)
0.84 (p<0.0001)
Table.Comparison of reflection indices against age, augmentation index (AIx) and reflection magnitude (RM).
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