Noninvasive hemodynamic indices of vascular aging: an in silico assessment

Figures

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  Figure 1.. A: simulated pressure and flow velocity waveforms at the measurement arterial sites used in this study. B: schematic of the one-dimensional blood flow model that produced the in silico data. C: photoplethysmogram (PPG) waveforms at several body sites. Each waveform is shown for the baseline subject in each age decade from 25 to 75 yr (see Ref. 10 for details).

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  Figure 2.. A: Young’s modulus (E) as a function of luminal arterial radius (r) for the baseline subject in each age decade. B: variation of the averaged E along the aorta (calculated using Eq. 2) with age for all virtual subjects. Solid line, mean values; dashed lines, ±1SD.

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  Figure 3.. Pressure (A) and photoplethysmogram (PPG; B) fiducial points. P1, first inflection point/systolic peak; P2, 2nd inflection point/systolic peak, depending on the pressure wave type (45); Pf, peak pressure of the forward-traveling pressure wave; Pb, peak pressure of the backward-traveling pressure wave; s, PPG systolic peak amplitude; dia, PPG diastolic peak amplitude; PT1, PPG early systolic amplitude; PT2, PPG late-systolic amplitude; ΔT, time difference between systolic and diastolic PPG peaks; a, peak of early systolic positive wave of the second-derivative PPG; b, valley of early systolic negative wave of the second-derivative PPG; c, peak of late systolic reincreasing wave of the second-derivative PPG; d, valley of late systolic redecreasing wave of the second-derivative PPG; e, peak of early diastolic positive wave of the second-derivative PPG.

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  Figure 4.. Effect of different levels of signal-to-noise ratios (SNRs) on the aortic root pressure waveform (P; A), aortic root flow velocity waveform (U; B), and digital photoplethysmogram waveform (PPG; C). Red lines, waveforms with noise; black lines, filtered waveforms.

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  Figure 5.. Comparison of chronological age variation in vascular aging indices calculated from simulated waveforms (in silico) and waveforms collected from real subjects (in vivo). Indices are described in Table 1. Solid lines, mean values; dashed lines, ±1SD. In vivo data were obtained from Refs. 27, 29–31, 33, 34, 38–41, 44, 49–52, as specified in the plots.

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  Figure 6.. Relationship between each vascular aging index and aortic Young’s modulus (EAo) for all virtual subjects (black), 25-yr-old subjects (blue), and 75-yr-old subjects (red). See Table 1 for a description of each index. Spearman’s correlation coefficients (rs) and Pearson’s correlation coefficients (rp) are provided for all subjects in each plot. See Table 2 for the rs and rp values for young and elderly subjects.

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  Figure 7.. Physiological determinants of all indices assessed using the relative sensitivity index (I) calculated for three cardiac properties and three vascular properties.

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  Figure 8.. Bland–Altman plots comparing the six pulse wave velocity indices with the theoretical aortic pulse wave velocity (aoPWVt) calculated using Eq. 3. Each circle represents data from a virtual subject, and color code indicates age of each subject. Solid lines, mean difference values; dashed lines, ±1.96 SD.

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  Figure 9.. Variation in the absolute value of Spearman’s (rs) and Pearson’s (rp) correlation coefficients between each vascular aging index and aortic Young’s modulus (EAo) for different signal-to-noise ratios (SNRs).