Comparison of arterial wave intensity analysis by pressure–velocity and diameter–velocity methods in a virtual population of adult subjects

Figures

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  Figure 1.. Depiction of the 55 artery network. 17

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  Figure 2.. Ten example inflow waveforms with periods scaled to match to allow easier comparison. Peak volume fluxes were between 400 mL/s and 600 mL/s, and stroke volumes were between around 60–110 mL, which is within the physiological range for healthy adults. 27

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  Figure 3.. From top to bottom, pressure, diameter, velocity, invasive wave intensity and noninvasive wave intensity waveforms for the baseline model in the right common carotid (left) and right brachial (right) arteries. The S wave results from systolic contraction; the R wave is a reflection from a distal site of the S wave; the D wave results from diastolic relaxation; and the V wave results from the closure of the aortic valve, which is in turn responsible for the incisura. The origin of the C1 wave remains to be established definitively, though Curtis et al. 2 have attributed it to reflections which travel back through the aorta and into the suprathoracic region; this wave presents differently in the carotid and the brachial arteries.

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  Figure 4.. Ensemble-averaged waveforms for the right common carotid artery.

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  Figure 5.. Ensemble-averaged waveforms for the right brachial artery. The wave intensity waveforms of the youngest subjects present a large C1 wave; in this case, it is a forward travelling decompression wave which decelerates flow and results in a relatively large backflow.

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  Figure 6.. Ensemble-averaged waveforms for the right radial artery. The pulse wave velocity from the lnDU -loop introduces slight errors when separating forward and backward waves with the noninvasive formulation in the youngest age group.

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  Figure 7.. Ensemble-averaged waveforms for the thoracic aorta.

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  Figure 8.. Correlation coefficients between the dI and n dI waveforms for three arteries in the baseline model. All are very close to 1, indicating that the two wave intensities are similar as expected. The greatest variation occurs in the carotid and radial arteries; this is indicative of the significant effect of viscoelasticity, as these arteries were modelled to have the largest wall viscosities.

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  Figure 9.. Comparison of metrics derived from invasive and noninvasive wave intensity analysis averaged across all subjects for different arteries. The biggest differences are for the reflection coefficients and delays in the common carotid and radial arteries. The systolic wave energy ratio and peak ratio show excellent agreement for all arteries.

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  Figure 10.. Comparison of waveforms and metrics for invasive and noninvasive wave intensity analysis, calculated with ideal pulse wave velocities and stratified by age and artery. The biggest differences between the two formulations are for the reflection coefficients and delays in the common carotid and for the start delays in the radial: in all these cases, the two WIs show different trends as age increases.

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  Figure 11.. Comparison of waveforms and metrics for invasive and noninvasive wave intensity analysis, calculated with loop-derived pulse wave velocities and stratified by age and artery.

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  Figure 12.. The effect of increasing α on the pressure–diameter relationship for the ascending aorta (left), together with the pressure–diameter relationships for the right common carotid (middle) and right radial (right) arteries, with the wave speeds of the separate tube laws scaled to match at the initial pressure. Note that the case α=0.5 gives an almost identical relationship to the Voigt-type law as expected.