Despite clear associations with adverse cardiovascular outcomes, the mechanisms driving aortic pressure propagation remain incompletely defined. The reservoir-wave approach has been proposed as a representative model of central aortic pressure generation however its application at differing aortic locations has not been investigated.Design and method:
We analysed invasively acquired aortic pressure waveforms from 40 patients undergoing clinically indicated catheterisation. Waveforms were acquired at the level of the ascending aorta, transverse aortic arch, diaphragm, renal arteries and aortic bifurcation using a solid-state transducer. Reservoir-wave analysis was performed according to previously described techniques to determine reservoir and excess pressures and systolic and diastolic rate constants (ks and kd). ks is inversely related to the product of aortic characteristic impedance and total arterial compliance while kd is inversely related to the product of systemic arterial resistance and arterial compliance and is the reciprocal of the diastolic time constant. Repeated measures 1-way-ANOVA with Dunnett's test for multiple comparisons was used to compare parameters at the 5 aortic sites.Results:
Systolic blood pressure increased predictably from the ascending aorta to the bifurcation, whilst diastolic blood pressure remained constant. ks (corresponding to characteristic impedance) increased while kd decreased with distal progression. The excess pressure integral increased with distal progression (P < 0.001) whereas the reservoir pressure integral decreased and maximal reservoir pressure did not vary. The timing of peak reservoir pressure (relative to the initial systolic upstroke) decreased progressively from the aortic root (P < 0.001) whilst the timing of maximal excess pressure did not change.Conclusions:
The increase in maximum excess pressure (probably wave related) between the ascending aorta and bifurcation and the constant time to peak excess pressure suggests that wave transmission is relatively more important in determining distal conduit arterial pressures. The decrease in ks with distal progression is consistent with gradually rising impedance whilst the increase in kd is suggestive of progressively decreasingly compliance. These findings support previous data suggesting a relatively minor role for wave reflection in determining the amplitude of the aortic pressure waveform.