Abstract 17711: Can Aortic Wave Reflecting Site be Estimated from the Early Systolic Shoulder?
Effects of wave reflection on the aortic pressure wave can be estimated from augmentation of pressure in late systole. Onset is gauged as time from wavefoot to early systolic shoulder; this is taken to represent peak of the aortic flow waveform for non-invasive measurement of aortic characteristic impedance. The initial shoulder at time T1 is often followed by a second (upward) component with concavity to the left (Tr) (figure a). On the basis of such timing and with knowledge of increasing carotid-femoral pulse wave velocity (CFPWV) with age, Mitchell et al (Hypertension 2004;43:1239) estimate that the site of wave reflection in the aorta moves distally, below the diaphragm as age increases, and see this as a compensating mechanism to reduce effects of wave reflection on the heart and brain during systole. In a cohort of 1505 subjects in a cardiac outpatient clinic, 9543 aortic pressure waves generated from radial artery tonometry using SphygmoCor, the initial shoulder (T1) and the onset of secondary rise (Tr) decreased slightly with age but largely overlaid each other (figure b). When Tr was expressed as a function of CFPWV, there was a weak relationship below PWV of 10 m/s (p<0.05, R2=0.1), but no relationship above 10 m/s (p<0.05,R2=0.0), with Tr remaining relatively constant at >140 msec (figure c). Our problem was in identifying Tr and T1 from each other, or at all when Tr was ≤140 msec. This period, corresponds to predicted return of wave reflection in older persons with stiffened aorta, together with onset of the first component, hence convexity and concavity would overlie - with each cancelling the other and neither able to be identified. Our explanation hence is that onset of wave reflection, as Tr, is bound to be inaccurate when CFPWV is fast (>10 m/s) and hence Tr short (<130 msec). On the basis of these findings, we cannot support distal movement of a functionally discrete reflecting site from mid to distal aorta with age.
- © 2012 by American Heart Association, Inc.