Assessment of pressure wave reflection: getting the timing right!

Assessment of timing and magnitude of wave reflection is ideally based on wave separation analysis (WSA). In clinical practice, however, waveform analysis (WFA) is often used to study wave reflection, with different coexisting approaches to assess 'landmarks' on the waveform which are indicative for return of the reflected wave. The aim of this work was to compare WSA and WFA. Data were obtained from 2132 subjects (1093 women) aged between 35 and 56 and free from overt cardiovascular disease. Carotid pressure and aortic flow waveforms, and carotid-femoral pulse wave velocity were measured non-invasively. WSA yielded the timing of return of reflected wave (T(f-b)), the ratio of forward and backward pressure wave (P(b)/P(f)), and the effective length of the arterial tree (L(eff)). WFA resulted in identification of the shoulder (T(sho)) or inflection point (T(inf)) as landmark points, with subsequently derived augmentation index and L(eff) (AIx(sho) and L(eff,sho), AIx(inf) and L(eff,inf), respectively). (i) Neither T(inf) nor T(sho) corresponded with the timing obtained from WSA. (ii) Measurements of L(eff) were found to decrease with age (conforming with current physiological insights) whilst L(eff,inf) was found to increase with age in women, and mixed results were obtained for L(eff,sho). (iii) Both AIx(inf) and AIx(sho) showed a persistent gender difference which was not present in P(b)/P(f). Using the pressure at T(f-b) to calculate AIx, the systematic gender difference in AIx(f-b) was greatly reduced. Analysis of pressure wave reflection is optimally based on measurement of pressure and flow, rather than on waveform analysis alone.