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 ( Tf-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,L- sho, AIx(inf) and L-eff,L- 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,L- 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 Tf-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.