Fig. 4.

Theoretical (red lines) and estimated pulse wave speed with distance in 1 cm increments from the aortic root (x=0) to the end of the left anterior tibial artery, through the same segments as in Fig. 3. Estimated values calculated using the PU-loop, $\ln \mathit{DU}$-loop, QA-loop and sum-of-squares (${\sum }^2$) methods with the pulse waveforms from the (a,b) purely elastic and (c,d) visco-elastic normal models and the (e,f) well-matched model. Estimated values using the D²P-loop method are not shown, since they cannot be distinguished from the theoretical values in the scale of the figures. Note the different scales of c in the left and right figures, and the different theoretical values for the normal and well-matched models. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)