PWV measurement influenced by distance between two recording sites.

To the Editor: We have read the recent letter by Hermeling et al. entitled “Potentials and Pitfalls of Local PWV Measurements,”1 discussing the advantages and challenges for local pulse wave velocity (PWV) measurements. The letter was in reference to an article by Vappou et al. regarding pulse wave imaging measurement of arterial stiffness in vivo.2 In the common carotid artery, due to the susceptibility of the systolic foot in the local PWV measurement, the authors suggest the dicrotic notch as a new time reference point. However, how strong the interference influence on the foot-to-foot PWV and how the distance of the recording sites affects the PWV remain unknown. Therefore, we tested the reliability of the foot-to-foot PWV when the periodic water input was pumped into simulated T-tubes. The frequency of the input was set to match the fundamental natural frequency of the T-tube to simulate the in vivo condition.3 The simulation system has evolved from our previous study4 in 1991 and has been improved according to the theoretical model in 2008.5 We chose five uniform latex tubes all with the length of 180 cm and similar physical dimensions, but different Peterson’s elastic modulus. The PWV measurements were performed to study the correlation with the arterial stiffness (Table 1). We found that the linear correlation between the foot-to-foot PWV and the tube stiffness is significant (r > 0.7, P < 0.1) for all regions. However, the longer the region of the measurement is, the higher the correlation between the foot-to-foot PWV and the elasticity of the tube is shown. The result confirms the in vivo observation by Hermeling et al.1 The simulation experiment also reveals that long-distance PWV, such as carotid-femoral PWV, can reflect the arterial stiffness well in spite of the change in the waveform.