Background: Local Pulse Wave Velocity (LPWV) and Wave Intensity (WI) are used to assess arterial stiffness and the arrival time of reflected waves; indices of clinical importance. We present a new non-invasive analysis which directly uses flow velocity (U) and arterial diameter (D) measurements for the determination of LPWV and WI.

Methods: From the water hammer equation it can be shown that LPWV=D2dU±dD± where dU and dD are the changes in U and D, and ± indicates the forward and backward directions. The separation of WI can also be determined using WI±=±14(D/2c)(dD±D2cdU)2, where c is LPWV. We studied 28 patients (58±15 years, 21 male) with good systolic function (EF>55%) and no valve disease. We measured U and D in the left carotid artery using Doppler ultrasound and a wall tracking system (Aloka, SSD-5500). ECG was also recorded and data were sampled at 1kHz.

Results: LPWV in patients > 50 years (n=11) were higher by 20% (p < 0.05) than in patients < 50 years. Reflected waves in patients > 50 years arrived earlier by 35% (p < 0.05) than in patients <50 years. Neither the size of reflected waves nor the forward compression and expansion wave differed significantly between the two age groups.

Conclusions: Results of the new technique are in agreement with other approaches for determining LPWV and WI. The new technique offers the possibility of studying arterial sites that are not accessible by applanation tonometery, and does not assume a linear relationship between arterial diameter and arterial pressure.