Robust and practical non-invasive estimation of local arterial wave speed and mean blood velocity waveforms

TY - JOUR

T1 - Robust and practical non-invasive estimation of local arterial wave speed and mean blood velocity waveforms

AU - Kowalski, Remi

AU - Beare, Richard

AU - Willemet, Marie

AU - Alastruey, Jordi

AU - Smolich, Joseph J

AU - Cheung, Michael M H

AU - Mynard, Jonathan P

N1 - © 2017 Institute of Physics and Engineering in Medicine.

PY - 2017/11/1

Y1 - 2017/11/1

N2 - OBJECTIVE: Local arterial wave speed, a surrogate of vessel stiffness, can be estimated via the pressure-velocity (PU) and diameter-velocity (ln(D)U) loop methods. These assume negligible early-systolic reflected waves (RWes) and require measurement of cross-sectionally averaged velocity (U_mean), which itself is a valuable quantity related to volumetric blood flow. However, RWes may not always be negligible and routine Doppler ultrasound typically provides maximum velocity waveforms or estimates of mean velocity subject to various errors (U_raw). This study investigates how these issues affect wave speed estimation and explores more robust methods for obtaining local wave speed and Umean. Approach. Using aortic phase-contrast MRI (PCMRI, n=34) and a simulated virtual cohort (n=3325), we assessed errors in calculated wave speed caused by RWes and use of U_raw rather than true U_mean. By combining PU_raw and ln(D)U_raw loop wave speed values, (i) a corrected wave speed (ln(D)P), insensitive to RWes and velocity errors, was derived; and (ii) a novel method for estimating U_mean from U_raw was proposed (where U_raw can be any scaled version of U_mean). Main results. Proof-of-principle was established via PCMRI data and in the ascending aorta, carotid, brachial and femoral arteries of the virtual cohort, with acceptably low wave speed and U_mean errors obtained even when local pressure was estimated from diameter and mean/diastolic brachial pressures. Significance. Given a locally-measured diameter waveform and brachial cuff pressures, (i) the velocity- and RWes-independent ln(D)P method can be applied non-invasively and is likely more robust than ln(D)U and PU loop methods; and (ii) U_mean can be estimated from routinely-acquired U_raw.

AB - OBJECTIVE: Local arterial wave speed, a surrogate of vessel stiffness, can be estimated via the pressure-velocity (PU) and diameter-velocity (ln(D)U) loop methods. These assume negligible early-systolic reflected waves (RWes) and require measurement of cross-sectionally averaged velocity (U_mean), which itself is a valuable quantity related to volumetric blood flow. However, RWes may not always be negligible and routine Doppler ultrasound typically provides maximum velocity waveforms or estimates of mean velocity subject to various errors (U_raw). This study investigates how these issues affect wave speed estimation and explores more robust methods for obtaining local wave speed and Umean. Approach. Using aortic phase-contrast MRI (PCMRI, n=34) and a simulated virtual cohort (n=3325), we assessed errors in calculated wave speed caused by RWes and use of U_raw rather than true U_mean. By combining PU_raw and ln(D)U_raw loop wave speed values, (i) a corrected wave speed (ln(D)P), insensitive to RWes and velocity errors, was derived; and (ii) a novel method for estimating U_mean from U_raw was proposed (where U_raw can be any scaled version of U_mean). Main results. Proof-of-principle was established via PCMRI data and in the ascending aorta, carotid, brachial and femoral arteries of the virtual cohort, with acceptably low wave speed and U_mean errors obtained even when local pressure was estimated from diameter and mean/diastolic brachial pressures. Significance. Given a locally-measured diameter waveform and brachial cuff pressures, (i) the velocity- and RWes-independent ln(D)P method can be applied non-invasively and is likely more robust than ln(D)U and PU loop methods; and (ii) U_mean can be estimated from routinely-acquired U_raw.

KW - Journal Article

U2 - 10.1088/1361-6579/aa8de3

DO - 10.1088/1361-6579/aa8de3

M3 - Article

C2 - 28930095

SN - 0967-3334

VL - 38

SP - 2081

EP - 2099

JO - Physiological Measurement

JF - Physiological Measurement

IS - 11

ER -