Measurement of Inter and Intra-cycle Variations in Local Pulse Wave Velocity from Forward Travelling Pulse Waves

The local PWV and its pressure-dependent changes within a cardiac cycle are potential biomarkers for cardiovascular risk stratification. However, the influence of pulse wave reflections hampers the accuracy of local PWV measurements. We propose a method to measure the pressure-dependent variations in local PWV after minimizing the effect of wave reflections. The technique measures the pulse transit time between two simultaneously acquired and processed forward-running pulse waveforms obtained after wave separation analysis (WSA). A cross-sectional in-vivo study was conducted on 57 human participants (22 female) to compare the inter and intra-cycle variations in PWV based on pulse transit-time obtained from two measured pulse waves and two forward-travelling pulse waves. The reference PWV for comparison was obtained using Bramwell-Hill equations. The required signals proximal and distal diameter waveforms from the carotid artery, simultaneously with carotid tonometry were acquired using an in-house developed bi-modal arterial probe. The carotid blood flow for WSA was recorded using an ultrasound imaging system. The reliability of measuring PWV was improved after WSA (coefficient of variation improved from 25% to 10% for PWV at the systolic level). The average PWV obtained before WSA and after WSA at diastolic levels were comparable with the reference PWV
$(\mathbf{p} > \mathbf{0.05})$
. The average PWV obtained before WSA and after WSA at systolic levels were significantly different
$(\mathbf{p} < \mathbf{0.001})$
; however, the PWV after WSA at systole level was comparable with the reference PWV
$(\mathbf{p} > \mathbf{0.05})$
. The group average carotid pulse pressure derived from the mean values of PWV within the cardiac cycle, obtained after WSA
$(\mathbf{25.90}\pm \mathbf{5.88}\ \mathbf{mmHg})$
, was statistically
$(\mathbf{p} > \mathbf{0.05})$
comparable to the carotid pulse pressure obtained using carotid tonometry-calibrated with brachial mean and diastolic blood pressure
$(\mathbf{26.74}\pm \mathbf{4.72}\ \mathbf{mmHg})$
. Therefore, this proposed method has the potential to improve the measurement reliability of local PWV, aiding the ongoing global efforts of cardiovascular risk management.