10.03 Early Reflection Observed in the Pulse Wave in the Common Carotid Artery Originates from Either the Circle of Willis or the Capillary Bed of the Facial Musculature

Abstract

Introduction

Arterial wave reflections augment pulse pressures at heart level and manifest as an inflection point in the blood pressure waveform. However, the origin of reflection is still partly unresolved and can not be derived using the waveform from a single location.

Method

Two distension waveforms, spaced at 16.4mm, were simultaneously obtained in the left CCA of 12 young subjects with dual M-line ultrasound. The second derivatives of the distension waveforms were calculated to identify the opening of the aortic valve (AVO) and the inflection point before systolic peak pressure (IP). The time-delay (ΔT) between both time points, either AVO or IP, in the proximal and distal waveform was calculated to obtain the direction of propagation.

Results

Mean time difference between AVO and IP was 38 ± 8ms. There was a significant time difference in AVO (p < 0.0001) and IP (p = 0.0012) between proximal and distal waveform. AVO had a positive delay ΔT_AvO = 3.3 ± 1.0ms. In contrast IP had a negative delay ΔTI_P = –3.6 ± 3.1ms.

Discussion

Time-delay of AVO and IP are comparable but opposite in sign. Measurements were performed on the CCA, which is a small straight arterial segment without branches, therefore the effect of dispersion or tapering can be ignored and the direction of propagation of IP can only be explained by reflections. Using the time difference between AVO and IP and assuming constant wave-speed, the distance between reflection and measurement site was estimated at 12cm, pointing at the circle of Willis or the capillary bed of the facial musculature as distal reflection sites.