5 Does Behaviour of the Reflected Wave in Humans Support the Prevailing Explanation of the Arterial Pressure Waveform?

Background: It is widely believed that changes in the magnitude and timing of reflected waves reaching the heart result in deleterious cardiovascular effects. Inherent in this is the assumption that waves propagate well in the backward direction. There is limited information regarding retrograde travel of the reflected wave from an imposed occlusion. We investigated this. Methods: In this study, 20 subjects (age 31–83 years), underwent invasive measurement of pressure & Doppler velocity with sensor-tipped intra-arterial wires placed in the aorta, iliac artery and femoral artery. An external cuff was inflated to occlude one femoral artery, creating a site of total reflection and the effect of this assessed. Separated wave intensity analysis was used to identify and quantify incident and reflected waves. Wave reflection index (WRI) expresses the backward compression wave as a percentage of the incident forward compression wave. Results: The additional reflection (evident by statistically significant increase in WRI and earlier arrival of the reflected wave) generated in the femoral artery by femoral occlusion was not visible in the proximal aorta. Furthermore, the reflected wave in the proximal aorta occurred in systole in all subjects, much earlier than is widely proposed. Conclusion: A reflection arising from an occlusion is wholly attenuated by the time it reaches the proximal aorta. This lack of retrograde travel could account for the limited reflection in the proximal aorta and prompts review of our understanding of the mechanisms underlying blood pressure augmentation.