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(Hypertension. 2006;48:595.)
© 2006 American Heart Association, Inc.

Original Articles

Quantification of Wave Reflection in the Human Aorta From Pressure Alone

A Proof of Principle

Berend E. Westerhof; Ilja Guelen; Nico Westerhof; John M. Karemaker; Alberto Avolio

From the BMEYE (B.E.W., I.G.), Amsterdam, The Netherlands; Physiology (N.W.), Institute for Cardiovascular Research-Vrije University, VU University Medical Center, Amsterdam, The Netherlands; Physiology (J.M.K.), Academic Medical Centre, University of Amsterdam, The Netherlands; and the Graduate School of Biomedical Engineering (A.A.), University of New South Wales, Sydney, Australia.

Correspondence to Berend E. Westerhof, BMEYE BV, Academic Medical Centre, Suite K2-245, University of Amsterdam, Meibergdreef 9, NL-1105 AZ Amsterdam, The Netherlands. E-mail berend.westerhof{at}bmeye.com

Wave reflections affect the proximal aortic pressure and flow waves and play a role in systolic hypertension. A measure of wave reflection, receiving much attention, is the augmentation index (AI), the ratio of the secondary rise in pressure and pulse pressure. AI can be limiting, because it depends not only on the magnitude of wave reflection but also on wave shapes and timing of incident and reflected waves. More accurate measures are obtainable after separation of pressure in its forward (P_f) and reflected (P_b) components. However, this calculation requires measurement of aortic flow. We explore the possibility of replacing the unknown flow by a triangular wave, with duration equal to ejection time, and peak flow at the inflection point of pressure (F^tIP) and, for a second analysis, at 30% of ejection time (F^t30). Wave form analysis gave forward and backward pressure waves. Reflection magnitude (RM) and reflection index (RI) were defined as RM=P_b/P_f and RI=P_b/(P_f+P_b), respectively. Healthy subjects, including interventions such as exercise and Valsalva maneuvers, and patients with ischemic heart disease and failure were analyzed. RMs and RIs using F^tIP and F^t30 were compared with those using measured flow (F^m). Pressure and flow were recorded with high fidelity pressure and velocity sensors. Relations are: RM^tIP=0.82RM^mf+0.06 (R²=0.79; n=24), RM^t30=0.79RM^mf+0.08 (R²=0.85; n=29) and RI^tIP=0.89RI^mf+0.02 (R²=0.81; n=24), RI^t30=0.83RI^mf+0.05 (R²=0.88; n=29). We suggest that wave reflection can be derived from uncalibrated aortic pressure alone, even when no clear inflection point is distinguishable and AI cannot be obtained. Epidemiological studies should establish its clinical value.

Key Words: aorta • blood flow • blood flow velocity • blood pressure • pulse

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