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(Hypertension. 2009;53:142.)
© 2009 American Heart Association, Inc.

Original Articles

Evaluation of Noninvasive Methods to Assess Wave Reflection and Pulse Transit Time From the Pressure Waveform Alone

Jan G. Kips; Ernst R. Rietzschel; Marc L. De Buyzere; Berend E. Westerhof; Thierry C. Gillebert; Luc M. Van Bortel; Patrick Segers

From the Cardiovascular Mechanics and Biofluid Dynamics (J.G.K., P.S.), IBiTech, and Department of Pharmacology (J.G.K., L.M.V.B.), Ghent University, Ghent, Belgium; Department of Cardiovascular Diseases (E.R.R., M.L.D.B., T.C.G.), Ghent University Hospital, Ghent, Belgium; and BMEYE Cardiovascular Monitoring Company (B.E.W.), Academic Medical Center-University of Amsterdam, Amsterdam, The Netherlands.

Correspondence to Jan G. Kips, Cardiovascular Mechanics and Biofluid Dynamics, IBiTech, Ghent University, De Pintelaan 185, B-9000 Gent, Belgium. E-mail Jan.Kips{at}UGent.be

Accurate quantification of pressure wave reflection requires separation of pressure in forward and backward components to calculate the reflection magnitude as the ratio of the amplitudes backward and forward pressure. To do so, measurement of aortic flow in addition to the pressure wave is mandatory, a limitation that can be overcome by replacing the unknown flow wave by an (uncalibrated) triangular estimate. Another extended application of this principle is the derivation of aortic pulse transit time from a single pulse recording. We verified these approximation techniques for reflection magnitude and transit time using carotid pressure and aortic flow waveforms measured noninvasively in the Asklepios Study (>2500 participants; 35 to 55 years of age). A triangular flow approximation using timing information from the measured aortic flow waveform yielded moderate agreement between reference and estimated reflection magnitude (R²=0.55). Approximating the flow by a more physiological waveform significantly improved these results (R²=0.74). Aortic transit time was assessed using pressure and measured or approximated flow waveforms, and results were compared with carotid-femoral transit times measured by Doppler ultrasound. Agreement between estimated and reference transit times was moderate (R²<0.29). Both for reflection magnitude and transit time, agreement between reference and approximated values further decreased when the approximated flow waveform was obtained using timing information from the pressure waveform. We conclude that, in our Asklepios population, results from pressure-based approximative methods to derive reflection magnitude or aortic pulse transit time differ substantially from the values obtained when using both measured pressure and flow information.

Key Words: hypertension • blood pressure measurement/monitoring • hemodynamics • arterial stiffness • wave reflection • pulse wave velocity