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

Abstract

Abstract-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 (Ͼ2500 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 (R 2 ϭ0.55). Approximating the flow by a more physiological waveform significantly improved these results (R 2 ϭ0.74). 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 (R 2 Ͻ0.29). 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 Ⅲ blood pressure measurement/monitoring Ⅲ hemodynamics Ⅲ arterial stiffness Ⅲ wave reflection Ⅲ pulse wave velocity T he pressure pulse can be considered as the composite of a forward pressure wave, traveling from the heart to the periphery, and of a reflected pressure wave, traveling backward toward the heart. Early return of this reflected wave boosts (central) systolic blood pressure, increasing the load on the heart and boosting the amplitude of the pressure pulse, factors that have been shown to increase cardiovascular risk. [1][2][3][4] Therefore, analysis of pulse wave velocity and pressure wave reflection have been points of clinical interest for many years now.Several methods to quantify wave reflection emerged, 5 the most widespread probably being the augmentation index (AIx). 6,7 AIx is a parameter based on analysis of the pressure waveform and expresses the ratio of augmented pressure (attributed to wave reflection) to pulse pressure. However, because several factors influence its value, 8 -12 AIx might not be the most appropriate parameter for an accurate quantification of the magnitude of wave reflection. 13 More accurate methods to assess wave reflection are based on wave separation analysis....

Arterial Stiffness and Hypertension

“…The use of a triangular estimate of flow also circumvents the need for additional arterial Doppler measurements, although the accuracy of this approach has been called into question, and more physiologically shaped estimates of flow have been proposed. 28 As well as providing an estimate of reflection magnitude, 28 these techniques have been used to estimate carotid-femoral transit time, albeit with only a modest correlation. 28,29 However, it has been shown that, because there is an uncertain time delay introduced at the reflection site, it is not possible to know the true pulse transit time; thus, the site of reflection (and, hence, wave velocity) cannot be accurately determined.…”

Vascular and central hemodynamic changes following exercise-induced heat stress

“…22 This technique is widely accepted 14,23 and has been described in detail previously. 22,24 A wave reflection index (RIx) was calculated by dividing Pb by Pf as a measure of reflection magnitude (i.e. wave reflection magnitude relative to forward wave magnitude).…”

Ventricular–vascular coupling in hypertension

“…Application of this model in a separate group of 44 patients provided good agreement. 44 Data from the large population (>2500 patients, 35-55 years old) of the ASKLEPIOS Study, 45 however, did not confirm the accuracy of this approach when compared with Doppler aortic flowmetry. Moreover, derived measures of wave reflection showed only modest correlation with reference values.…”

“…Moreover, derived measures of wave reflection showed only modest correlation with reference values. 45 According to these data, the simplified approach for flow wave reconstruction (the 'triangular approximation') could not be recommended for assessing pressure/flow relationship.…”