06.07 Evaluation of a Method of Wave Reflection Assessment Via Triangular Flow Wave Approximation

Abstract

Introduction

Wave reflections affect the aortic pressure and flow wave and play a role in systolic hypertension. Accurate quantification of pressure wave reflection requires separation of pressure in its forward (P_f) and backward (P_b) components, which requires aortic flow measurement. This limitation can be overcome by replacing the unknown flow wave by a triangular estimate of arbitrary amplitude, as recently proposed. We verified this technique using pressure and flow data measured in the Asklepios study (>2500 participants, 35 to 55 years).

Method

Wave separation analysis using measured pressure and flow yielded the reference reflection magnitude (RM = P_b/P_f). Then, RM was estimated using three triangular approximations of the flow wave, each with duration equal to the ejection time but with peak at (i) the shoulder point of the pressure wave (F^tSP);(ii) 30% of the ejection time (F^t30) and (iii) the moment of real peak flow (F^tQm).

Results

The correlation between measured and estimated RM’s was highly significant (P<0.001) but overall disappointingly poor (R² = 0.21 to 0.25), the highest correlation coefficient being obtained when using (F^tQm). Overall, the approximation overestimated RM_ref by 10 to 12%. Interestingly, we found the accuracy of all estimations to depend highly on age (P<0.001), with the accuracy improving with age.

Conclusion

In healthy middle-aged subjects, quantification of wave reflection by estimating a triangular flow wave shows limited accuracy, even when timing of the peak is obtained directly from the flow waveform. This seems to imply that the triangular shape may be a too simple waveform approximation in this population.