Arterial flow based transfer function and ascending aorta pressure waveform estimation

Hypertension has been recognized as a leading cause of cardiovascular diseases. It is principally determined by the amount of the blood ejected by the heart and the properties of the receiving arteries. There is a strong correlation of a reduction in large artery compliance and high blood pressure. Thus, it is important to identify the causative factors that contribute to the severity of hypertension in terms of blood pressure, flow and mechanical properties of arteries. Numerous methods have been used to measure peripheral arterial blood pressure. As pressure waveform travels away from heart, it is amplified because of increased elastic stiffness which gives rise to wave reflections. As a result, peripheral pressure cannot accurately describe cardiovascular events. On the other hand, central aortic pressure is a much better predictor, but it can only be measured directly with an invasive catheter. For this reason, several pressure-based generalized transfer function methods have been proposed. In this thesis, a novel flow-based generalized transfer function is established. This new method is tested using carotid flow waveform as an input to predict ascending aortic flow. Additionally a three element windkessel model was used to predict ascending aortic pressure. Results show good correspondence of predicted ascending aortic flow and pressure. The present approach can be effectively applied in clinical situations where either peripheral arterial flow or ascending aortic flow noninvasively obtained by Doppler ultrasound can be used to obtain ascending aortic pressure. The derived aortic pressure waveform can then be further analyzed in terms of large artery compliance and systolic pressure augmentation, both critical in determining the severity of hypertension.