Estimation of aortic and left ventricular (LV) pressure usually requires measurements that are difficult to obtain during the imaging required to obtain concurrent LV dimensions essential for determination of LV mechanical properties. We describe a novel method for deriving aortic pressure from the aortic flow velocity. The target pressure waveform is divided into an early systolic upstroke, determined by the water hammer equation, and a diastolic decay equal to that in the peripheral arterial tree, interposed by a late systolic portion described by a second-order polynomial constrained by conditions of continuity and conservation of mean arterial pressure. Pulse wave velocity (PWV, obtainable during imaging), mean arterial pressure, diastolic pressure and diastolic decay are required inputs for the algorithm. Pressure and flow velocities were simulated using a simplified 1-D tube model and experimental data were acquired through a pressure/Doppler flow velocity transducer placed in the ascending aorta in 18 patients (mean±SD, age: 61.8±10.3 years, aortic BP: 136±23/73±13 mmHg). PWV, mean and diastolic pressures and diastolic decay were taken from model parameters or calculated from reference pressures/flows (i.e. were assumed to be known). Estimated pressure waveforms showed excellent agreement with reference pressures for both the simulated and experimental data (mean±SD root mean square error, 0.7±0.1 mmHg and 2.4±1.0 mmHg for numerically simulated and experimental data respectively; peak systolic pressure, mean±SD, 0.4±0.6 mmHg and 1.4±2.0 mmHg for numerically simulated and experimental data respectively). This is the first non-invasive derivation of aortic pressure based on phenomenon occurring directly in the ascending aorta.
- central blood pressure
- aortic flow velocity
- pulse wave velocity
- left ventricle
- Copyright © 2015, American Journal of Physiology - Heart and Circulatory Physiology