title: Noninvasive calculation of the aortic blood pressure waveform from the flow velocity waveform: a proof of concept.
abstract: Estimation of aortic and left ventricular (LV) pressure usually requires measurements that are difficult to acquire 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, which can be obtained through imaging), mean arterial pressure, diastolic pressure, and diastolic decay are required inputs for the algorithm. The algorithm was tested using 1) pressure data derived theoretically from prespecified flow waveforms and properties of the arterial tree using a single-tube 1-D model of the arterial tree, and 2) experimental data acquired from a pressure/Doppler flow velocity transducer placed in the ascending aorta in 18 patients (mean ± SD: age 63 ± 11 yr, aortic BP 136 ± 23/73 ± 13 mmHg) at the time of cardiac catheterization. For experimental data, PWV was calculated from measured pressures/flows, and mean and diastolic pressures and diastolic decay were taken from measured pressure (i.e., were assumed to be known). Pressure reconstructed from measured flow agreed well with theoretical pressure: mean ± SD root mean square (RMS) error 0.7 ± 0.1 mmHg. Similarly, for experimental data, pressure reconstructed from measured flow agreed well with measured pressure (mean RMS error 2.4 ± 1.0 mmHg). First systolic shoulder and systolic peak pressures were also accurately rendered (mean ± SD difference 1.4 ± 2.0 mmHg for peak systolic pressure). This is the first noninvasive derivation of aortic pressure based on fluid dynamics (flow and wave speed) in the aorta itself.
authors.affiliation: Department of Clinical Pharmacology, King's College London British Heart Foundation Centre, St. Thomas' Hospital, London, United Kingdom; Division of Imaging Sciences and Biomedical Engineering, King's College London, St. Thomas' Hospital, London, United Kingdom; and.
authors.forename: Samuel
authors.initials: S
authors.lastname: Vennin
authors.affiliation: Department of Clinical Pharmacology, King's College London British Heart Foundation Centre, St. Thomas' Hospital, London, United Kingdom;
authors.forename: Alexia
authors.initials: A
authors.lastname: Mayer
authors.affiliation: Department of Clinical Pharmacology, King's College London British Heart Foundation Centre, St. Thomas' Hospital, London, United Kingdom;
authors.forename: Ye
authors.initials: Y
authors.lastname: Li
authors.affiliation: Department of Clinical Pharmacology, King's College London British Heart Foundation Centre, St. Thomas' Hospital, London, United Kingdom;
authors.forename: Henry
authors.initials: H
authors.lastname: Fok
authors.affiliation: Department of Cardiology, Guy's and St. Thomas' Foundation Trust, London, United Kingdom.
authors.forename: Brian
authors.initials: B
authors.lastname: Clapp
authors.affiliation: Division of Imaging Sciences and Biomedical Engineering, King's College London, St. Thomas' Hospital, London, United Kingdom; and.
authors.forename: Jordi
authors.initials: J
authors.lastname: Alastruey
authors.affiliation: Department of Clinical Pharmacology, King's College London British Heart Foundation Centre, St. Thomas' Hospital, London, United Kingdom; phil.chowienczyk@kcl.ac.uk.
authors.forename: Phil
authors.initials: P
authors.lastname: Chowienczyk
mesh_terms: D000368:Aged; D001011:Aorta / Q000502:physiology*; D001783:Blood Flow Velocity; D001794:Blood Pressure; D006801:Humans; D008875:Middle Aged; D008955:Models, Cardiovascular
keywords: aortic flow velocity; central blood pressure; hypertension; left ventricle; pulse wave velocity