Pulse Wave Ultrasound Manometry (PWUM): Measuring central blood pressure non-invasively

As it has been widely established using invasive methodologies, central blood pressure (CBP) has a strong clinical relevance. Despite its significance, CBP is particularly challenging to measure in standard clinical practice. Pulse-Wave-based Ultrasound Manometry (PWUM) is a simple-to-use, non-invasive ultrasound-based method that combines Pulse Wave Imaging (PWI) and vessel diameter measurements for the quantitative regional and noninvasive measurement of the central pulse pressure. The objective of this study is to assess the feasibility of the proposed method in human subjects and to compare the PWUM to non-invasive arterial tonometry. Arterial wall displacements were estimated using radiofrequency (RF) ultrasound signals at high frame rates (248-392 Hz) using a Sonix Touch (Ultrasonix, Burnaby, Canada) system at 3.3 MHz. This allowed for (1) the estimation of the Young´s modulus of the arterial wall, based on an image-guided measurement of the Pulse Wave Velocity (PWV) and the Moens-Korteweg equation, and (2) the estimation of the vessel distension waveform over the entire cardiac cycle. The combination of these two measurements allowed for the computation of the pressure waveform under the assumption of linear elasticity. The PWUM method was tested on the abdominal aorta of 11 healthy subjects (age 35.7± 16 y.o.). The PWUM pulse pressure measurements were compared to those obtained by radial applanation tonometry that uses a commercial system (SphygmoCor, Company, location) that estimates the pulse pressure at the thoracic aorta through a transfer function approach based on peripheral (carotid and radial) pressure measurements. All subjects were tested with both PWUM and tonometry to evaluate the performance of the former. The average intra-subject variability of the pulse pressure amplitude was found to be equal to 4.2 mmHg, demonstrating good reproducibility of the method. Excellent correlation was found between the waveforms obtained by PWUM and th- se obtained by tonometry in all subjects (0.94 <; r <; 0.98). A significant bias of 4.7 mmHg was found between PWUM and tonometry. The feasibility of the PWUM method was demonstrated in this study. PWUM is a simple, non-invasive and regional ultrasound-based method that provides a direct measurement of the pulse pressure waveform at the imaged location, and may offer therefore the capability of estimating the pulse pressure at different arterial sites. This can constitute an important alternative to current, clinically used central pressure methodologies that are either invasive (catheterization) or incur the solution of an inverse problem based on several assumptions on geometry and boundary conditions. Future developments include the validation of the method against invasive estimates, application to other central arteries, in the presence and absence of cardiovascular disease.