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Abstract: As an emerging flow-mapping tool that can penetrate deep into optically opaque media such as human tissue, ultrasound imaging velocimetry has promise in various clinical applications. Previous studies have shown that errors occur in velocity estimation, but the causes have not been well characterised. In this study, the error in velocity estimation resulting from ultrasound beam sweeping in image acquisition is quantitatively investigated. The effects on velocity estimation of the speed and direction of beam sweeping relative to those of the flow are studied through simulation and experiment. The results indicate that a relative error in velocity estimation of up to 20% can be expected. Correction methods to reduce the errors under steady flow conditions are proposed and evaluated. Errors in flow estimation under unsteady flow are discussed. [Copyright &y& Elsevier]

Abstract: Progress in the field of prosthetic cardiovascular devices has significantly contributed to the rapid advancements in cardiac therapy during the last four decades. The concept of mechanical circulatory assistance was established with the first successful clinical use of heart–lung machines for cardiopulmonary bypass. Since then a variety of devices have been developed to replace or assist diseased components of the cardiovascular system. Ventricular assist devices (VADs) are basically mechanical pumps designed to augment or replace the function of one or more chambers of the failing heart. Computational Fluid Dynamics (CFD) is an attractive tool in the development process of VADs, allowing numerous different designs to be characterized for their functional performance virtually, for a wide range of operating conditions, without the physical device being fabricated. However, VADs operate in a flow regime which is traditionally difficult to simulate; the transitional region at the boundary of laminar and turbulent flow. Hence different methods have been used and the best approach is debatable. In addition to these fundamental fluid dynamic issues, blood consists of biological cells. Device-induced biological complications are a serious consequence of VAD use. The complications include blood damage (haemolysis, blood cell activation), thrombosis and emboli. Patients are required to take anticoagulation medication constantly which may cause bleeding. Despite many efforts blood damage models have still not been implemented satisfactorily into numerical analysis of VADs, which severely undermines the full potential of CFD. This paper reviews the current state of the art CFD for analysis of blood pumps, including a practical critical review of the studies to date, which should help device designers choose the most appropriate methods; a summary of blood damage models and the difficulties in implementing them into CFD; and current gaps in knowledge and areas for future work. [Copyright &y& Elsevier]

Abstract: Haemodynamics studies of abdominal aortic aneurysm require data on the velocity in the normal section of the aorta. Centreline velocity waveforms were measured in abdominal aortic aneurysm patients proximal to the aneurysm using spectral Doppler ultrasound. Characteristic points were automatically found on 21 of the waveforms and their parameters were used to create an archetypal centreline velocity waveform. The maximum velocity was 45 ± 13 cm s−1, the minimum velocity was −15 ± 11 cm s−1 and the maximum diastolic velocity was 2.7 ± 4.7 cm s−1. The velocity wave is suitable for use as an input to in vitro or in silico investigations of abdominal aortic aneurysm haemodynamics. (E-mail: kate.fraser@ed.ac.uk) [Copyright &y& Elsevier]

Abstract: B-mode ultrasound (US) images from blood vessels in vivo differ significantly from vascular flow phantom images. Phantoms with acoustic properties more closely matched to those of in vivo arteries may give better images. A method was developed for measuring the speed and attenuation coefficient of US over the range 5 to 9 MHz in samples of sheep aorta using a pulse-echo technique. The times-of-flight method was used with envelope functions to identify the reference points. The method was tested with samples of tissue-mimicking material of known acoustic properties. The tissue samples were stored in Krebs physiologic buffer solution and measured over a range of temperatures. At 37°C, the acoustic speed and attenuation coefficient as a function of frequency in MHz were 1600 ± 50 ms–1 and 1.5 ± 4f 0.94 ± 1.3 dB cm–1, respectively. (E-mail: kate.fraser@ed.ac.uk) [Copyright &y& Elsevier]

Odorant transport is of fundamental and applied importance. Using computational simulations, we studied odorant transport in an anatomically accurate model of the nasal passage of a hagfish (probably Eptatretus stoutii). We found that ambient water is sampled widely, with a significant ventral element. Additionally, there is a bilateral element to olfactory flow, which enters the single nostril in two narrow, laminar streams that are then split prior to the nasal chamber by the anterior edge of the central olfactory lamella. An appendage on this lamella directs a small portion (10–14%) of the overall nasal flow to the olfactory sensory channels. Much of the remaining flow is diverted away from the sensory channels by two peripheral channels. The anterior edge of the central olfactory lamella, together with a jet-impingement mechanism, disperses flow over the olfactory surfaces. Diffusion of odorant from bulk water to the olfactory surfaces is facilitated by the large surface area:volume ratio of the sensory channels, and by a resistance-based hydrodynamic mechanism that leads to long residence times (up to 4.5 s) in the sensory channels. With increasing volumetric flow rate, the rate of odorant transfer to the olfactory surfaces increases, but the efficiency of odorant uptake decreases, falling in the range 2–6%. Odorant flux decreases caudally across the olfactory surfaces, suggesting in vivo a preponderance of olfactory sensory neurons on the anterior part of each olfactory surface. We conclude that the hagfish has a subtle anatomy for locating and capturing odorant molecules. [Display omitted] • The monorhinal hagfish can smell in stereo. • Jet impaction disperses olfactory flow. • Resistance-based hydrodynamic mechanism aids odorant capture. • Only about 10% nasal flow sampled for olfactory purposes. • Odorant capture efficiency comparable to lower range of dog. [ABSTRACT FROM AUTHOR]

Despite decades of technological advancements in blood-contacting medical devices, complications related to shear flow-induced blood trauma are still frequently observed in clinic. Blood trauma includes haemolysis, platelet activation, and degradation of High Molecular Weight von Willebrand Factor (HMW vWF) multimers, all of which are dependent on the exposure time and magnitude of shear stress. Specifically, accumulating evidence supports that when blood is exposed to shear stresses above a certain threshold, blood trauma ensues; however, it remains unclear how various constituents of blood are affected by discrete shears experimentally. The aim of this study was to expose blood to discrete shear stresses and evaluate blood trauma indices that reflect red cell, platelet, and vWF structure. Citrated human whole blood (n = 6) was collected and its haematocrit was adjusted to 30 ± 2% by adding either phosphate buffered saline (PBS) or polyvinylpyrrolidone (PVP). Viscosity of whole blood was adjusted to 3.0, 12.5, 22.5 and 37.5 mPa·s to yield stresses of 3, 6, 9, 12, 50, 90 and 150 Pa in a custom-developed shearing system. Blood samples were exposed to shear for 0, 300, 600 and 900 s. Haemolysis was measured using spectrophotometry, platelet activation using flow cytometry, and HMW vWF multimer degradation was quantified with gel electrophoresis and immunoblotting. For tolerance to 300, 600 and 900 s of exposure time, the critical threshold of haemolysis was reached after blood was exposed to 90 Pa for 600 s (P < 0.05), platelet activation and HMW vWF multimer degradation were 50 Pa for 600 s and 12 Pa for 300 s respectively (P < 0.05). Our experimental results provide simultaneous comparison of blood trauma indices and thus also the relation between shear duration and magnitude required to induce damage to red cells, platelets, and vWF. Our results also demonstrate that near-physiological shear stress (<12 Pa) is needed in order to completely avoid any form of blood trauma. Therefore, there is an urgent need to design low shear-flow medical devices in order to avoid blood trauma in this blood-contacting medical device field. [ABSTRACT FROM AUTHOR]

Abstract: A simple technique to estimate the wall shear rate in healthy arteries using a clinical ultrasound scanner has been developed. This method uses the theory of fully developed oscillatory flow together with a spectral Doppler trace and an estimate of mean arterial diameter. A method using color flow imaging was compared with the spectral Doppler method in vascular phantoms and found to have errors that were on average 35% greater. Differences from the theoretic value for the time averaged wall shear rate using the spectral Doppler method varied by artery: brachial −9 (1) %; carotid −7 (1) %; femoral −22 (4) %; and fetal aorta −17 (10) %. Test measurements obtained from one healthy volunteer demonstrated the feasibility of the technique in vivo. E-mail: (james.blake@ed.ac.uk) [Copyright &y& Elsevier]