Cinthio, Magnus, Å sa Rydén Ahlgren, Jonas Bergkvist, Tomas Jansson, Hans W. Persson, and Kjell Lindström. Longitudinal movements and resulting shear strain of the arterial wall. Am J Physiol Heart Circ Physiol 291: H394 -H402, 2006. First published February 10, 2006 doi:10.1152/ajpheart.00988.2005.-There has been little interest in the longitudinal movement of the arterial wall. It has been assumed that this movement is negligible compared with the diameter change. Using a new high-resolution noninvasive ultrasonic method, we measured longitudinal movements and diameter change of the common carotid artery of 10 healthy humans. During the cardiac cycle, a distinct bidirectional longitudinal movement of the intimamedia complex could be observed in all the subjects. An antegrade longitudinal movement, i.e., in the direction of blood flow, in early systole [0.39 mm (SD 0.26)] was followed by a retrograde longitudinal movement, i.e., in the direction opposite blood flow [Ϫ0.52 mm (SD 0.27)], later in systole and a second antegrade longitudinal movement [0.41 mm (SD 0.33)] in diastole. The corresponding diameter change was 0.65 mm (SD 0.19). The adventitial region showed the same basic pattern of longitudinal movement; however, the magnitude of the movements was smaller than that of the intimamedia complex, thereby introducing shear strain and, thus, shear stress within the wall [maximum shear strain between the intima-media complex and the adventitial region was 0.36 rad (SD 0.26). These phenomena have not previously been described. Measurements were also performed on the abdominal aorta (n ϭ 3) and brachial (n ϭ 3) and popliteal (n ϭ 3) arteries. Our new information seems to be of fundamental importance for further study and evaluation of vascular biology and hemodynamics and, thus, for study of atherosclerosis and vascular diseases. carotid artery; vascular mechanics; arterial wall movements; shearing strain in arteries; vascular ultrasound IN CARDIOVASCULAR RESEARCH, radial movement of the arterial wall, i.e., diameter change, has been the subject of extensive research. Measurement of radial movements of arteries is an established tool in cardiovascular research (8,13,17,23), forming the basis for estimation of arterial wall stiffness. Increased stiffness of large central arteries has recently been shown to be an independent risk factor for cardiovascular mortality (4). In contrast to radial movements, there has been little interest in longitudinal movements of the arterial wall, i.e., along the vessel. It has been assumed that the longitudinal movement of the arterial wall during the cardiac cycle is negligible compared with the radial movement (21). Longitudinal movement of the arterial wall has not been studied, because, until the most recent improvements in ultrasound systems, it has not been possible to detect longitudinal movement in vivo. In the 1950s, using cinematographic observations of beads sutured to the surface of exposed vessels, Lawton and Greene (15) measured the longitudinal movement of the abd...
A recently introduced silicon microextraction chip (SMEC), used for on-line proteomic sample preparation, has proved to facilitate the process of protein identification by sample clean up and enrichment of peptides. It is demonstrated that a novel grid-SMEC design improves the operating characteristics for solid-phase microextraction, by reducing dispersion effects and thereby improving the sample preparation conditions. The structures investigated in this paper are treated both numerically and experimentally. The numerical approach is based on finite element analysis of the microfluidic flow in the microchip. The analysis is accomplished by use of the computational fluid dynamics-module FLOTRAN in the ANSYS software package. The modeling and analysis of the previously reported weir-SMEC design indicates some severe drawbacks, that can be reduced by changing the microextraction chip geometry to the grid-SMEC design. The overall analytical performance was thereby improved and also verified by experimental work. Matrix-assisted laser desorption/ionization mass spectra of model peptides extracted from both the weir-SMEC and the new grid-SMEC support the numerical analysis results. Further use of numerical modeling and analysis of the SMEC structures is also discussed and suggested in this work.
In this paper, the further development of a silicon flowthrough microdispenser is described. Previously reported designs of the dispenser used bimorph, and later multilayered, piezoelectric actuator elements for the generation of droplets. The introduction of a multilayered actuator significantly reduced the voltage amplitude needed to dispense droplets. Dispenser properties relevant for chemical analysis systems, e.g., reduced sample volume, internal surface area, and dispersion, were improved by miniaturization of the device. In this paper, a new actuator design, the tripod, is presented to enable further dispenser miniaturization and to facilitate device assembly. Tripod actuators were manufactured using a prototyping process, based on micromilling, for multilayer piezoceramic components. A building technique for miniaturized electrical interconnects, based on microstructured flexible printed circuits, is also suggested in line with the prospect of future miniaturization. The microfluidic properties of the tripod-actuated dispenser were evaluated. Stable droplet generation in the frequency range from 0 to 3 kHz was demonstrated, providing a maximum dispensed flow rate of 7.8 L min.[1210]
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