Analytical and experimental characterization of a miniature calorimetric sensor in pulsatile flow

The behaviour of a miniature calorimetric sensor, which is under consideration for catheter-based coronary artery flow assessment, is investigated in both steady and pulsatile tube flow. The sensor is composed of a heating element operated at constant power, and two thermopiles that measure flow-induced temperature differences over the sensor surface. An analytical sensor model is developed, which includes axial heat conduction in the fluid and a simple representation of the solid wall, assuming a quasi-steady sensor response to the pulsatile flow. To reduce the mathematical problem, described by a two-dimensional advection-diffusion equation, a spectral method is applied. A Fourier transform is then used to solve the resulting set of ordinary differential equations and an analytical expression for the fluid temperature is found. To validate the analytical model, experiments with the sensor mounted in a tube have been performed in steady and pulsatile water flow with various amplitudes and Strouhal numbers. Experimental results are generally in good agreement with theory and show a quasi-steady sensor response in the coronary flow regime. The model can therefore be used to optimize the sensor design for coronary flow assessment

Experimental investigation of collagen waviness and orientation in the arterial adventitia using confocal laser scanning microscopy

Mechanical properties of the adventitia are largely determined by the organization of collagen fibers. Measurements on the waviness and orientation of collagen, particularly at the zero-stress state, are necessary to relate the structural organization of collagen to the mechanical response of the adventitia. Using the fluorescence collagen marker CNA38-OG488 and confocal laser scanning microscopy, we imaged collagen fibers in the adventitia of rabbit common carotid arteries ex vivo. The arteries were cut open along their longitudinal axes to get the zero-stress state. We used semi-manual and automatic techniques to measure parameters related to the waviness and orientation of fibers. Our results showed that the straightness parameter (defined as the ratio between the distances of endpoints of a fiber to its length) was distributed with a beta distribution (mean value 0.72, variance 0.028) and did not depend on the mean angle orientation of fibers. Local angular density distributions revealed four axially symmetric families of fibers with mean directions of 0°, 90°, 43° and −43°, with respect to the axial direction of the artery, and corresponding circular standard deviations of 40°, 47°, 37° and 37°. The distribution of local orientations was shifted to the circumferential direction when measured in arteries at the zero-load state (intact), as compared to arteries at the zero-stress state (cut-open). Information on collagen fiber waviness and orientation, such as obtained in this study, could be used to develop structural models of the adventitia, providing better means for analyzing and understanding the mechanical properties of vascular wal

A Second Order Splitting Algorithm For Thermally-Driven

ABSTRACT A splitting technique for solutions of the Navier-Stokes and the energy equations, in Boussinesq approximation, is presented. The equations are first integrated in time using a splitting procedure and then discretized spatially by means of a high-order spectral element method. The whole technique is validated on the flow in a differentially-heated cavity at intermediate and transitional Rayleigh numbers. The results are in a very good agreement with other available numerical solutions

Modelling regulation of vascular tone following muscle contraction: model development, validation and global sensitivity analysis

In this study the regulation of vascular tone inducing the blood flow increase at the onset of exercise is examined. Therefore, our calf circulation model was extended with a regulation model to simulate changes in vascular tone depending on myogenic, metabolic and baroreflex regulation. The simulated blood flow corresponded to the in vivo response and it was concluded that metabolic activation caused the flow increase shortly after muscle contraction. Secondly, the change in baseline flow upon tilt was a result of myogenic and baroreflex activation. Based on a sensitivity analysis the myogenic gain was identified as most important parameter

Effects of exercise modalities on central hemodynamics, arterial stiffness and cardiac function in cardiovascular disease: Systematic review and meta-analysis of randomized controlled trials

National Natural Science Foundation of China (Nos. 61773110, 61374015, and 61202258 to LX)Fundamental Research Funds for the Central Universities (N161904002 to LX, N172008008 to LQ and N171904009 to LX