Biorheology - Volume 49, issue 1

Authors: Kumar, Bipin | Das, Apurba | Alagirusamy, R.

Article Type: Research Article

Abstract: The efficacy of compression therapy using compression bandages is highly dependent on the level of compression applied and the sustenance of the pressure during the course of treatment. This study attempts to predict the pressure profile generated by compression bandages using constitutive equations describing relaxation behavior of viscoelastic materials. It is observed that this pressure profile is highly correlated with the stress relaxation behavior of the bandage. To model the pressure profile, the stress relaxation behavior of compression bandages was studied and modeled using three mechanical models: the Maxwell model, the standard linear solid model and the two-component Maxwell model …with a nonlinear spring. It was observed that the models with more component values explained the experimental relaxation curves better. The parameters used for modelling relaxation behavior were used to describe the pressure profile, which is significantly dependent on the longitudinal stress relaxation behavior of the bandage, using the modified Laplace's law equation. This approach thus helps in evaluating the bandage performance with time during compression therapy as novel wound care management. Show more

Keywords: Viscoelasticity, wound care, modeling, venous ulcers, mechanical models

DOI: 10.3233/BIR-2012-0601

Citation: Biorheology, vol. 49, no. 1, pp. 1-13, 2012

Authors: Hsiu, Hsin | Hsu, Wei-Chen | Hsu, Chia-Liang | Lin, Wei-Chung | Ho, Ming-Hung | Chen, Chao-Tsung | Hu, Hsiao-Feng

Article Type: Research Article

Abstract: Objective: We aimed to elucidate the frequency-specific microcirculatory blood-flow (MBF) effect induced by weak vibration stimulation (VS) in healthy human subjects. Methods: VS was implemented by a rod (connected to a DC motor) hitting a water-filled bag. VS was applied to the left palm at frequencies near to the heart rate (HR) (n=35; Group A) and 50% higher than the HR (n=20; Group B), and laser-Doppler-flowmetry measurements were made on the back of the left hand (Site 1). A control group without applying VS was also used (n=21). Results: The mean MBF (MMBF), pulsatile MBF, and pulse width …at Site 1 only increased significantly in Group A, and the coefficient of variance of the MMBF sequence increased significantly at Site 1 in Groups A and B. Conclusion: These results illustrate the VS-induced changes in the regulatory activities of arteriolar openings, and improvement of the MBF near the VS application site in Group A. The improvement in MBF depended on whether the VS frequency was near to, or higher than the HR. The present findings may be pertinent to amelioration of disease induced by an abnormal MBF. Show more

Keywords: Vibration stimulation, laser Doppler, frequency, microcirculatory blood flow variability

DOI: 10.3233/BIR-2012-0603

Citation: Biorheology, vol. 49, no. 1, pp. 15-25, 2012

Authors: Brinker, Alexander | Friedrich, Christian

Article Type: Research Article

Abstract: In the explosively growing aquaculture industry, the challenge of sustainability includes a requirement to produce more fish than are consumed by stock. A promising avenue of research is the substitution of the fish meal in feeds with plant protein. However, there are inherent risks in the development of such feeds, and serious consideration should be given not only to nutritional content, but also to the mechanical quality of resulting faecal wastes. The present study uses a plate on plate rheometer running in different flow modes (creep, oscillation) to assess the rheological properties of wastes resulting from different diets. All …faeces were shown to be thixotropic in nature, independent of diet composition. Details of dietary composition influence the consistency and the characteristic stresses at which faecal structure changes from a viscoelastic solid into a viscoelastic liquid. Furthermore, in linking active food components with mechanical properties of chyme faeces, rheological studies may be used to understand and counteract some problematic properties. Substituting 100% of fish meal with plant proteins leads to faeces that rapidly disintegrate into very fine solids which threaten the viability of aquacultural operations. Adding just 0.3% of the rapidly hydrating non-starch polysaccharide, guar gum (GG), significantly increased the viscosity and elastic modulus of the faeces. These mechanical improvements increase the size of the resulting particles and the effectiveness with which they can be removed, thereby leading to optimized water quality. GG addition was sufficiently effective to counter the stability and particle size effects of a 50% substitution of fish meal, but could not mitigate those of a 100% substitution, wherein dissolution effects of an unknown emulsifier are suspected. Show more

Keywords: Effluent treatment, binder, environment, rheology, faeces, sustainability, shear resistance

DOI: 10.3233/BIR-2012-0605

Citation: Biorheology, vol. 49, no. 1, pp. 27-48, 2012

Authors: Zanetti, Elisabetta M. | Perrini, Michela | Bignardi, Cristina | Audenino, Alberto L.

Article Type: Research Article

Abstract: The fundamental passive mechanical properties of the bladder need to be known in order to design the most appropriate long-term surgical repair procedures and develop materials for bladder reconstruction. This study has focused on the bladder tissue viscoelastic behavior, providing a comprehensive analysis of the effects of fibers orientation, strain rate and loading history. Whole bladders harvested from one year old fat pigs (160 kg approximate weight) were dissected along the apex-to-base direction and samples were isolated from the lateral region of the wall, as well as along apex-to-base and transverse directions. Uniaxial monotonic (stress relaxation) and cyclic tests at …different frequencies have been performed with the Bose Electroforce® 3200. Normalized stress relaxation functions have been interpolated using a second-order exponential series and loading and unloading stress–strain curves have been interpolated with a non-linear elastic model. The passive mechanical behavior of bladder tissue was shown to be heavily influenced by frequency and loading history, both in monotonic and cyclic tests. The anisotropy of the tissue was evident in monotonic and in cyclic tests as well, especially in tests performed on an exercised tissue and at high frequencies. In contrast, transverse and apex-to-base samples demonstrated an analogous relaxation behavior. Show more

Keywords: Dynamic, viscoelastic, stiffness, damping, relaxation, cycle number

DOI: 10.3233/BIR-2012-0604

Citation: Biorheology, vol. 49, no. 1, pp. 49-63, 2012

Authors: Kritharis, Eleftherios P. | Giagini, Athina T. | Kakisis, John D. | Dimitriou, Constantinos A. | Stergiopulos, Nikos | Tsangaris, Sokrates | Sokolis, Dimitrios P.

Article Type: Research Article

Abstract: Numerous studies have provided evidence of diameter adaptation secondary to flow-overload, but with ambiguous findings vis à vis other morphological parameters and information on the biomechanical aspects of arterial adaptation is rather incomplete. We examined the time course of large-artery biomechanical adaptation elicited by long-term flow-overload in a porcine shunt model between the carotid artery and ipsilateral jugular vein. Post-shunting, the proximal artery flow was doubled and retained so until euthanasia (up to three months post-operatively), without pressure change. This hemodynamic stimulus induced lumen diameter enlargement, accommodated by elastin fragmentation and connective tissue accumulation, as witnessed by optical and confocal …microscopy. Heterogeneous mass growth of the adventitia was observed at the expense of the media, associated with declining residual strains and opening angle at three months. The in vitro elastic properties of shunted arteries determined by inflation/extension testing were also modified, with the thickness–pressure curves shifted to larger thicknesses and the diameter–pressure curves shifted to larger diameters at physiologic pressures, resulting in normalization of intramural and shear stresses within fifteen and thirty days, respectively. We infer that the biomechanical adaptation in moderate flow-overload leads to normalization of intimal shear, without, however, restoring compliance and distensibility at mean in vivo pressure to control levels. Show more

Keywords: Arteriovenous shunt, remodeling, biomechanical properties, opening angle, elastin, collagen

DOI: 10.3233/BIR-2012-0602

Citation: Biorheology, vol. 49, no. 1, pp. 65-82, 2012