JOURNAL OF TEXTURE STUDIES, Issue 2 2000
HARALD ROHM
ABSTRACT A ring test with six participating laboratories and rubber stoppers as reference material was performed to monitor the performance of commercial compression testing instruments. Testing conditions were chosen to be in the range of regular compression testing. Small, single screw instruments with a cantilever exhibited a significant deviation in the force/deformation-response compared with double-screw instruments with a crosshead. Additional tests made with an external device for displacement recording revealed that these differences have to be attributed to insufficient stiffness and some compliance in the cantilever of the tested single-screw instruments. Some consequences of the test results for experiments on soft, semi-soft and rigid food materials are discussed and an equation is developed to correct for the flexing of the cantilever beam in the single screw machine. [source]

RELATIONSHIP BETWEEN ARTERIAL STIFFNESS AND GLUCOSE METABOLISM IN WOMEN WITH METABOLIC SYNDROME

CLINICAL AND EXPERIMENTAL PHARMACOLOGY AND PHYSIOLOGY, Issue 9 2006
Paul Nestel
SUMMARY 1Cardiovascular risk factors associated with the metabolic syndrome affect vascular functions adversely. The aim of the present study was to assess the relationship between parameters of glucose homeostasis and arterial stiffness in women with characteristics of the metabolic syndrome. 2Twenty post-menopausal women participated in a cross-sectional study in which systemic arterial compliance (SAC) and plasma glucose, lipids and glycosylated haemoglobin (HbA1c) were measured while subjects were maintained on a diet high in fibre, raised in protein and reduced in saturated fat. 3Regression analysis suggested that mean ( SD) fasting glucose of 5.9 ± 1.7 mmol/L, glucose levels 2 h after a 75 g glucose load of 6.8 ± 3.6 mmol/L, systolic blood pressure of 131 ± 12 mmHg and HbA1c of 5.3 ± 1.7% predicted SAC negatively. The following correlations were obtained between SAC and: (i) fasting glucose: R = -0.49, P = 0.028; (ii) 2 h glucose level post-glucose load: R = -0.42, P = 0.064; (iii) HbA1c: R = -0.42, P = 0.056; and (iv) systolic blood pressure: R = -0.55, P = 0.012. 4Relationships between SAC and fasting glucose and systolic blood pressure were significantly independent of each other. There was no evidence of relationships between SAC and any plasma lipid parameter (other than a trend in relation to plasma triglyceride), bodyweight or waist circumference. 5In conclusion, in post-menopausal women with metabolic syndrome, fasting plasma glucose and systolic blood pressure, and possibly HbA1c and the 2 h glucose post-glucose load, predicted increased arterial stiffness. [source]

Echo-Tracking Assessment of Carotid Artery Stiffness in Patients with Aortic Valve Stenosis

ECHOCARDIOGRAPHY, Issue 7 2009
Francesco Antonini-Canterin M.D.
Background: There is little information about mechanical properties of large arteries in patients (pts) with aortic stenosis (AS). Methods: Nineteen patients with AS (aortic valve area: 0.88 ± 0.29 cm2) and 24 control subjects without AS but with a similar distribution of risk factors were recruited. , index, pressure-strain elastic modulus (Ep), arterial compliance (AC), augmentation index (AIx), and local pulse-wave velocity (PWV) were obtained at the level of right common carotid artery (CCA) by a real time echo-tracking system. Time to dominant peak of carotid diameter change waveform, corrected for heart rate (tDPc), and maximum rate of rise of carotid diameter (dD/dt) were measured. Systemic arterial compliance (SAC) was also calculated. Parameters of AS severity (mean gradient, valve area, stroke work loss [SWL]) were determined. Results: tDPc was higher in patients with AS than in controls (7.9 ± 0.6 vs. 6.6 ± 0.7, P < 0.0001) while dD/dt was lower (5.3 ± 3.6 mm/s vs. 7.8 ± 2.8 mm/s, P = 0.01). AIx was significantly higher in AS group (32.5 ± 13.6% vs. 20.6 ± 12.2%, P = 0.005) and had a linear correlation both with tDPc (r = 0.63, P < 0.0001) and with dD/dt (r =,0.38, P = 0.01). There was a significant correlation between carotid AC and SAC (r = 0.49, P = 0.03), but only carotid AC was related to SWL (r = 0.51, P = 0.02), while SAC was not (P = 0.26).Conclusions: AIx was the only parameter of arterial rigidity found to be higher in patients with AS than in controls. Carotid AC showed a significant correlation with SAC and it seemed to be more closely related to AS severity than to SAC. [source]

A Novel Approach to Assess Aortic Stiffness Related to Changes in Aging Using a Two-Dimensional Strain Imaging

ECHOCARDIOGRAPHY, Issue 9 2008
Yoshifumi Oishi M.D.
Background: Recently, it has been demonstrated that aortic stiffness is associated with cardiovascular morbidity and mortality. The objective of the present study was to accurately evaluate the aortic stiffness relative to the changes in aging using two-dimensional (2D) strain imaging in 39 comparatively normal patients (15,85 years). Methods: We obtained short-axis images of the abdominal aorta (Ao) and determined the peak circumferential strain (Ao-S) and strain rate (Ao-SR) and the time from Q-wave of electrocardiogram to peak Ao-S using the 2D strain imaging. The stiffness parameters ,1 and ,2 of the abdominal aorta were measured using M-mode ultrasonography and 2D strain imaging, respectively. Results: The stiffness parameters ,1 and ,2 correlated significantly with age (r=0.51, P < 0.001 and r=0.69, P < 0.0001, respectively), particularly the latter parameter ,2. The peak circumferential Ao-S and Ao-SR correlated strongly with age (r=,0.79, P < 0.0001 and r=,0.87, P < 0.0001, respectively). The stiffness parameter ,1 was significantly greater in the old-aged group (>60 years) than in the young-aged group (<30 years). The peak circumferential Ao-S and Ao-SR were significantly lower in the middle-aged (30,60 years) and old-aged groups than in the young-aged group. Conclusion: The aortic circumferential strain and strain rate measured by 2D strain imaging allow simple and accurate determination of the aortic stiffness. [source]

C-Reactive Protein and Aortic Stiffness in Patients with Idiopathic Dilated Cardiomyopathy

ECHOCARDIOGRAPHY, Issue 1 2007
Feridun Kosar M.D.
Background: Previous studies have shown an association between C-reactive protein (CRP)and arterial stiffness in most cardiovascular diseases. Increased CRP levels and arterial stiffness have been considered independent predictors of cardiovascular mortality in cardiovascular disease and even in the general population. Objective: The aim of this study was to investigate the relationship between CRP, a marker of systemic inflammation and aortic stiffness in patients with idiopathic dilated cardiomyopathy (DCMP). Methods: Serum CRP levels and aortic stiffness parameters were measured in DCMP patients (n= 37) and age- and gender-matched control subjects (n= 30). High-sensitivity CRP levels were determined by an immunonephelometry assay. Aortic strain (AS) and aortic distensibility (AD) were calculated from the aortic diameters measured using M-mode echocardiography and blood pressure obtained by sphygmomanometry. Results: Serum levels of CRP in DCMP patients were higher than in the control subjects (5.47 ± 2.06 mg/L and 2.35 ± 0.47 mg/L, P < 0.001, respectively). AS and AD were significantly decreased in DCMP patients compared to the controls (P < 0.001 and P < 0.001, respectively). There were positive correlations between CRP, and (r = 0.3.64, P = 0.027) smoking (r = 0.3.56, P = 0.024), and increasing age (r = 0.587, P < 0.001), and negative correlations between CRP, and DBP (r =,0.485, P < 0.001), diameter change (DC; r =,0.493, P < 0.001), AS (r =,0.526, P < 0.001), and AD (r =,0.626, P < 0.001). Conclusion: We have shown that there is a significant relation between high serum CRP levels and impaired aortic stiffness in patients with idiopathic DCMP. These findings may indicate an important role of CRP in the pathogenesis of impaired aortic stiffness in idiopathic DCMP. [source]

Strain-Gradient Elasticity for Bridging Continuum and Atomistic Estimates of Stiffness of Binary Lennard-Jones Crystals

ADVANCED ENGINEERING MATERIALS, Issue 6 2010
Andrei A. Gusev
Lagrangian variational approach is employed to derive the equations of equilibrium of strain-gradient elasticity. For a periodic lamellar-morphology strain-gradient medium, we present an exact formula for the overall, system stiffness. We compare the formula with direct atomistic estimates of stiffness of binary Lennard-Jones crystals. The comparison reveals that the strain-gradient formula remains fairly accurate for all the crystals studied, including those with order of unity atoms in the crystal unit cell. Thus, one can surmise that the strain-gradient correction alone can already be sufficient to extend the scope of validity of continuum-level elasticity to near atomistic length scales. [source]

Biodegradable Polymer Crosslinker: Independent Control of Stiffness, Toughness, and Hydrogel Degradation Rate

ADVANCED FUNCTIONAL MATERIALS, Issue 19 2009
Chaenyung Cha
Abstract Hydrogels are being increasingly studied for use in various biomedical applications including drug delivery and tissue engineering. The successful use of a hydrogel in these applications greatly relies on a refined control of the mechanical properties including stiffness, toughness, and the degradation rate. However, it is still challenging to control the hydrogel properties in an independent manner due to the interdependency between hydrogel properties. Here it is hypothesized that a biodegradable polymeric crosslinker would allow for decoupling of the dependency between the properties of various hydrogel materials. This hypothesis is examined using oxidized methacrylic alginate (OMA). The OMA is synthesized by partially oxidizing alginate to generate hydrolytically labile units and conjugating methacrylic groups. It is used to crosslink poly(ethylene glycol) methacrylate and poly(N -hydroxymethyl acrylamide) to form three-dimensional hydrogel systems. OMA significantly improves rigidity and toughness of both hydrogels as compared with a small molecule crosslinker, and also controls the degradation rate of hydrogels depending on the oxidation degree, without altering their initial mechanical properties. The protein-release rate from a hydrogel and subsequent angiogenesis in vivo are thus regulated with the chemical structure of OMA. Overall, the results of this study suggests that the use of OMA as a crosslinker will allow the implantation of a hydrogel in tissue subject to an external mechanical loading with a desired protein-release profile. The OMA synthesized in this study will be, therefore, highly useful to independently control the mechanical properties and degradation rate of a wide array of hydrogels. [source]

Microfluidic Endoskeletons: Materials of Controlled Shape and Stiffness with Photocurable Microfluidic Endoskeleton (Adv. Mater.

ADVANCED MATERIALS, Issue 27 2009
27/2009)
Photocurable microfluidic channel networks in thin layers of polydimethylsiloxane can act as on-demand endoskeletons to lock-in specific shapes, report Orlin Velev and co-workers on p. 2803. The light-induced solidification of photopolymer inside the microchannel networks leads to drastic increases in the elastic and bending moduli of the elastomeric material. The fabrication process is simple and scalable, and could make use of other shape-memory materials, creating the potential to fabricate custom shapes (e.g., containers, protective exoskeletons, or supports) using simple heat, light, or magnetic/electric field triggers. [source]

Materials of Controlled Shape and Stiffness with Photocurable Microfluidic Endoskeleton

ADVANCED MATERIALS, Issue 27 2009
Suk Tai Chang
Photocurable microfluidic channel networks in thin layers of polydimethylsiloxane can act as on-demand endoskeletons to lock-in specific shapes. The light-induced solidification of photopolymer inside the microchannel networks leads to drastic increases in the elastic and bending moduli of the elastomeric material. [source]

Thin Films: One Nanometer Thin Carbon Nanosheets with Tunable Conductivity and Stiffness (Adv. Mater.

ADVANCED MATERIALS, Issue 12 2009
12/2009)
Andrey Turchanin and co-workers report on page 1233 on the fabrication and characterization of atomically thin (,1 nm) carbon films and membranes with tunable conductivity and stiffness, arbitrary size and shape. These carbon nanosheets are produced using self-assembled monolayers of aromatic molecules, which are cross-linked by electrons, detached from the surfaces, and subsequently pyrolized. The technical applicability of these novel materials is demonstrated by incorporating them into a microscopic pressure sensor. The optical microscopy image shows a folded nanosheet transferred onto an oxidized silicon wafer. [source]

One Nanometer Thin Carbon Nanosheets with Tunable Conductivity and Stiffness

ADVANCED MATERIALS, Issue 12 2009
Andrey Turchanin
Atomically thin (,1,nm) carbon films and membranes whose electrical behavior can be tuned from insulating to conducting are fabricated by a novel route. These films present arbitrary size and shape based on molecular self-assembly, electron irradiation, and pyrolysis, and their technical applicability is demonstrated by their incorporation into a microscopic pressure sensor. [source]

Fabrication of Bioinspired Actuated Nanostructures with Arbitrary Geometry and Stiffness

ADVANCED MATERIALS, Issue 4 2009
Boaz Pokroy
Bio-inspired, multifunctional, high-aspect-ratio nanostructured surfaces are fabricated in a variety of materials with controlled geometry and stiffness. A soft-lithography method that allows the one-to-one replication of nanostructures and renders it possible to produce arbitrary nanostructures with cross-sectional shapes, orientations, and 2D lattices that are different from the original master is presented. The actuation of the posts is demonstrated. [source]

A time-stepping method for stiff multibody dynamics with contact and friction,

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 7 2002
Mihai Anitescu
Abstract We define a time-stepping procedure to integrate the equations of motion of stiff multibody dynamics with contact and friction. The friction and non-interpenetration constraints are modelled by complementarity equations. Stiffness is accommodated by a technique motivated by a linearly implicit Euler method. We show that the main subproblem, a linear complementarity problem, is consistent for a sufficiently small time step h. In addition, we prove that for the most common type of stiff forces encountered in rigid body dynamics, where a damping or elastic force is applied between two points of the system, the method is well defined for any time step h. We show that the method is stable in the stiff limit, unconditionally with respect to the damping parameters, near the equilibrium points of the springs. The integration step approaches, in the stiff limit, the integration step for a system where the stiff forces have been replaced by corresponding joint constraints. Simulations for one- and two-dimensional examples demonstrate the stable behaviour of the method. Published in 2002 by John Wiley & Sons, Ltd. [source]

Impaired Fasting Glucose Is Associated with Increased Arterial Stiffness in Elderly People without Diabetes Mellitus: The Rotterdam Study

JOURNAL OF AMERICAN GERIATRICS SOCIETY, Issue 3 2006
Nicole M. Van Popele MD
OBJECTIVES: To study the association between impaired fasting glucose (IFG) and arterial stiffness in older adults. DESIGN: Cross-sectional population-based study. SETTING: The Rotterdam Study, a Dutch population-based cohort study. PARTICIPANTS: Two thousand nine hundred eighty-seven subjects aged 60 and older. MEASUREMENTS: Arterial stiffness assessed by measuring common carotid arterial distensibility and glucose status classified into three categories: normal fasting glucose (NFG) (fasting glucose <6.1 mmol/L), IFG (fasting glucose 6.1,6.9 mmol/L), and diabetes mellitus (DM). RESULTS: In the total cohort, common carotid distensibility decreased with increasing impairment of glucose metabolism. Subjects younger than 75 with IFG were comparable with subjects with NFG with respect to arterial stiffness. Subjects aged 75 and older with IFG had stiffer arteries than subjects with NFG, reaching the same arterial stiffness as subjects with DM. For subjects younger than 75, mean difference in distensibility coefficient between subjects with NFG and with IFG was 0.1 (95% confidence interval (CI)=,0.04,0.05, P=.88) and between subjects with NFG and with DM was 1.2 (95% CI=0.7,1.7, P<.001). For subjects aged 75 and older, the mean difference between these groups was 0.7 (95% CI=0.2,1.2, P=.007) and 0.8 (0.3,1.4; P=.002), respectively. In the total cohort, fasting glucose was strongly associated with carotid distensibility (,-coefficient=,0.29, P<.001). CONCLUSION: IFG is related to arterial stiffness in elderly subjects. An advanced stage of arterial stiffness, comparable with that of subjects with DM, is only reached at the age of 75. [source]

Late-Life Depression is Associated with Arterial Stiffness: A Population-Based Study

JOURNAL OF AMERICAN GERIATRICS SOCIETY, Issue 8 2003
Henning Tiemeier MD
Objectives: To determine whether arterial stiffness is associated with depression in the elderly. Design: Population-based cross-sectional study. Setting: In Ommoord, a suburb of Rotterdam, the Netherlands. Participants: Three thousand seven hundred four subjects of the Rotterdam Study aged 60 and older. Measurements: Arterial stiffness was assessed using the distensibility of the carotid artery and the carotid-femoral pulse wave velocity. All participants were screened for depressive symptoms with the Center for Epidemiologic Studies,Depression scale. Those with depressive symptoms had a psychiatric evaluation to establish a diagnosis of depressive disorders according to Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV) criteria. Results: Participants with increased arterial stiffness were more likely to have depressive symptoms. Odds ratios (ORs) for depressive symptoms were 1.24 (95% confidence interval (CI) = 1.01,1.52) per standard deviation decrease in carotid distensibility and 1.17 (95% CI = 1.00,1.38) per standard deviation increase in aortic pulse wave velocity. The association was stronger for depressive disorders meeting DSM-IV criteria (OR = 1.44, 95% CI = 1.03,2.03; OR = 1.48, 95% CI = 1.16,1.90, respectively). Control for atherosclerosis, as measured by the ankle-to-brachial index or presence of plaques in the carotid artery, did not change the associations. Conclusion: This study shows an association between arterial stiffness and depression in the elderly. The findings are compatible with the vascular depression hypothesis. These data suggest that arterial stiffness may partly cause the proposed relationship between vascular factors and depression. [source]

Effect of acute tensile loading on gender-specific tendon structural and mechanical properties

JOURNAL OF ORTHOPAEDIC RESEARCH, Issue 4 2009
Katherine E. Burgess
Abstract Stretching is commonly used prior to exercise, as it is thought to reduce the risk of injury, and it is also used in the preconditioning of tendon grafts. As tendon properties have been shown to be different between genders, it is proposed that stretching will differentially affect the structure. Here we examine the effect of acute stretch on the mechanical properties of both male and female medial gastrocnemius tendon. Female [20 years,±,1 (SEM), n,=,17] and male (22 years,±,1, n,=,18) subjects underwent a 5-min passive dorsiflexion stretch. Prior to and post stretch medial gastrocnemius tendon stiffness (K), length (l) and cross-sectional area (csa) were measured using ultrasonography and dynamometry. Stiffness and Young's modulus (,) were significantly reduced with stretch for both genders (p,<,0.05). Females showed significantly (p,<,0.05) greater pre- to poststretch decreases in K (22.4 vs. 8.8%) and , (20.5 vs. 8.4%) in comparison to males. The present results show that stretching acutely reduces stiffness of the medial gastrocnemius tendon in females and males, with females showing significantly greater change. The observed disparity between genders may be due in part to variations in tendon moment arm and intrinsic differences in tendon composition. These differential changes in tendon mechanical properties have functional, motor control, and injury risk implications, as well as possible implications for preconditioning of tendon grafts. © 2008 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 27: 510,516, 2009 [source]

Effect of freeze-drying and gamma irradiation on the mechanical properties of human cancellous bone

JOURNAL OF ORTHOPAEDIC RESEARCH, Issue 3 2000
O. Cornu
Freeze-drying and gamma irradiation are commonly used for preservation and sterilization in bone banking. The cumulative effects of preparation and sterilization of cancellous graft material have not been adequately studied, despite the clinical importance of graft material in orthopaedic surgery. Taking benefit from the symmetry of the left and right femoral heads, the influence of lipid extraction followed by freeze-drying of a femoral head and a final 25-kGy gamma irradiation was determined, with the nonirradiated, nonprocessed counterpart as the control. Five hundred and fifty-six compression tests were performed (137 pairs for the first treatment and 141 pairs for the second). Mechanical tests were performed after 30 minutes of rehydration in saline solution. Freeze-dried femoral heads that had undergone lipid extraction experienced reductions of 18.9 and 20.2% in ultimate strength and stiffness, respectively. Unexpectedly, the work to failure did not decrease after this treatment. The addition of gamma irradiation resulted in a mean drop of 42.5% in ultimate strength. Stiffness of the processed bone was not modified by the final irradiation, with an insignificant drop of 24%, whereas work to failure was reduced by a mean of 71.8%. Freeze-dried bone was a bit less strong and stiff than its frozen control. Its work to failure was not reduced, due to more deformation in the nonlinear domain, and it was not brittle after 30 minutes of rehydration. Final irradiation of the freeze-dried bone weakened its mechanical resistance, namely by the loss of its capacity to absorb the energy (in a plastic way) and a subsequent greater brittleness. [source]

Stiffness, viscosity, and upper-limb inertia about the glenohumeral abduction axis

JOURNAL OF ORTHOPAEDIC RESEARCH, Issue 1 2000
Li-Qun Zhang
To evaluate the dynamic properties of the shoulder and understand how they are controlled by the central nervous system, glenohumeral-joint stiffness and viscosity and upper-limb inertia were quantified under various levels of muscle contraction in seven healthy human subjects. Through a cast attachment, the upper limb was perturbed in a precise pattern by a computer-controlled servomotor to manifest the dynamic properties of the joint. The recorded joint position and torque were used to estimate joint stiffness and viscosity and upper-limb inertia. With moderate muscle contraction, the stiffness and viscosity increased several fold. A stiffer shoulder joint associated with stronger muscle contraction made the shoulder more stable and protected it from potential injuries during strenuous tasks. Joint viscosity, especially the stronger viscous damping associated with more strenuous contraction, smoothed shoulder movement and stabilized the joint. From the control viewpoint, the glenohumeral joint responded to the central nervous system more quickly with increasing muscle contraction, which was useful during strenuous tasks. On the other hand, the central nervous system controlled stiffness and viscosity synchronously so that it dealt with only a nearly constant damping ratio of the joint over various levels of contraction, which simplified its task substantially. This approach quantified the dynamic and static properties of the shoulder under various levels of contraction more accurately and completely than a manual test, and it can potentially be used to evaluate changes in these properties caused by musculoskeletal injuries and their surgical treatments. [source]

On Toughness and Stiffness of Poly(butylene terephthalate) with Epoxide-Containing Elastomer by Reactive Extrusion

MACROMOLECULAR MATERIALS & ENGINEERING, Issue 8 2004
Zhong-Zhen Yu
Abstract Summary: To obtain a balance between toughness (as measured by notched impact strength) and elastic stiffness of poly(butylene terephthalate) (PBT), a small amount of tetra-functional epoxy monomer was incorporated into PBT/[ethylene/methyl acrylate/glycidyl methacrylate terpolymer (E-MA-GMA)] blends during the reactive extrusion process. The effectiveness of toughening by E-MA-GMA and the effect of the epoxy monomer were investigated. It was found that E-MA-GMA was finely dispersed in PBT matrix, whose toughness was significantly enhanced, but the stiffness decreased linearly, with increasing E-MA-GMA content. Addition of 0.2 phr epoxy monomer was noted to further improve the dispersion of E-MA-GMA particles by increasing the viscosity of the PBT matrix. While use of epoxy monomer had little influence on the notched impact strength of the blends, there was a distinct increase in the elastic stiffness. SEM micrographs of impact-fracture surfaces indicated that extensive matrix shear yielding was the main impact energy dissipation mechanism in both types of blends, with or without epoxy monomer, and containing 20 wt.-% or more elastomer. SEM micrographs of freeze-fractured surfaces of PBT/E-MA-GMA blend illustrating the finer dispersion of E-MA-GMA in the presence of epoxy monomer. [source]

ORIGINAL RESEARCH,ENDOCRINOLOGY: Pulse Pressure, an Index of Arterial Stiffness, Is Associated with Androgen Deficiency and Impaired Penile Blood Flow in Men with ED

THE JOURNAL OF SEXUAL MEDICINE, Issue 1 2009
Giovanni Corona MD
ABSTRACT Introduction., Pulse pressure (PP; i.e., the arithmetic difference between systolic and diastolic blood pressure) reflects arterial stiffness and has been suggested to be an independent cardiovascular risk factor. Aim., The aim of the present study is to asses the possible contribution of PP to arteriogenic erectile dysfunction (ED) and ED-associated hypogonadism. Methods., A consecutive series of 1,093 (mean age 52.1 ± 13.0 years) male patients with ED and without a previous history of hypertension or not taking any antihypertensive drugs were investigated. Main Outcome Measures., Several hormonal and biochemical parameters were studied, along with structured interview on erectile dysfunction (SIEDY), ANDROTEST structured interviews, and penile Doppler ultrasound. Results., Subjects with higher PP quartiles showed worse erectile function and higher prevalence of arteriogenic ED even after adjustment for confounding factors. Furthermore, sex hormone binding globulin-unbound testosterone levels declined as a function of PP quartiles. Accordingly, the prevalence of overt hypogonadism (calculated free testosterone < 180 pmol/L or free testosterone < 37 pmol/L) increased as a function of PP quartiles (17.% vs. 39.7%, and 30.8% vs. 58.6% for the first vs. fourth quartile, respectively, for calculated free testosterone and free testosterone; all P < 0.0001 for trend). This association was confirmed even after adjustment for confounders (Adjusted [Adj]) r = 0.090 and 0.095 for calculated free testosterone < 180 pmol/L and free testosterone < 37 pmol/L, respectively; all P < 0.05). Conclusions., PP is an easy method to estimate and quantify patient arterial stiffness. We demonstrated here for the first time that elevated PP is associated with arteriogenic ED and male hypogonadism. The calculation of PP should became more and more familiar in the clinical practice of health care professionals involved in sexual medicine. Corona G, Mannucci E, Lotti F, Fisher AD, Bandini E, Balercia G, Forti G, and Maggi M. Pulse pressure, an index of arterial stiffness, is associated with androgen deficiency and impaired penile blood flow in men with ED. J Sex Med 2009;6:285,293. [source]

Titelbild: Microscale Control of Stiffness in a Cell-Adhesive Substrate Using Microfluidics-Based Lithography (Angew. Chem.

ANGEWANDTE CHEMIE, Issue 39 2009
39/2009)
Mikrofluidik-Lithographie wird verwendet, um Blockmuster von zelladhäsiven Hydrogelen mit mikroheterogenen Steifigkeiten zu erzeugen, die die von natürlichem Gewebe nachstellen. Die Mikromuster entstehen, wie S.,K. Sia et,al. in der Zuschrift auf S.,7324,ff. beschreiben, indem man PEG-Fibrinogen mit wechselnden Mengen an Polyethylenglycoldiacrylat in eine Mikrofluidikkammer einspeist. Anschließend werden Zellen auf die Mikromuster gesetzt, um ihre Wechselwirkungen mit der extrazellulären Matrix zu studieren. [source]

Microscale Control of Stiffness in a Cell-Adhesive Substrate Using Microfluidics-Based Lithography,

ANGEWANDTE CHEMIE, Issue 39 2009
Kee Cheung
Mikrofluidik-Lithographie wird verwendet, um Blockmuster von zelladhäsiven Hydrogelen mit mikroheterogenen Steifigkeiten zu erzeugen. Die Mikromuster entstehen, indem man PEG-Fibrinogen mit variierenden Mengen an Polyethylenglycoldiacrylat (PEGDA) in die Mikrofluidikkanäle einspeist (siehe Bild). [source]

Association of Serum Pentosidine With Arterial Stiffness in Hemodialysis Patients

ARTIFICIAL ORGANS, Issue 3 2010
YiLun Zhou
Abstract Pentosidine is an advanced glycation end product (AGE). The present study was undertaken to investigate the association of serum pentosidine with carotid distensibility as a measure of arterial stiffness in hemodialysis patients. One hundred and three patients on maintenance hemodialysis were recruited. The distensibility coefficient of the common carotid artery was evaluated by an ultrasonic phase-locked echo-tracking system. Serum pentosidine was measured by competitive enzyme-linked immunosorbent assay. Serum albumin, lipid profile, calcium, phosphorus, intact parathyroid hormone (iPTH), high-sensitivity C-reactive protein (hs-CRP), and oxidized low-density lipoprotein (ox-LDL) levels were also measured. Correlation was determined by linear and multiple stepwise regression analysis. Serum pentosidine level studied in hemodialysis patients was 0.54 ± 0.13 µg/mL. No significant difference in serum pentosidine level was noted between patients with and without diabetes (0.59 ± 0.10 µg/mL vs. 0.53 ± 0.13 µg/mL, P = 0.062) as well as between patients with and without prior cardiovascular disease (CVD) history (0.56 ± 0.14 µg/mL vs. 0.53 ± 0.12 µg/mL, P = 0.206). In multivariate regression analysis, only age (, = 0.363, P < 0.001) and ox-LDL (, = 0.262, P = 0.004) were identified as independent determinants for serum pentosidine. Serum pentosidine was significantly correlated with carotid distensibility (r = ,0.387, P < 0.001), as well as age, ox-LDL, and hs-CRP. After adjustment for age, blood pressure, history of diabetes, prior CVD history, lipid profile, calcium, phosphorus, iPTH, hs-CRP, and ox-LDL, serum pentosidine was still negatively correlated with distensibility (, = ,0.175, P = 0.044). Serum pentosidine was independently associated with carotid distensibility in hemodialysis patients. This finding suggested that the accumulation of AGE might be an important pathway in the development of arterial stiffness in end-stage renal disease. [source]

Functional Electrical Stimulation-Induced Surface Muscle Stiffness Captured by Computer-Controlled Tonometry

ARTIFICIAL ORGANS, Issue 3 2002
Dietmar Rafolt
Abstract: A new tonometric test system to assess surface stiffness over relaxed and activated calf muscles was developed. The mechanical arrangement consists of a skin indentor driven by a torque motor (galvo-drive) that is rigidly connected to an ankle dynamometer. The indentation depth is measured by a displacement transducer. Software routines for cyclic indentation (recording of stiffness curves), static indentation (sensing of twitch responses), and vibration (skin resonance) were implemented. A visual interface is used to capture surface stiffness during target contractions and during controlled relaxation. For functional electrical stimulation (FES) applications, the software includes a pulse train synthesizer to generate arbitrary stimulation test patterns. The system's performance was tested in FES and voluntary contraction procedures. [source]

Scanning Force Microscopy Based Rapid Force Curve Acquisition on Supported Lipid Bilayers: Experiments and Simulations Using Pulsed Force Mode

CHEMPHYSCHEM, Issue 7 2004
Stephanie Krüger Dr.
Abstract In situ pulsed force mode scanning force microscopy (PFM,SFM) images of phase separated solid-supported lipid bilayers are discussed with the help of computer simulations. Simultaneous imaging of material properties and topography in a liquid environment by means of PFM,SFM is severely hampered by hydrodynamic damping of the cantilever. Stiffness and adhesion images of solid-supported membranes consisting of cholesterol, sphingomyelin, and 1,2-dioleyl-phosphatidylcholine obtained in aqueous solution exhibit contrast inversion of adhesion and stiffness images depending on parameters such as driving frequency, amplitude, and trigger setting. Simulations using a simple harmonic oscillator model explain experimental findings and give a deeper insight into the way PFM,SFM experiments have to be performed in order to obtain interpretable results and hence pave the way for reliable material contrast imaging at high speed. [source]

Large Artery Stiffness: Implications For Exercise Capacity And Cardiovascular Risk

CLINICAL AND EXPERIMENTAL PHARMACOLOGY AND PHYSIOLOGY, Issue 3 2002
Bronwyn A Kingwell
SUMMARY 1. Large artery stiffness, or its inverse, compliance, determines pulse pressure, which, in turn, influences myocardial work capacity and coronary perfusion, both of which impact on exercise capacity and cardiovascular risk. 2. In support of a role for arterial properties in exercise performance, aerobically trained athletes (aged 30,59 years) have lower arterial stiffness than their sedentary counterparts. Furthermore, in healthy older subjects (aged 57,80 years), time to exhaustion on treadmill testing correlated positively with arterial compliance. 3. Arterial stiffness is more closely linked to exercise capacity and myocardial risk in patients with coronary disease where, independently of degree of coronary disease, those with stiffer proximal arteries have a lower exercise-induced ischaemic threshold. 4. Moderate aerobic training elevates resting arterial compliance by approximately 30%, independently of mean pressure reduction, in young healthy individuals but not in isolated systolic hypertensive patients. Rat training studies support a role for exercise training in structural remodelling of the large arteries. 5. High-resistance strength training is associated with stiffer large arteries and higher pulse pressure than matched controls. 6. Large artery stiffness is an important modulator of the myocardial blood supply and demand equation, with significant ramifications for athletic performance and ischaemic threshold in coronary disease patients. Moderate aerobic training, but not high-resistance strength training, reduces large artery stiffness in young individuals whereas older subjects with established isolated systolic hypertension are resistant to such adaptation. [source]

Visco-elastic changes of vocal fold mucosa related to high and low relative air humidity

CLINICAL OTOLARYNGOLOGY, Issue 4 2000
R.J.B. Hemler
Objective. To study the effects of high and low relative air humidity (RH) on the visco-elastic properties of the vocal fold cover. Materials and methods. The vocal fold mucosa of sheep larynges was microdissected. The mucosal specimens were attached on one side to an oscillator and on the other side to a force transducer. A sinusoidal oscillation (stress) was applied to the specimen and the transduced force (strain) was recorded in two different conditions of a continuous passing airflow: either dry air (RH = 0%) or humid air (RH = 100%). Of the recorded stress and strain curves the gain and phase-shift between the curves were computed and from these parameters stiffness and viscosity were calculated. In both air conditions the deep surface of the specimen was in contact with a saline bath. Results. Stiffness and viscosity both increased significantly more in dry air than in humid air. This increased stiffness and viscosity returned to baseline values after rehydration. Conclusion. We conclude that these findings indicate that changes in the RH of the airflow passing over the vocal cords influences the visco-elastic properties of the vocal cord cover. [source]

Heel ultrasonography is not a good screening tool for bone loss after kidney and pancreas transplantation

CLINICAL TRANSPLANTATION, Issue 5 2004
Lynn R Mack-Shipman
Abstract:, Background:, Solid organ transplant recipients, particularly simultaneous pancreas kidney recipients, are at high fracture risk. We tested whether quantitative ultrasonography (QUS) of the heel predicts bone mineral density (BMD) by dual energy X-ray absorptiometry (DXA) in solid organ transplant recipients. Methods:, Thirty-eight transplant recipients (22 Female/16 Male) were studied. Spine and hip BMD was measured with a Hologic DXA scanner. ,Stiffness' of the heel was measured with a Lunar Ultrasound densitometer and compared with BMD by DXA. Contributing factors to bone loss were also assessed. Results:, Mean age was 43.1 ± 1.3 yr. Simultaneous pancreas-kidney, kidney, and pancreas alone transplant recipients were assessed. Mean time post-transplantation was 3.0 ± 0.6 yr. Mean DXA spine T-score was ,1.15 ± 0.22 (mean ± SEM) and hip T-score was ,1.22 ± 0.20. There was no difference in mean T-score between women and men at the hip or spine. Mean right heel stiffness T-score was ,0.97 ± 0.25. There was no correlation between QUS and DXA at either the hip or spine in women or men. QUS had a false negative rate for identifying osteopenia or osteoporosis of 17% compared with DXA. The false positive rate for identifying osteopenia was 61%. Conclusions:, The QUS is an unacceptable tool for identifying those at risk for bone loss after kidney or pancreas transplantation. [source]