A Strain Device Imposing Dynamic and Uniform Equi-Biaxial Strain to Cultured Cells

The objective of this study is to design a new apparatus to allow the control of the magnitude and frequency of dynamic stretch applied uniformly to cells cultured on a silicon elastic membrane. The apparatus is designed to produce equi-biaxial dynamic stretches with area changes ranging from 0% to 55% and frequencies ranging from 0 to 2 Hz. Homogeneous finite strain analysis using triangles of markers was performed to compute the symmetric two-dimensional Lagrangian strain tensor on the membrane. Measurements of strain in both static and dynamic conditions showed that the shear component of the strain tensor (E_rc) was near zero, and that there was no significant difference between radial (E_rr) and circumferential (E_cc) components, indicating the attainment of equi-biaxial strain. Bovine aortic endothelial cells were transiently transfected with a chimeric construct in which the luciferase reporter is driven by TPA-responsive elements (TRE). The transfected cells cultured on the membrane were stretched. The luciferase activity increased significantly only when the cells were stretched by 15% or more in area. Cells in different locations of the membrane showed similar induction of luciferase activities, confirming that strain is uniform and equi-biaxial across the membrane. © 1998 Biomedical Engineering Society. PAC98: 8780+s, 8745-k, 8722-q     

A model of electrical activity and cytosolic calcium dynamics in vascular endothelial cells in response to fluid shear stress

A mathematical model is proposed to describe the intracellularCa ²⁺ (Ca _i) transient and electrical activity of vascular endothelial cells (VEC) elicited by fluid shear stress (τ). The intracellularCa ²⁺ store of the model VEC is comprised of aCa _i-sensitive (sc) and an inositol (1,4,5)-trisphosphate (IP ₃)-sensitive compartment (dc). The dc [Ca ²⁺] is refilled by the sc whose [Ca ²⁺] is the same as extracellular [Ca ²⁺].IP ₃ produced by the τ-deformed mechanoreceptors discharges the dcCa ²⁺ into the cytosol. The increase of cytosolic[Ca ²⁺] inducesCa ²⁺ release (CICR) from the sc. The raisedCa _i activates aCa _i-activatedK ⁺ current (I _{K, Ca}) and inhibitsIP ₃ production. The cell membrane potential is determined byI _{K, Ca}, voltage-dependentNa ⁺ andK ⁺ currents. Steady τ>0.1 dyne/cm² elicits aCa _i varies sigmoidally withLog ₁₀(τ) with a maximal peakCa _i of 150 nM at τ=4 dynes/cm². Step increases of τ fail to elicit aCa ²⁺ response in cells previously stimulated by a lower shear. TheCa ²⁺ response gradually decreases with repetitive τ stimuli. Pulsatile shear elicits two to three times higherCa _i and hyperpolarizes the cell more than steady shear of the same magnitude. The simulatedCa ²⁺ responses to τ are quantitatively and qualitatively similar to those observed in cultured VEC. The model provides a possible explanation of why the vasodilating stimulus is greater for pulsatile flow than for nonpulsatile flow.     

Nonhomogeneous Deformation in the Anterior Leaflet of the Mitral Valve

In the mitral valve, regional variations in structure and material properties combine to affect the biomechanics of the entire valve. Previous biaxial testing has shown that mitral valve leaflet tissue is highly extensible, and exhibits nonlinear, anisotropic material properties. In this study, experimental measurements of mitral valve leaflet deformation under quasi-static pressure loading were performed on isolated porcine hearts. Biplane video images of markers placed on the anterior leaflet surface were used to reconstruct the 3D position of the markers at several pressure levels over the physiological range. A least-squares finite-element method was used to fit parametric models to the markers and to calculate the deformation over the surface. The results showed that the leaflet deformations were anisotropic, exhibiting a large nonhomogeneous radial stretch and a small circumferential stretch. This information can be used to better understand how the valve deforms under physiological loading, and to help design treatments for valve problems, such as mitral regurgitation.     

In vitro velocity measurements down strem from the lonescu-Shiley aortic bioprosthesis in steady and pulsatile flow

Velocity measurements were made in vitro using laser Doppler anemometry (LDA) downstream from an lonescu-Shiley (IS) bioprosthetic aortic heart valve. Velocity measurements were made in both steady and pulsatile flow. A systematic, flow mapping approach to the measurement methodology showed that the IS valve generated a large jetlike flow constriction. The acceleration ratio, defined as the maximum mean velocity for the IS valve divided by that for no valve obstructing the flow, was as high as 2·4 for steady flow and 2·6 for pulsatile flow. It was concluded that the IS valve generated a flow quite unlike that observed by other in vestigators for the natural human aortic valve, after which the leaflet design of the IS valve was modelled. In addition, a comparative analysis of steady and pulsatile results was undertaken. It was found that the pulsatile flow results for the systolic ejection interval could be divided into three phases, denoted early, mid, and late systole, as defined by the flow structure at the data plane location. Only during midsystole were the pulsatile flow results approximated by the steady flow results. Also, it was found that the magnitude of the flow disturbance measured in steady flow tended to be an upper bound on that measured for pulsatile flow.     

Evidence for a subgroup of essential hypertensives with non-suppressible excretion of aldosterone during sodium loading

Summary In patients with grade I and II essential hypertension studied during sodium loading (Na⁺ excretion above 175 meq·d^–1) we found a bimodal behaviour of aldosterone excretion and could distinguish two groups of patients: In the major part of essential hypertensives sodium loading led to a suppression of aldosterone excretion below 6 µg·d^–1, which is the highest control value during sodium loading, with an average of 2.7±1.4 (SD) µg·d^–1. Aldosterone excretion in a second group of patients was not suppressible below 6 µg·d^–1 despite forced sodium loading; it resulted in an average value of 10.0±3.0 (SD) µg·d^–1. During sodium deprivation or free sodium intake, aldosterone excretion in the first group of patients followed exactly the behaviour of normotensive controls, while in the second group of essential hypertensives the correlation of aldosterone excretion and log. Na excretion or log. Na⁺/K⁺ ratio in 24 h urine (r=–0.59) was far below the control value ofr=–0.87. Serum potassium concentration during sodium loading was significantly (p<0.001) lower (3.81±0.44 meq·l^–1) in the essential hypertensives with non-suppressible aldosterone excretion compared to those with suppressible aldosterone excretion (4.26±0.37 meq·l^–1). The blood pressure response to treatment with 200 mg spironolactone·d^–1 was better (p<0.05) in patients with non-suppressible aldosterone excretion compared to the essential hypertensives with normal aldosterone regulation. The plasma renin activity of both groups of patients was not significantly different, however, a tendency prevailed towards lower PRA-values in the patient group with non-suppressible aldosterone excretion during sodium loading.With the technical help of Mrs. R. Schendschilorz and Mrs. G. Suckau     

Investigation and improved performance of optical fibre probes in laser Doppler blood flow measurement

Laser Doppler flowmetry with optical-fibre beam transmission is a sensitive fast and convenient method of measuring tissue blood flow. However, its sensitivity can also be a problem because of movement artefacts. This study applies some basic considerations of fibre optics and Rayleigh light scattering to the field of laser Doppler blood flow meters. Practical suggestions are given by which movement arterfacts can be reduced by choice of optical fibres, attention to probe geometry, cladding the fibres to reduce their movements and in the method of application. Experiments which test the normalisation circuitry of laser Doppler instruments are described and the effects of movement artefacts on the interpretation of the pulsatile component of laser Doppler records are also discussed. Probe and fibre line movements cause high-frequency intensity fluctuations due to speckle movement. The intensity fluctuations produce an apparent Doppler shift much greater than the Doppler shift produced by the relative movements of probe and tissue. It has been found that it is important to ensure that the fields of view of the illuminating and detecting fibres do not overlap at the skin surface and that probe contact with the skin surface should be maintained.     

Effects of saline loading on jejunal absorption of calcium,sodium, and water,and on parathyroid hormone secretion in the rat

Summary To investigate whether intestinal calcium absorption parallels that of sodium following extracellular fluid volume expansion, the effects of saline loading on intestinal transport of calcium. sodium and water were studied in rats by perfusing jejunal loops in situ.After calcium-free saline infusion net calcium absorption was reversed similar to that of sodium and water and net secretion occurred. Concurrently, blood-to-lumen (b-l) calcium flux, measured using⁴⁵Ca, increased significantly (P<0.001). Following expansion with calcium-containing Ringer a similar reversal of net calcium, sodium and water flux was also observed. Again, the b-l calcium flux increased but to a significantly lesser extent (P<0.05). Plasma ionized calcium remained unchanged after calcium-rich Ringer loading, but decreased significantly (P<0.001) when calcium was omitted from the solution. Plasma immunoreactive parathyroid hormone was unchanged after expansion with the calcium containing solution but increased following calcium-free infusion.It is concluded that after extracellular fluid volume expansion: 1. net jejunal calcium absorption is decreased; 2. the decrease parallels that of sodium and water; 3. b-l calcium transport is enhanced to a greater degree by calcium-free Ringer infusion than by a calcium-rich solution. This difference could be the result of increased parathyroid hormone secretion.     

Metachromatic leukodystrophy caused by a partial cerebroside sulfatase defect

A patient with neuropathy and myopathy since infancy but whose neuropathy had been stable for a number of years showed a profound deficiency of arylsulfatase A in leukocytes and urine. Urine contained material that stained metachromatically and cochromatographed with cerebroside sulfate. In contrast, cultured fibroblasts contained about 10-20% of normal arylsulfatase A with properties identical to properties of normal fibroblast enzyme, except that it showed no cerebroside sulfatase activity. Growing fibroblasts in the cerebroside sulfate loading test had an attenuated rate of sulfatide hydrolysis. A re-examination of the cerebroside sulfatase reaction revealed that while only limited hydrolysis occurred with low concentrations of taurodeoxycholate or cholate (type I activation), significant hydrolysis of the natural substrate did take place with high concentrations of cholate (type II activation). This suggests that there is a partial cerebroside sulfatase defect in this atypical form of metachromatic leukodystrophy.     

Immediate rehabilitation of a rheumatoid arthritis patient with single-piece implants

Introduction and importanceThe aim of this article is to report the long-term outcome of full mouth rehabilitation with single piece, smooth surface implants following immediate loading protocol on a patient suffering with RA and severe unilateral condylar resorption.Case presentationHere, we present a challenging case of a patient suffering from Rheumatoid Arthritis who was stabilized and completed successfully with a 4 year follow-up period. Prosthetic management optimized the inter-occlusal relationship to maintain both function and esthetic integrity. Single piece implants are designed to engage and take support from the cortical bone low in metabolic activities thus promoting the force transmission through apical threads that are engaged in the cortical bone.DiscussionRheumatoid Arthritis [RA] is an auto-immune inflammatory condition in which the inflamed and hypertrophic synovial membrane grows into the articulation surfaces. The Temporomandibular Joints [TM] are frequently involved in rheumatoid arthritis. According to the literature on RA, due to frequent periodontitis, decreased salivary secretion, medication, as well as decrease in bone regenerative potential, RA is often considered as a relative contraindication in the use of implants. Atrophic jaws and cases with comorbidities like osteoporosis, diabetes, rheumatoid arthritis, periodontally infected cases are restored with high success by single piece smooth surface.ConclusionTo the best of our knowledge, this may be the first case of immediate functional loading by bi-cortical single piece implants.     

一种四点弯曲单向交变应变细胞加载装置的研制

本文根据细胞动力学对力学因素的响应,设计研制了一种四点弯曲单向交变应变加载装置。通过对Wistar大鼠成骨细胞的试验,以及流式细胞仪（FCM）对细胞DNA分析检测的结果,表明研制是成功的,并可广泛使用于内皮细胞、成纤维细胞、平滑肌细胞、心肌细胞等组织工程和生物医学工程、人机工程学、细胞力学方面的研究。