Changes In Hydrostatic Pressure Research Articles

Occludin Independently Regulates Permeability under Hydrostatic Pressure and Cell Division in Retinal Pigment Epithelial Cells

The aim of this study was to determine the function of the tight junction protein occludin in the control of permeability, under diffusive and hydrostatic pressures, and its contribution to the control of cell division in retinal pigment epithelium. Occludin expression was inhibited in the human retinal pigment epithelial cell line ARPE-19 by siRNA. Depletion of occludin was confirmed by Western blot, confocal microscopy, and RT-PCR. Paracellular permeability of cell monolayers to fluorescently labeled 70 kDa dextran, 10 kDa dextran, and 467 Da tetramethylrhodamine (TAMRA) was examined under diffusive conditions or after the application of 10 cm H2O transmural pressure. Cell division rates were determined by tritiated thymidine incorporation and Ki67 immunoreactivity. Cell cycle inhibitors were used to determine whether changes in cell division affected permeability. Occludin depletion increased diffusive paracellular permeability to 467 Da TAMRA by 15%, and permeability under hydrostatic pressure was increased 50% compared with control. Conversely, depletion of occludin protein with siRNA did not alter diffusive permeability to 70 kDa and 10 kDa RITC-dextran, and permeability to 70 kDa dextran was twofold lower in occludin-depleted cells under hydrostatic pressure conditions. Occludin depletion also increased thymidine incorporation by 90% and Ki67-positive cells by 50%. Finally, cell cycle inhibitors did not alter the effect of occludin siRNA on paracellular permeability. The data suggest that occludin regulates tight junction permeability in response to changes in hydrostatic pressure. Furthermore, these data suggest that occludin also contributes to the control of cell division, demonstrating a novel function for this tight junction protein.

Altered regulation of renal interstitial hydrostatic pressure and the renal renin–angiotensin system in the absence of atrial natriuretic peptide

Although it has been well established that atrial natriuretic peptide gene-disrupted (ANP-/-) mice are a useful model of salt-sensitive hypertension, surprisingly little is known about the control of their intrarenal renin-angiotensin system (RAS) and pressure-natriuresis mechanism, key components in blood pressure, fluid and electrolyte regulation. The aim of this study was to determine whether ANP disruption results in changes in the renal and adrenal local RAS and the acute pressure-natriuresis mechanism. Renal and adrenal renin, angiotensin type 1 (AT1)(A and B) and angiotensin type 2 (AT2) receptor messenger RNA expression levels were determined by northern blotting or real time reverse transcriptase-polymerase chain reaction. Plasma aldosterone and renal and adrenal angiotensin II peptide levels were determined by radioimmunoassay. To examine the acute pressure-natriuresis response, changes in renal interstitial hydrostatic pressure (RIHP) were assessed after manipulations of renal arterial pressure (RAP) in anaesthetized mice. Renal and adrenal renin mRNA and angiotensin II levels were lower in ANP-/- and +/- mice compared with +/+mice. ANP-/- mice also had greater renal AT1A and adrenal AT2 mRNA levels compared with the other genotypes. RAP and RIHP were significantly higher in -/-mice compared with +/+mice. Furthermore, there was a blunted slope of the RAP-RIHP relationship after increases in RAP in ANP-/- mice. These data indicate that ANP disruption results in a blunting of the dynamic properties of the acute pressure-natriuresis mechanism at increased levels of RAP, as well as a reduced expression of renal and adrenal local RAS.

The Uroepithelial-associated sensory web

An important, but not well understood, function of epithelial cells is their ability to sense changes in their extracellular environment and then communicate these changes to the underlying nervous, connective, and muscular tissues. This communication is likely to be important for tube- and sac-shaped organs such as blood vessels, the lungs, the gut, and the bladder, whose normal function can be modulated by stimuli initiated within the epithelium. We propose that the uroepithelium, which lines the renal pelvis, ureters, and inner surface of the bladder, functions as an integral part of a 'sensory web.' Through uroepithelial-associated channels and receptors, the uroepithelium receives sensory 'inputs' such as changes in hydrostatic pressure and binding of mediators including adenosine triphosphate (ATP). These input signals stimulate membrane turnover in the outermost umbrella cell layer and release of sensory 'outputs' from the uroepithelium in the form of neurotransmitters and other mediators that communicate changes in the uroepithelial milieu to the underlying tissues, altering their function. The global consequence of this sensory web is the coordinated function of the bladder during the cycles of filling and voiding, and disruption of this web is likely to lead to bladder dysfunction.

Pressure tuning of whispering gallery mode resonators

The effect of hydrostatic pressure on solid and hollow microsphere optical resonators was investigated. The primary goal was to explore the feasibility of a micro-optical pressure sensor based on whispering gallery modes (WGMs) and to quantify the deleterious effect of environmental pressure changes on other WGM-based sensors. Expressions were developed for WGM shifts due to changes in hydrostatic pressure of the environment surrounding the spherical resonators. These expressions were validated through experiments in which the pressure-induced WGM shifts of hollow polymethyl methacrylate microspheres were monitored. The effect of atmospheric pressure variations on silica resonators is negligible, but hydrostatic pressure may be effective in the optical tuning of hollow polymer spheres.

Sea‐level related resedimentation processes on the northern slope of Little Bahama Bank (Middle Pleistocene to Holocene)

AbstractMiddle Pleistocene to Holocene sediment variations observed in a 26 metre long core taken during a cruise of the RV Marion Dufresne are presented. Core MD992202 was retrieved from the northern slope of Little Bahama Bank and provides an excellent example for sedimentation processes in a mid‐slope depositional environment. The sediment composition indicates sea‐level related deposition processes for the past 375 000 years (marine isotope stages 1 to 11). The sediments consist of: (i) periplatform ooze (fine‐grained particles of shallow‐water and pelagic origin) with moderate variations in carbonate content, carbonate mineralogy and grain‐size; and (ii) coarser intervals with cemented debris consisting of massive, poorly sorted, mud‐supported or clast‐supported deposits with an increased high‐magnesium calcite content. During interglacial stages (marine isotope stages 1, 5, 7, 9 and 11) periplatform oozes (i) are characterized by higher aragonite contents, finer grain‐size and higher organic contents, whereas during glacial stages (marine isotope stages 2 to 4, 6, 8 and 10), increased low‐magnesium and high‐magnesium calcite values, coarser grain‐size and lower organic contents are recorded. These glacial to interglacial differences in mineralogy, grain‐size distribution and organic content clearly show the impact of climatically controlled sea‐level fluctuations on the sedimentation patterns of the northern slope of Little Bahama Bank. The coarser deposits (ii) occur mainly at the transitions from glacial to interglacial and interglacial to glacial stages, and are interpreted as redeposition events, indicating a direct link between sediment properties (changes in mineralogy, grain‐size distribution, variations in organic contents) and sea‐level fluctuations. Changes in hydrostatic pressure and the wave base position during sea‐level changes are proposed to have triggered these large‐scale sediment redepositions.

Effect of physical variables on particle critical erosion shear stress: Hydrostatic pressure, slope and changes in water density

In recent years, the importance of organo-mineral aggregates (OMAs) in the transport of organic material from the continental shelf to the deep ocean floor has been recognized. Attempts to model the transport of these OMAs rely on measurements of several physical parameters, such as the critical erosion shear stress. However, due to technical constraints, such measurements are not done in situ, making it difficult to assess the impact of environmental parameters on the measurements made, and their accuracy in representing the study site. Changes in hydrostatic pressure, slope angle and water density potentially can affect the critical erosion shear stress of OMAs. Using new methodologies, we found no measurable effect of hydrostatic pressure variation on the OMAs' resuspension behavior. Changes in slope angle resulted in the decrease of u∗ cri up to 35%. The u∗ cri decreased by 9% with an exchange with denser water, and it increased by 6% with an exchange with lighter water. These changes were temporary, and after a 3-h stabilization the u∗ cri returned to the original value. We will discuss the future applications of these results on modeling of particle transport.

Scanning sports medicine

An Ultracyclist with Pulmonary Edema During the Bicycle Race Across America A recently published case report in the January 2007 issue of Medicine & Science in Sports & Exercise, the official journal of the ACSM, highlights the pitfalls of overly aggressive sodium intake during an endurance race at altitude. It is well known that multiday ultra-endurance athletic events tax the body’s ability to maintain sodium and water homeostasis. Much focus has been placed on the danger associated with excessive water intake without sodium repletion, namely hyponatremia. This case study presents the risk associated with aggressive sodium intake coupled with heavy exertion at a high altitude. The subject presented is an extremely fit 38-year-old male participant in the Bicycle Race Across America who developed severe pulmonary edema while cycling at an altitude of 2380 meters on the fourth day of his race. His daily sodium intake over the course of the race averaged between 1000 and 1100 mEq and his weight on the day of hospitalization was 2.7 kg greater than his prerace weight. The athlete responded appropriately to standard support for pulmonary edema while in the hospital and he made a full recovery. Later, he underwent testing for cardiopulmonary disease or susceptibility to high-altitude pulmonary edema. The results of the entire work-up were negative. The authors hypothesize that the excessive sodium intake led to an expanded extracellular volume, increased hydrostatic pressure, and decreased oncotic pressure. Racing at high altitudes, where a hypoxia-induced rise in pulmonary artery pressures already exists, may have exaggerated the effects of the changes in hydrostatic and oncotic pressures seen with extracellular volume expansion. This, coupled with ambient hypoxia, elevated cardiac output, and reduced renal perfusion associated with sustained highlevel exercise seems to lead to the development of acute pulmonary edema.

Changes in [Pr]p and Ht are determinants of renal interstitial hydrostatic pressure (RIHP) change during saline volume expansion in rats

Changes in [Pr]p and Ht are determinants of renal interstitial hydrostatic pressure (RIHP) change during saline volume expansion in rats

Transplanar water transport tester for fabrics

This paper reports on a novel instrument for measuring the water transport behaviour of fabric or paper materials in the transplanar direction. The instrument is unique in that it can not only measure the initial water absorption of the fabric in the transplanar direction, but also the rate of evaporation from the fabric surface after fully saturated with water, with the temperatures of water controlled at different levels simulating the end use conditions of the fabric. Compared with existing instruments for the water transport behaviour of fabrics or papers, the new instrument has a unique mechanism to control the water level underneath the fabric sample at a constant level (i.e. the water level is not reduced with the water transport into or through the fabric sample); as a result, the measurements are not affected by the changes of hydrostatic water pressure during testing. Repeated tests on various fabric samples showed that the measurements from the instrument are accurate, sensitive and reproducible.

Functional morphology of somatic muscles and anterolateral setae in Filinia novaezealandiae Shiel and Sanoamuang, 1993 (Rotifera)

The freshwater rotifer, Filinia novaezealandiae, is a planktonic species in tropical limnetic ecosystems. Like other species in the genus, F. novaezealandiae has two mobile, anterolateral setae that supposedly facilitate saltation through the water column as a means of escape from predators. However, very little is known about setal structure or the control of setal movement. Here, we use a combination of behavioral observations, scanning and transmission electron microscopy, phalloidin staining of F-actin, conventional fluorescence and confocal laser scanning microscopy, and three-dimensional (3D) analysis software to investigate saltation in F. novaezealandiae and gain insight into the contribution that both setae and muscles play in locomotion. Results from EM reveal that the paired anterolateral setae are smooth, hollow extensions of the syncytial integument and constructed of two layers: a thin internal and thick external lamina. The setal cavity is continuous with the body cavity of the trunk, and the setae articulate with the trunk at a series of flexible folds. A lack of direct muscular supply to the setae indicates that their movement is likely to result from a combination of: (1) contractions of specific muscle sets (e.g., anterior transverse muscle, post coronal ring muscle) that insert on the body wall around the setae; and (2) changes in hydrostatic pressure within the body cavity that accompany coronal withdrawal (via contraction of retractor muscles) and extension. These descriptions, together with behavioral observations, indicate that the primary function of the setae is likely to be predator deterrence and not predator evasion. Likewise, saltation is probably a result of heightened coronal activity that immediately follows cycles of setal abduction/adduction. These insights, together with new descriptions of the muscular system in F. novaezealandiae, may be of utility in understanding the evolution of locomotory mechanisms among rotifers.

Adaptation of the antioxidant defence system in hydrothermal‐vent mussels (Bathymodiolus azoricus) transplanted between two Mid‐Atlantic Ridge sites

AbstractThe vent mussel Bathymodiolus azoricus is the dominant member of the Northern Mid‐Atlantic Ridge (MAR) hydrothermal megafauna, and lives in an environment characterized by temporal and spatial variations in the levels of heavy metals, methane and hydrogen sulphide, substances which are known to increase reactive oxygen species levels in the tissues of exposed organisms. To evaluate the effects of two contrasting hydrothermal environments on the antioxidant defence system of this vent mussel species, a 2‐week transplant experiment was carried out involving mussels collected from the relatively deep (2300 m), and chemical rich, Rainbow vent field. These were transplanted to the shallower (1700 m), and relatively less toxic, Lucky Strike vent field. To achieve this objective, levels of superoxide dismutase, catalase (CAT), total glutathione peroxidase (GPx), selenium‐dependent glutathione peroxidase and lipid peroxidation (LPO) were measured in the gills and mantle tissues of resident and transplant mussels before and after the transplant experiment. With the exception of CAT, the gills of the transplanted mussels had significantly higher antioxidant enzyme activity compared with the basal levels in the donor (Rainbow) and recipient (Lucky Strike) populations; whereas the antioxidant enzyme levels in the mantle tissues of the transplants reflected the baseline levels of activity in the native Lucky Strike mussels after 2 weeks. In contrast, LPO levels were significantly higher in both tissue types in the transplants than in either the source or the recipient populations, which suggested a response to hydrostatic pressure change (note, the transplant animals were brought to the surface for transportation between the two vent fields). The fact that the Rainbow mussels survived the transplant experience indicates that B. azoricus has a very robust constitution, which enables it to cope behaviourally, physiologically and genetically with the extreme conditions found in its naturally contaminated deep‐sea environment.

An Ultracyclist with Pulmonary Edema during the Bicycle Race Across America

Ultraendurance athletic events tax the limits of physiological homeostasis. Maintenance of sodium and water balance is a particularly difficult challenge in such events. We present the case of a 38-yr-old participant in the Bicycle Race Across America who developed severe pulmonary edema while cycling at an altitude of 2380 m on the fourth day of the race. With hospitalization and standard support for pulmonary edema, he made a quick, full recovery. A post-race work-up revealed no evidence of underlying cardiopulmonary disease or susceptibility to high-altitude pulmonary edema. His weight on the day of hospitalization was 2.7 kg greater than his pre-race weight. We hypothesize that his excessive daily sodium intake (23-25 g, or 1000-1100 mEq) during the course of the race likely led to an expanded extracellular volume, increased hydrostatic pressure, and decreased oncotic pressure. These factors, in combination with ambient hypoxia, elevated cardiac output, and reduced renal perfusion expected with sustained, high-level exercise, may have led to the development of acute pulmonary edema. This case highlights the pitfalls of overly aggressive sodium intake in endurance races, particularly when such races are conducted at high altitude, where the hypoxia-induced rise in pulmonary artery pressures may amplify the effects of changes in hydrostatic and oncotic pressure that occur with extracellular volume expansion.

ERK 1/2 activation in enhanced osteogenesis of human mesenchymal stem cells in poly(lactic‐glycolic acid) by cyclic hydrostatic pressure

AbstractThe aim of this study was to identify the signal transduction pathways and mechano‐transducers that play critical roles in the processes induced by changes in cyclic hydrostatic pressure and fluid shear in 3‐dimensional (3D) culture systems. Mesenchymal stem cells were loaded into a polymeric scaffold and divided into three groups according to the stress treatment: static, fluid shear, and hydrostatic pressure with fluid shear. Cells were exposed daily to a hydrostatic pressure of 0.2 MPa for 1 min followed by 14 min rest with fluid flow at 30 rpm. Protein extracts were analyzed by Western blot for extracellular signal‐regulated kinase 1/2 (ERK1/2). The complexes were cultured under the mechanical stimuli for 21 days with or without phospho‐ERK1/2 inhibitor (U0126) and evaluated by RT‐PCR, calcium contents, and immunohistochemistry. Under conditions of mechanical stimulation, the activation of ERK1/2 was sustained or increased with time. U0126 suppressed mechanical stimuli‐induced expression of osteocalcin. In addition, calcium contents and the degrees of osteocalcin and osteopontin staining were decreased by this inhibitor. These results demonstrate that mechanical stimuli, particularly hydrostatic pressure with fluid shear, enhance osteogenesis in 3D culture systems via ERK1/2 activation. © 2006 Wiley Periodicals, Inc. J Biomed Mater Res, 2006

Immune Defense Reduces Respiratory Fitness inCallinectes sapidus,the Atlantic Blue Crab

Crustacean gills function in gas exchange, ion transport, and immune defense against microbial pathogens. Hemocyte aggregates that form in response to microbial pathogens become trapped in the fine vasculature of the gill, leading to the suggestion by others that respiration and ion regulation might by impaired during the course of an immune response. In the present study, injection of the pathogenic bacterium Vibrio campbellii into Callinectes sapidus, the Atlantic blue crab, caused a dramatic decline in oxygen uptake from 4.53 to 2.56 micromol g-1 h-1. This decline in oxygen uptake is associated with a large decrease in postbranchial PO2, from 16.2 (+/-0.46 SEM, n=7) to 13.1 kPa (+/-0.77 SEM, n=9), while prebranchial PO2 remains unchanged. In addition, injection of Vibrio results in the disappearance of a pH change across the gills, an indication of reduced CO2 excretion. The hemolymph hydrostatic pressure change across the gill circulation increases nearly 2-fold in Vibrio-injected crabs compared with a negligible change in pressure across the gill circulation in saline-injected, control crabs. This change, in combination with stability of heart rate and branchial chamber pressure, is indicative of a significant increase in vascular resistance across the gills that is induced by hemocyte nodule formation. A healthy, active blue crab can eliminate most invading bacteria, but the respiratory function of the gills is impaired. Thus, when blue crabs are engaged in the immune response, they are less equipped to engage in oxygen-fueled activities such as predator avoidance, prey capture, and migration. Furthermore, crabs are less fit to invade environments that are hypoxic.

Critical Slip in Maximum Electromagnetic Power of a Motor for Borehole Prospecting Mechatronic Devices

The extraordinary conditions for borehole motors such as: wide operating medium temperature change interval from –20oC up to +250oC, hydrostatic pressure changes from atmospheric up to 210 MPa, operating medium – dielectric liquid, limited power source, long geophysical, cable of up to 10,000 m non-constant load, due to the operating cycle have influence on their reliable operating, maximum power transmission, and change of characteristics. In this particular case, it is important to know the maximum electromagnetic power, which may be created by the motor. The critical slip and maximum electromagnetic power of the induction motor with a solid rotor supplied from a limited power-source and through the complex circuit, taking into account the parameters of the motor and supply circuit, as well as the operating peculiarities, have been derived. The study of computed characteristics of the borehole motor, taking into account the above-mentioned conditions, show that the motor supplied from a limited power-supply source and through the complex circuit should be investigated inseparably from the whole system.

Solutes in Maternal Circulation and Gestational Sac Compartments during Early Human Development

Objectives: The aim of this study was to review previous work reporting the concentration of solutes measured in maternal circulation, extra-embryonic celomic fluid, and amniotic fluid, to gain insights into the mechanism that could lead to compartmentalization of fluid and solutes within the gestational sac prior to the 12th week of pregnancy. Methods: We conducted a Medline and PubMed literature search from January 1990 through March 2004 using the key words amniotic fluid, celomic fluid, coelomic fluid, celocentesis, coelocentesis, amniocentesis, yolk sac and embryonic cavities. We selected those articles describing solutes that had been measured in the same patient in samples obtained prior to 12 weeks’ gestation from maternal circulation, celomic fluid and amniotic fluid. Information extracted from these publications included: gestational age at sampling, number of samples evaluated, mean concentration of the solutes in each of the three fluids and bibliographic citation. Results: We found 73 publications with the key words and selected 13 that met the inclusion criteria. The concentration of 31 solutes reported in each of the three compartments was documented and gradients among compartmental interfaces calculated. Conclusion: This study describes the concentration of solutes measured in maternal circulation, extracelomic fluid and amniotic fluid early in human development. Analysis of calculated gradients across the compartmental interfaces suggests that the shift of fluid may depend on the biophysical properties of the placenta and yolk sac and on graded changes in hydrostatic pressures across compartments.

Strains inside xylem and inner bark of a stem submitted to a change in hydrostatic pressure

Tangential strains were measured with strain gauges at the surface of xylem and inner bark of saplings of Cryptomeria japonica D. Don. and Fagus silvatica L. during a pressurization test. The test consists in submitting the whole sapling to an artificially imposed hydrostatic pressure of increasing magnitude. The elastic response of the stems was found linear both at the surface of xylem and inner bark. A simple geometric model allows to compute radial strains in each tissue from tangential strain data. Inside inner bark, radial strains are much larger than tangential strains, because tangential strains are restrained by the core of wood. The material compliance of each tissue was computed as the ratio between the radial strain and the pressure that caused it. The material compliance of xylem is much lower than that of inner bark, but, as its thickness is much larger, its contribution to the apparent behavior of the stem is not negligible. Computation of material compliances by this pressurization test provides information about the specific behavior of each tissue in response to hydrostatic pressure. This can be used to estimate and interpret the calibration factor linking the water status of the plant to the apparent strain measured at its surface.

An Influence of Operating Medium Temperature Change on Characteristics of Electric Motor for Borehole Investigating Devices

The extraordinary conditions for borehole motors are following: the operating medium temperature changing interval is from –20oC up to +250oC; the hydrostatic pressure changes from atmospheric up to 210 MPa; the operating medium – dielectric liquid; an energy source is of limited power; the length of geophysical cable is up to 10000 m; the load during the operating cycle is non-constant. These conditions have influence on the motor reliable operating, maximum power transmission, changing of characteristics. The critical slip and maximum electromagnetic power of the induction motor with solid ferromagnetic rotor supplied through the long geophysical cable taking into account the parameters of the motor and supply circuit have been derived. The algorithm and program for study of the borehole motor characteristics taking into account the wide temperature change interval of the borehole operating medium and it’s influence to the parameters of motor and geophysical cable while the cable lengths on the ground surface and let down in borehole are different has been developed. Ill.1, bibl. 7 (in English; summaries in Lithuanian, English and Russian).

Pulse transit time changes observed with different limb positions

Pulse transit time (PTT) is a non-invasive measure of arterial compliance. It can be used to assess instantaneous blood pressure (BP) changes in continual cardiovascular measurement such as during overnight respiratory sleep studies. In these studies, periodic changes in limb position can occur randomly. However, little is known about their possible effects on PTT monitored on the various limbs. The objective of this study was to evaluate PTT differences on all four limbs during two positional changes (lowering and raising of a limb). Ten healthy adults (seven male) with a mean age of 27.0 years were recruited in this study. The results showed that the limb that underwent a positional change had significant (p < 0.05) local PTT differences when compared to its nominal baseline value, whereas PTT changes in the other remaining limbs were insignificant (p > 0.05). The mean PTT value measured from a vertically-raised limb increased by 42.7 ms, while it decreased by 28.1 ms with a half-lowered limb. The PTT differences observed during positional change can be contributed to by the complex interactions between hydrostatic pressure changes, autonomic and local autoregulation experienced in these limbs. Hence the findings herein suggest that PTT is able to reflect local circulatory responses despite changes in the position of other limbs. This can be useful in prolonged clinical observations where limb movements are expected.

Marriage of resistance and conduit arteries breeds critical limb ischemia

Atherosclerosis in a major leg artery leads to impaired blood supply, which normally progresses to critical limb ischemia. Atherosclerosis produces substantial alterations of structure and endothelial function in the large conduit arteries. Pressure unloading and ischemia in the distal vasculature bring about alterations in microvascular function. Resistance arteries undergo significant wall thinning and changes in their contractile regulation. Optimization of large artery dimensions by the small arteries through flow-mediated vasodilation is impaired. Angiogenesis is stimulated, which can result in the formation of major collateral feeder vessels in addition to small nutritive blood vessels. However, angiogenesis can also contribute to instability of atherosclerotic plaques, which ultimately leads to further deterioration in blood supply. Surgical bypass grafting to restore blood supply to the distal leg generates a sudden increase of pressure in the weakened resistance vasculature, leading to uncontrolled changes in capillary hydrostatic pressure, extravasation of fluid, and tissue edema. This review aims to highlight the importance of the resistance vasculature in critical limb ischemia and the interdependence of pathophysiological changes in the large conduit and small resistance arteries. The major unresolved question is why the physiological mechanisms that regulate vascular structure and function ultimately break down, leading to circulatory failure within the distal limb.