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The effect of pulse pressure on arterial wall remodeling has not been clearly defined. The objective of this study was to evaluate matrix remodeling in arteries under nonpulsatile and hyperpulsatile pressure as compared with arteries under normal pulsatile pressure. Porcine carotid arteries were cultured for 3 and 7 days under normal, nonpulsatile, and hyperpulsatile pressures with the same mean pressure and flow rate using an ex vivo organ culture model. Fenestrae in the internal elastic lamina, collagen, fibronectin, and gap junction protein connexin 43 were examined in these arteries using con focal microscopy, immunoblotting, and immunohistochemistry. Our results showed that after 7 clays, the mean fenestrae size and the area fraction of fenestrae decreased significantly in nonpulsatile arteries (51% and 45%, respectively) and hyperpulsatile arteries (45% and 54%, respectively) when compared with normal pulsatile arteries. Fibronectin decreased (29.9%) in nonpulsatile arteries after 3 days but showed no change after 7 days, while collagen 1 levels increased significantly (106%) in hyperpulsatile arteries after 7 days. The expression of connexin 43 increased by 35.3% in hyperpulsatile arteries after 7 days but showed no difference in nonpulsatile arteries. In conclusion, our results demonstrated, for the first time, that an increase or a decrease in pulse pressure from its normal physiologic level stimulates structural changes in the arterial wall matrix. However, hyperpulsatile pressure has a more pronounced effect than the diminished pulse pressure. This effect helps to explain the correlation between increasing wall stiffness and increasing pulse pressure in vivo. [DOI: 10.1115/1.3202785] Keywords: pulsatile pressure, internal elastic lamina, collagen, fibronectin, connexin 43, porcine artery, ex vivo, organ culture

ABSTRACT. Provided through the screen of a monitor, the participant's resultant center of pressure ([CP.sub.Res]) movements from a force platform device, modified the postural performance of a healthy individual. However, [...]

The effect of pressure upon hydrogen bonding in synthetic end-member clinochlore, ([Mg.sub.5]Al)([Si.sub.3]Al)[O.sub.10][(OH).sub.8], has been studied in situ by high-pressure micro-Raman spectroscopy in a moissanite-anvil cell to 26.5 GPa at 300 K. The ambient spectrum consists of three OH-stretching bands between 3400 and 3650 [cm.sup.-1], attributed to the hydrogen-bonded interlayer OH, and a narrow band at 3679 [cm.sup.-1] that is assigned to the non-hydrogen-bonded OH groups of the talc-like 2:1 layer. The pressure dependence of the OH modes is linear up to 6 GPa. Near 9 GPa a major discontinuity occurs in the pressure dependence of the interlayer OH-stretching modes. It involves frequency increases >100 [cm.sup.-1] that indicate major changes in hydrogen bonding. The OH mode of the 2:1 layer does not show discontinuous behavior at 9 GPa. A further discontinuity occurs at ~16 GPa. This discontinuity affects both interlayer and 2:1 OH, and is likely to be associated with a change in the overall compression mechanism of clinochlore. The spectroscopic behavior is a completely reversible function of pressure. Predictions based upon recent high-pressure diffraction studies of hydrogen bonding and compression of clinochlore suggest that the 9 GPa transition is associated with attainment of an [O.sup.2-]-[O.sup.2] -contact distance of 2.7 [Angstrom].

Metabasites in the high-pressure unit of the southern Dabie Shan (eastern China) contain quartz veins with high-pressure mineral assemblages. Two veins with the parageneses quartz-paragonite-ankerite-rutile and quartz-kyanite-talc-zoisite-rutile-calcite (pseudomorph after aragonite) as well as quartz-kyanite-paragonite-garnet-omphacite were investigated in detail. Host rocks of these veins are garnet amphibolites with eclogitic relics and quartz eclogites, respectively. The oldest phase of deformation (D1) is recorded in the eclogite, which displays a schistosity with shape alignment of high-pressure minerals such as omphacite, phengite and garnet. An estimate of the metamorphic P-T conditions yields 9-21 kbar at 570-620 [degrees]C for the eclogites. Fluid inclusion studies reveal a primary, low-salinity aqueous fluid phase responsible for the formation of the quartz veins. This is in correspondence with calculations of phase equilibrium curves on minerals of the vein paragenesis, which yield P-T conditions of 19.4 kbar and 591 [degrees]C in the presence of an aqueous fluid phase. Geochronology using the U-Pb system of rutile gives evidence for a Triassic minimum age of 207-221 Ma for the vein formation, which fits in the geotectonic framework of the orogen. This rather wide age range arises from the heterogeneous nature of the initial lead isotopic composition, reflecting the heterogeneous sources of the lead and the fluid phase. Part of the fluid was probably generated by prograde dehydration reactions in the country rocks of the veins, whereas strong evidence is also given for the derivation from an older basement, which also underwent subduction. The veins may have formed by extensive hydraulic fracturing or by volume reduction during eclogitisation of the crust. Subsequent to the formation of the veins, great parts of the high-pressure rocks experienced an intensive, syn-tectonic (D2) amphibolite facies metamorphism at 8.5-10.5 kbar and 590-645 [degrees]C, indicating isothermal decompression during exhumation. In the course of this exhumation, pseudosecondary C[O.sub.2] inclusions were trapped in quartz of the veins. The last recorded stage of the retrograde overprint took place under static, greenschist facies conditions (450-480 [degrees]C) in the stability field of kyanite. The shape of the metamorphic P--T path for this stage is reflected by the fluid phase, which either re-equilibrated during this event or penetrated the rock on fractures. These findings show that fluid flow during subduction-related high-pressure metamorphism and subsequent uplift is rather complex; the fluid phase may originate from different sources and may interact with country rocks in the form of a chromatographic column transforming mineral assemblages, and also changing its own character.

High pressure does not cause unfolding of secondary structure units in sperm whale myoglobin but rather smaller conformational changes that provide pathways for water diffusion.

The invention of a high-pressure serial sampler (HPSS) is discussed, focusing on its use to obtain data on oceanic microbial activity. Topics include construction of the HPSS, the relationship between water pressure and microorganisms' metabolic rates, and how the HPSS controls water pressure when obtaining ocean water samples.

A method for evaluating the performance of clinical support surfaces is required by designers in their efforts to produce better clinical support surfaces that will reduce the incidence of pressure ulcers. In this study, a Pressure Index ([P.sub.index]) is defined which is derived from an analytical equation used to evaluate the average interface pressure, the peak pressure, the magnitude of the peak pressure, and the number of peak pressures on the entire body. The type of subjects needed to represent a population of users as well as the head of bed elevations necessary to simulate clinical applications were integrated with the [P.sub.index] to create a single-value mean pressure index which can be used to evaluate any type of surface. To determine the accuracy and repeatability of the mean pressure index, three surfaces (a standard hospital innerspring, a replacement foam mattress, and a low-airloss surface) were tested and evaluated using this method. The low airloss performed the best and the standard innerspring clearly performed the worst (p < 0.0001). The method appeared to accurately and reproducibly predict the relative performance of the three surfaces in reducing pressure. Keywords: pressure ulcer; decubitus ulcer; interface pressure.

The impact of high pressure on Lactobacillus plantarum growth at pH 5.0 and 7.0 was examined. The classical inactivation kinetics were compared with a number of events related to the acid-base physiology of the cell. Findings showed that cells grown at pH 5.0 were more resistant to pressures than cells grown in pH 7.0. After pressure treatment, adenosine triphosphatase (ATPase) activity decreased and acid efflux was impaired. No morphological changes of the membrane were observed although functions related to the membrane-bound ATPase activity were impaired.

A study of the effects of pressure and adenylylation state on dodecamer stacking in the supramolecular self-assembly of Escherichia coli glutamine synthetase suggests that the bimolecular rate constant of the adenylylated enzyme is lower than that of the unadenylylated enzyme. Both enzymes have identical activation enthalpies, indicating that entropic factors contribute to the differences in stacking rates. Stacking in both the enzymes is suppressed by hydrostatic pressure. Adenylylation improves the rate constants for the forward and reverse reactions.

This study investigated the effect of circumferential pressure on timing and muscle-response parameters during ballistic ankle plantar flexion in 15 young healthy subjects. Circumferential pressure was provided by an air-splint applied around the lower calf. Data were collected at 1, 3, and 5 min. prior to, during, and following application of pressure. A 3 X 3 repeated-measures analysis of variance indicated significant increases in premotor and reaction times during application of pressure. There was no main effect for magnitude of muscle activity or motor time. Results support previous studies showing decreases in the excitability of the motor-neuron pool with circumferential pressure and an inverse relationship between excitability and premotor time.

Results reveal that the homotrimeric vesicular stomatitis virus G protein undergoes pressure-induced conformational change that preserves the fusion properties of the virus as seen in an increase in light scattering. This represents a 'fusion-intermediate state' and contain minor changes in secondary structure.

Hines, Tina. Baroreceptor afferent discharge in the pregnant rat. Am J Physiol Regulatory Integrative Comp Physiol 278: R1433-R1440, 2000.--Pregnancy is associated with blunted reflex responses to cardiac and arterial baroreceptor stimulation. We tested the hypothesis that arterial baroreceptor afferent discharge is attenuated in response to a pressure stimulus in pregnant rats. Multifiber aortic depressor nerve activity (ADNA), mean arterial pressure (MAP), and heart rate were measured in anesthetized (pentobarbital sodium, 35 mg/kg ip) late-pregnant and virgin rats in response to increases [phenylephrine (PE), 1.5-24 [micro]g [multiplied by] [kg.sup.-1] [multiplied by] [min.sup.-1] and 1-16 [micro]g/kg] and decreases [sodium nitroprusside (SNP), 5-80 [micro]g [multiplied by] [kg.sup.-1] [multiplied by] [min.sup.-1] and 0.05-16 [micro]g/kg] in MAP. Resting MAP was lower in pregnant rats, but changes in MAP were similar to those in virgin rats during both PE and SNP administration. ADNA was significantly attenuated in pregnant animals during both PE and SNP infusions (P [is less than] 0.05) due to a more rapid adaptation to the pressure stimulus. Bolus drug administration evoked similar changes in MAP and ADNA in both groups; however, the maximum decrease in ADNA was achieved at the lowest dose of SNP in pregnant rats. Thus baroreceptor afferent discharge is attenuated in pregnant rats, and this involves a more rapid adaptation to a pressure stimulus. baroreflex; aortic depressor nerve; phenylephrine; nitroprusside

External pneumatic compression of the lower legs is effective as prophylaxis against deep vein thrombosis. In a typical application, inflatable cuffs are wrapped around the patient' s legs and periodically inflated to prevent stasis, accelerate venous blood flow, and enhance fibrinolysis. The purpose of this study was to examine the stress distribution within the tissues, and the corresponding venous blood flow and intravascular shear stress with different external compression modalities. A two-dimensional finite element analysis (FEA) was used to determine venous collapse as a function of internal (venous) pressure and the magnitude and spatial distribution of external (surface) pressure. Using the one-dimensional equations governing flow in a collapsible tube and the relations for venous collapse from the FEA, blood flow resulting from external compression was simulated. Tests were conducted to compare circumferentially symmetric (C) and asymmetric (A) compression and to examine distributions of pressure along the limb. Results show that A compression produces greater vessel collapse and generates larger blood flow velocities and shear stresses than C compression. The differences between axially uniform and graded-sequential compression are less marked than previously round, with uniform compression providing slightly greater peak flow velocities and shear stresses. The major advantage of graded-sequential compression is found at midcalf. Strains at the lumenal border are approximately 20 percent at an external pressure of 50 mmHg (6650 Pa) with all compression modalities.

Bacteria withstand stress far more gracefully than the rest of us. Sizzle them to above 110 ° C, freeze them to below -10 °, douse them with salt or acid--and, [...]