Small Pressure Differences Research Articles

Protective effects of renin–angiotensin blockade beyond blood pressure control

Antihypertensive drugs exert a number of blood pressure-independent benefits. However, demonstrating the clinical significance of these effects may be difficult for a number of reasons. First, blood pressure can be measured in the clinic, at home and over the 24-h period by ambulatory monitoring. Second, differences between these measures mean that achieving equivalent blood pressure reductions in two treatment arms may be difficult, if not impossible. Furthermore, even small differences in blood pressure can translate into significant effects on cardiovascular risk, especially in the later stages of the cardiovascular continuum. In large clinical trials, other errors limiting the sensitivity to treatment differences include high patient dropouts and unplanned crossover. In addition, as so many patients fail to achieve blood pressure goals even in clinical trials where patient's and physician's motivation is high, the need for cardiovascular protection beyond blood pressure control is unequivocal. Clinical trials of angiotensin II receptor blockers have suggested significant effects beyond blood pressure control, which are observed throughout and with greater consistency in the early phases of the cardiovascular continuum. There may also be differences between angiotensin II receptor blockers and angiotensin-converting enzyme inhibitors. Conclusive demonstration that these blood pressure-independent effects do exist will require, however, a much more accurate and extended assessment of the blood pressure effects of the drugs.

A Differential Pressure Instrument with Wireless Telemetry for In-Situ Measurement of Fluid Flow across Sediment-Water Boundaries

An instrument has been built to carry out continuous in-situ measurement of small differences in water pressure, conductivity and temperature, in natural surface water and groundwater systems. A low-cost data telemetry system provides data on shore in real time if desired. The immediate purpose of measurements by this device is to continuously infer fluxes of water across the sediment-water interface in a complex estuarine system; however, direct application to assessment of sediment-water fluxes in rivers, lakes, and other systems is also possible. Key objectives of the design include both low cost, and accuracy of the order of ±0.5 mm H2O in measured head difference between the instrument's two pressure ports. These objectives have been met, although a revision to the design of one component was found to be necessary. Deployments of up to nine months, and wireless range in excess of 300 m have been demonstrated.

Combustion of Ti+0.5C and Ti+C mixtures of bulk density in inert gas coflow

The combustion of Ti-C mixtures of bulk density under inert gas blowing conditions produced by evacuation of one end of the reaction cell was studied for the first time. The experiments showed that the tested mixtures in quartz cups were not ignited and did not burn without the inert gas (argon) flow. Increasing the rate of gas evacuation from the sample increased the rate of steady-state combustion of the mixture of titanium with carbon black, and for the mixture of titanium with graphite, stabilization of the flat combustion front was observed. It is shown that the presence of small pressure difference (up to 105 Pa) allows control of the combustion process and confirms the basic postulates of the convective-conductive theory of combustion for heterogeneous condensed systems.

Wicke–Kallenbach and Graham's diffusion cells: Limits of application for low surface area porous solids

The influence of permeation flux induced by tiny pressure gradients on the counter-current gas diffusion in porous solids is discussed. Binary counter-current gas diffusion in porous samples with a broad range of pore radii (78 nm– 21 μ m ) was studied in arrangements of the Wicke–Kallenbach and Graham's diffusion cells. A small pressure difference between the cell compartments was observed both in the Wicke–Kallenbach cell (7 Pa) and Graham's cell (9 Pa). For samples with pore radii above 7 μ m significant deviations of diffusion fluxes were observed. Limits of pore sizes above which the additional permeation transport influences the diffusion results beyond acceptable level were obtained by simplified calculations. The distorted diffusion fluxes can be numerically freed from the contribution of permeation flux if permeation characteristics are available.

Fast Mass Transport Through Carbon Nanotube Membranes

The May 19, 2006 issue of Science included a paper by Holt et al. on "Fast Mass Transport Through Sub-2-Nanometer Carbon Nanotubes". The paper was also featured on the cover, showing methane molecules translating inside a carbon nanotube (CNT). The authors explained how they prepared 2-6-mum thin membranes consisting of double-walled carbon nanotubes (DWNTs) all aligned perpendicular to the apparent membrane surface. These tubes are open at both ends and the space between the tubes is filled with dense Si(3)N(4). Pure gas and water fluxes were measured at room temperature with the application of a small pressure difference. Interpretation of the results led to the conclusion that the membranes showed much higher fluxes than what was estimated from Knudsen gas diffusion and Poiseuille viscous flow models. The membranes have a straight-channel morphology with a narrow pore-size distribution and exceptionally smooth pore walls. The unusual geometry and surface properties make it difficult to compare the membrane's properties with common membranes but there is no question that the mass transport in the aligned DWNTs is fast indeed. To appreciate how fast, we will consider their transport properties starting from the perspective of "conventional" porous membrane technology. Recent molecular dynamics simulations suggest that none of the classic models for gas (Knudsen) and water (Poiseuille) permeation work in a meaningful way for these nanotube membranes, and new models are needed.

Osmotic Pressure of 3He-4He Solutions at 25.3 Bar and Low Temperatures

The osmotic pressures of dilute 3He-4He solutions were determined at 25.3 bar from measurements of crystallization curves at temperatures from 5 mK to 60 mK, when the 3He component of the solution obeying the Fermi-Dirac statistics was deep in the degenerate state. We determine the shift of the crystallization pressure of the solution of interest relative to pure 4He when both these substances are present in the cell in two separate volumes at the same temperature. We used our novel ultra-sensitive capacitive gauge for measurements of small pressure differences between the two substances. We used a quartz resonator for determination of solution’s concentration in situ. The difference between the crystallization pressure of the saturated solution and pure 4He, both extrapolated to zero temperature, is (339±2) mbar.

BioMEMS: Forging New Collaborations Between Biologists and Engineers

This video describes the fabrication and use of a microfluidic device to culture central nervous system (CNS) neurons. This device is compatible with live-cell optical microscopy (DIC and phase contrast), as well as confocal and two photon microscopy approaches. This method uses precision-molded polymer parts to create miniature multi-compartment cell culture with fluidic isolation. The compartments are made of tiny channels with dimensions that are large enough to culture neurons in well-controlled fluidic microenvironments. Neurons can be cultured for 2-3 weeks within the device, after which they can be fixed and stained for immunocytochemistry. Axonal and somal compartments can be maintained fluidically isolated from each other by using a small hydrostatic pressure difference; this feature can be used to localize soluble insults to one compartment for up to 20 h after each medium change. Fluidic isolation enables collection of pure axonal fraction and biochemical analysis by PCR. The microfluidic device provides a highly adaptable platform for neuroscience research and may find applications in modeling CNS injury and neurodegeneration.

BioMEMS: Forging New Collaborations Between Biologists and Engineers

This video describes the fabrication and use of a microfluidic device to culture central nervous system (CNS) neurons. This device is compatible with live-cell optical microscopy (DIC and phase contrast), as well as confocal and two photon microscopy approaches. This method uses precision-molded polymer parts to create miniature multi-compartment cell culture with fluidic isolation. The compartments are made of tiny channels with dimensions that are large enough to culture neurons in well-controlled fluidic microenvironments. Neurons can be cultured for 2-3 weeks within the device, after which they can be fixed and stained for immunocytochemistry. Axonal and somal compartments can be maintained fluidically isolated from each other by using a small hydrostatic pressure difference; this feature can be used to localize soluble insults to one compartment for up to 20 h after each medium change. Fluidic isolation enables collection of pure axonal fraction and biochemical analysis by PCR. The microfluidic device provides a highly adaptable platform for neuroscience research and may find applications in modeling CNS injury and neurodegeneration.

Fractal design for efficient brittle plates under gentle pressure loading

We consider a plate made from an isotropic but brittle elastic material, which is used to span a rigid aperture, across which a small pressure difference is applied. The problem we address is to find the structure which uses the least amount of material without breaking. Under a simple set of physical approximations and for a certain region of the pressure-brittleness parameter space, we find that a fractal structure in which the plate consists of thicker spars supporting thinner spars in an hierarchical arrangement gives a design of high mechanical efficiency.

The Renin-Angiotensin System in Malignant Hypertension Revisited: Plasma Renin Activity, Microangiopathic Hemolysis, and Renal Failure in Malignant Hypertension

Malignant hypertension is a renin-dependent form of hypertension. However, the variations in renin-angiotensin system (RAS) activation in malignant hypertension are not completely understood. A proposed mechanism for ongoing RAS activation is the presence of microangiopathic hemolysis resulting in renovascular ischemia. We prospectively examined the association between plasma renin activity (PRA), microangiopathic hemolysis, and renal dysfunction in 30 consecutive patients with malignant hypertension (n=18) and severe hypertension (n=12). The PRA and aldosterone were measured in the supine position and before initiating therapy. The PRA was 8.8 ng angiotensin I (AI)/mL/h (interquartile range [IQR] 4.8-20) in malignant hypertensive patients and 2.8 ng AI/mL/h (IQR 0.6-6.3) in patients with severe hypertension (P<.01). Aldosterone was 1.30+/-1.02 nmol/L in patients with malignant hypertension compared with 0.44+/-0.37 nmol/L in those with severe hypertension (P<.01). In malignant hypertension, PRA highly correlated with lactic dehydrogenase (LDH) (r=0.76, P<.001), meaning that 58% of the variations in PRA could be explained by LDH. The PRA positively correlated with serum creatinine values at presentation (r=0.50, P=.007), but adjustment for LDH abolished the effect of PRA on creatinine (P=.24). The PRA and aldosterone were markedly elevated in patients with malignant hypertension but not in severely hypertensive patients despite small differences in blood pressure (BP). The strong logarithmic correlation between PRA, microangiopathic markers, and renal dysfunction suggests a renin-mediated acceleration of vascular damage and renal dysfunction in patients with malignant hypertension.

Socio-economic status and the therapeutic effectiveness of antihypertensive treatment – the design of the LEO study

ABSTRACTObjective: The risk of arterial hypertension and subsequent cardiovascular disease morbidity and mortality increases with low socio-economic status (SES). Even small differences in blood pressure, whether untreated or despite treatment, account for this substantial difference. Most of the increased risk in the low socio-economic group is due to traditional cardiovascular risk factors such as overweight and obesity, alcohol consumption and a sedentary life style. Intense treatment of arterial hypertension has been shown to overcome these prognostic inequalities. Therefore, drugs with high efficacy, optimal treatment adherence and a low potential for drug-related side effects are needed in order to reduce the cardiovascular risk burden of patients with a low SES. The angiotensin receptor blocker (ARB) olmesartan will be used to investigate the effectiveness of this drug in different socio-economic classes.Research design and methods: The LEO (Long-term Effectiveness of Olmesartan in different Socioeconomic groups) study is a large observational long-term study which has been set up to test the effectiveness of olmesartan within this context. The study has a matched-pairs design (1403 patients in both the low and the high socio-economic classes).Main outcome measures: The LEO study will test whether this regimen can reduce the SES-related difference in long-term blood pressure control and compliance in the low SES population.Conclusions: The study may generate valuable information about the antihypertensive effectiveness of olmesartan alone or in combination with hydrochlorothiazide in different socio-economic classes. It will further test whether the drug helps to reduce the inherent inequalities in cardiovascular prognosis between different socio-economic groups.Current status: The study commenced in July 2007. Results are anticipated in December 2008.

Influence of orientation of bi-leaflet valve prostheses on coronary perfusion pressure in humans

Orientation of a bi-leaflet prosthesis (BLP) might influence coronary perfusion. The aim of this study was to investigate the influence of the orientation on coronary perfusion pressure during hyperemia and adrenergic stimulation. During hyperemia perfusion pressure determines coronary blood flow. Fourteen patients with normal coronary angiogram underwent aortic valve replacement (AVR) by a BLP, and seven received a bio-prosthesis. Patients receiving a BLP were randomized to either orientation A (hinge mechanism perpendicular to a line drawn between the coronary ostia) or B (hinge mechanism parallel to the line between the ostia). Six months after surgery all patients underwent cardiac catheterization. Pressures were measured during resting conditions, during maximum hyperemia, and during maximum adrenergic stimulation with a guiding catheter in the aortic arch (P(ao)), simultaneously with a sensor tipped guide wire in the coronary artery (P(cor)) and in the aortic root (P(root)). P(ao)-P(root) described a flow-induced pressure drop in the aortic root (Venturi effect) and the gradient P(root)-P(cor) described coronary ostium abnormalities. Only small non-significant differences in myocardial perfusion pressure were found between different orientations of a bi-leaflet prosthesis or between bi-leaflet prostheses and bio-prostheses in P(ao)-P(root) and P(root)-P(cor).

Microclimate of nesting burrows of the Rainbow Bee-eater

Burrow-nesting affords protection from predators and climatic extremes, but potentially can pose physiological ‘problems’ for developing birds and attendant adults. Microclimate parameters of burrows of breeding Rainbow Bee-eaters (Merops ornatus) were measured to assess whether they presented such difficulties for young and adults. Estimated mean volume of the brood-chamber was ∼4.5 L. Relative humidity was typically 100% in the brood-chamber and chamber air temperature was constant, averaging 4–6°C above ambient levels. The temperature regime of the burrow probably resulted in low thermoregulatory costs for attendant adults and endothermic nestlings. The chamber oxygen (O2) fraction (mean 19.35%) was always lower than ambient values, but mostly not sufficiently low to be problematic for the growing young. Mean pre-internal pipping absolute oxygen consumption rate of embryos (62.9 ± 13.8 mL O2 day−1) did not appear to be strongly influenced by either the protracted incubation period or the reduced O2 partial pressure of the chamber atmosphere. Mean eggshell water-vapour conductance (8.95 mg day−1 kPa−1) was tuned to egg mass rather than egg mass/incubation period. However, eggs still lost ∼15% of their mass during incubation because the influence of the small water-vapour pressure difference across the shell (2.91 kPa) and the protraction of the incubation period apparently counteracted each other.

Fabrication of carbon membrane and microfiltration of oil-in-water emulsion: An investigation on fouling mechanisms

An experimental investigation was carried out on microfiltration of oil-in-water emulsion using the coal-based carbon membrane prepared by carbonization of tubular precursor through extrusion method. Experimental results show that coal is a good precursor for preparation of the carbon membrane, and treatment of oil-in-water emulsion using the carbon membrane is feasible and effective with the oil rejection efficiency being over 98%. Based on the modified Hermia's model, membrane fouling mechanisms were analyzed and resistance controlling factors of permeate flow were discussed. Under the present operating conditions, there is a switch of fouling mechanisms from the standard pore fouling to the cake filtration at small apparent flow rate and trans-membrane pressure difference. When the values of two parameters are raised, the intermediate pore fouling becomes dominant after the early period of cake filtration.

Cerebrospinal Fluid Flow in the Normal and Hydrocephalic Human Brain

Advances in magnetic resonance (MR) imaging techniques enable the accurate measurements of cerebrospinal fluid (CSF) flow in the human brain. In addition, image reconstruction tools facilitate the collection of patient-specific brain geometry data such as the exact dimensions of the ventricular and subarachnoidal spaces (SAS) as well as the computer-aided reconstruction of the CSF-filled spaces. The solution of the conservation of CSF mass and momentum balances over a finite computational mesh obtained from the MR images predict the patients' CSF flow and pressure field. Advanced image reconstruction tools used in conjunction with first principles of fluid mechanics allow an accurate verification of the CSF flow patters for individual patients. This paper presents a detailed analysis of pulsatile CSF flow and pressure dynamics in a normal and hydrocephalic patient. Experimental CSF flow measurements and computational results of flow and pressure fields in the ventricular system, the SAS and brain parenchyma are presented. The pulsating CSF motion is explored in normal and pathological conditions of communicating hydrocephalus. This paper predicts small transmantle pressure differences between lateral ventricles and SASs (approximately 10 Pa). The transmantle pressure between ventricles and SAS remains small even in the hydrocephalic patient (approximately 30 Pa), but the ICP pulsatility increases by a factor of four. The computational fluid dynamics (CFD) results of the predicted CSF flow velocities are in good agreement with Cine MRI measurements. Differences between the predicted and observed CSF flow velocities in the prepontine area point towards complex brain-CSF interactions. The paper presents the complete computational model to predict the pulsatile CSF flow in the cranial cavity.

Final report on the supplementary comparison Euromet.M.P-S2 (bilateral comparison) in the pressure range from 30 Pa to 7000 Pa

A bilateral comparison was carried out in order to test the degree of equivalence between the newly established pressure balances of the Czech Metrological Institute and the Physikalisch-Technische Bundesanstalt (PTB). The comparison was carried out without using a transfer standard, but with a differential capacitance diaphragm gauge as an indicator of the small differential pressure between the two pressure balances when the target pressures were generated in the two systems. The Czech Metrological Institute brought its force balanced piston gauge FPG by the DHI company to the site of the PTB pressure balance, which was a Furness Rosenberg system FRS 5 by the Furness company. In the range under comparison from 30 Pa to 7000 Pa full equivalence was obtained with the En value ranging from 0.01 to 0.47.Main text.To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by EUROMET, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).

Final Report on Key Comparison APMP.M.P-K5 in differential pressure from 1 Pa to 5000 Pa

This report describes the results of a key comparison of small differential pressure standards at two national metrology institutes (NMIs: NMIJ/AIST and MSL) that was carried out during the period May 2005 to October 2005 within the framework of the Asia-Pacific Metrology Programme (APMP) in order to determine their degrees of equivalence at pressures in the range 1 Pa to 5000 Pa. The differential pressures were compared at a line pressure of about 100 kPa (absolute). The pilot institute was the National Metrology Institute of Japan (NMIJ)/AIST. Both participating institutes used double pressure balances as their primary pressure standards. The transfer standard package consisted of three high-precision pressure transducers: one capacitance diaphragm gauge to provide high resolution at low differential pressures, and two resonant silicon gauges to provide the required calibration stability. The transfer standard was calibrated at the pilot institute (NMIJ/AIST) at the beginning and the end of the comparison. These results show that the transfer standard was sufficiently stable to meet the requirements of the comparison. The degrees of equivalence of the measurement standards were expressed quantitatively by two terms, deviations from the key comparison reference values and pairwise differences of their deviations. The differential pressure standards in the range 1 Pa to 5000 Pa of the two participating NMIs were found to be fully equivalent within their claimed uncertainties. The degrees of equivalence in this comparison were also transferred to the corresponding CCM key comparison, CCM.P-K5, and it is shown that the NMIJ values were equivalent to the CCM KCRV within the claimed uncertainties.Main text.To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCM, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).

Microfluidic culture platform for neuroscience research

This protocol describes the fabrication and use of a microfluidic device to culture central nervous system (CNS) and peripheral nervous system neurons for neuroscience applications. This method uses replica-molded transparent polymer parts to create miniature multi-compartment cell culture platforms. The compartments are made of tiny channels with dimensions of tens to hundreds of micrometers that are large enough to culture a few thousand cells in well-controlled microenvironments. The compartments for axon and somata are separated by a physical partition that has a number of embedded micrometer-sized grooves. After 3-4 days in vitro (DIV), cells that are plated into the somal compartment have axons that extend across the barrier through the microgrooves. The culture platform is compatible with microscopy methods such as phase contrast, differential interference microscopy, fluorescence and confocal microscopy. Cells can be cultured for 2-3 weeks within the device, after which they can be fixed and stained for immunocytochemistry. Axonal and somal compartments can be maintained fluidically isolated from each other by using a small hydrostatic pressure difference; this feature can be used to localize soluble insults to one compartment for up to 20 h after each medium change. Fluidic isolation enables collection of pure axonal fraction and biochemical analysis by PCR. The microfluidic device provides a highly adaptable platform for neuroscience research and may find applications in modeling CNS injury and neurodegeneration. This protocol can be completed in 1-2 days.

Oxygen permeation through a Ce 0.8Sm 0.2O 2− δ–La 0.8Sr 0.2CrO 3− δ dual-phase composite membrane

A composite of oxygen ion conducting oxide Ce 0.8Sm 0.2O 2− δ (60 vol.%) and electron conducting oxide La 0.8Sr 0.2CrO 3− δ was prepared by sintering a powder compact at a temperature of 1550 °C. No significant reaction between the two constituent oxides was observed under preparation and oxygen permeation conditions. Appreciable oxygen permeation fluxes through the composite membrane were measured at elevated temperatures with one side of it exposed to the ambient air and the other side to a flowing helium gas stream. The oxygen flux initially increased with time, and took a long time to reach a steady value. A steady oxygen permeation flux as high as 1.4 × 10 −7 mol cm −2 s −1 was obtained with a 0.3 mm thick membrane at 950 °C under a relatively small oxygen partial pressure difference of 0.21 bar/0.0092 bar. It was revealed that the overall oxygen permeation process was mainly limited by the transport in the bulk of the membrane in the range of the membrane thickness greater than ∼1.0 mm, and the limitation by the surface oxygen exchange came into play at reduced thickness of ∼0.6 mm.

Compression Therapy: Effects of Posture and Application Techniques on Initial Pressures Delivered by Bandages of Different Physical Properties

Objective To define the pressures and gradients achieved by different bandages when applied by alternative bandaging techniques. Methods An experienced bandager applied six bandages to the same leg of a volunteer using three application techniques. Pressure measurements were taken at the ankle, gaiter, calf and upper calf in three postures. Results All bandages gave consistent pressures with all standard deviations falling below 7 mmHg. The percentage increase in pressure from resting leg to standing was inversely related to bandage elasticity. Pressures were similar at the upper calf among the bandages for each application technique in each posture (differences <10 mmHg). Small differences in pressure among the bandages (4–15 mmHg) occurred at the ankle for the resting leg with a reduction in pressure between 6 and 63% at the upper calf compared to the ankle. These differences in ankle pressure were more marked on sitting (differences 15–18 mmHg) and standing (differences 15–27 mmHg), which resulted in substantial differences in gradients. Conclusions Striking variations in pressures and gradients were observed between bandages of different physical properties applied using alternative application techniques. In order to achieve clinical benefits without tissue damage, it is essential that the therapist appreciates how a bandage will react with a specific application technique.