A comparison of methods to identify open-lung PEEP

Purpose: Many methods exist in the literature for identifying PEEP to set in ARDS patients following a lung recruitment maneuver (RM). We compared ten published parameters for setting PEEP following a RM. Methods: Lung injury was induced by bilateral lung lavage in 14 female Dorset sheep, yielding a PaO(2) 100-150 mmHg at F(I)O(2) 1.0 and PEEP 5 cmH(2)O. A quasi-static P-V curve was then performed using the supersyringe method; PEEP was set to 20 cmH(2)O and a RM performed with pressure control ventilation (inspiratory pressure set to 40-50 cmH(2)O), until PaO(2) + PaCO(2) > 400 mmHg. Following the RM, a decremental PEEP trial was performed. The PEEP was decreased in 1 cmH(2)O steps every 5 min until 15 cmH(2)O was reached. Parameters measured during the decremental PEEP trial were compared with parameters obtained from the P-V curve. Results: For setting PEEP, maximum dynamic tidal respiratory compliance, maximum PaO(2), maximum PaO(2) + PaCO(2), and minimum shunt calculated during the decremental PEEP trial, and the lower Pflex and point of maximal compliance increase on the inflation limb of the P-V curve (Pmci,i) were statistically indistinguishable. The PEEP value obtained using the deflation upper Pflex and the point of maximal compliance decrease on the deflation limb were significantly higher, and the true inflection point on the inflation limb and minimum PaCO(2) were significantly lower than the other variables. Conclusion: In this animal model of ARDS, dynamic tidal respiratory compliance, maximum PaO(2), maximum PaO(2) + PaCO(2), minimum shunt, inflation lower Pflex and Pmci,i yield similar values for PEEP following a recruitment maneuver.

Numerical simulation of dendrite growth during solidification

A comprehensive probabilistic model for simulating dendrite morphology and investigating dendritic growth kinetics during solidification has been developed, based on a modified Cellular Automaton (mCA) for microscopic modeling of nucleation, growth of crystals and solute diffusion. The mCA model numerically calculated solute redistribution both in the solid and liquid phases, the curvature of dendrite tips and the growth anisotropy. This modeling takes account of thermal, curvature and solute diffusion effects. Therefore, it can simulate microstructure formation both on the scale of the dendrite tip length. This model was then applied for simulating dendritic solidification of an Al-7%Si alloy. Both directional and equiaxed dendritic growth has been performed to investigate the growth anisotropy and cooling rate on dendrite morphology. Furthermore, the competitive growth and selection of dendritic crystals have also investigated.

N-methylation of diamino-substituted macrocyclic complexes: Intermolecular reactions

Two N-based isomeric copper(II) complexes of the macrocycle trans-6,13-dimethyl-6,13-bis(dimethylamino)1,4,8,11-tetraazacyclotetradecane (L(3)) have been synthesized and characterised spectroscopically and structurally: alpha-[CuL(3)(OH2)(2)]Cl-2, monoclinic, space group C2/m, a = 12.908(4), b = 12.433(2), c = 7.330(2) Angstrom, beta = 105.87(2)degrees, Z = 2; beta-[CuL(3)(OClO3)(2)]. 2H(2)O, monoclinic, space group P2(1)/c, a = 9.708(3), b = 9.686(3), c = 14.202(4) Angstrom, beta = 106.17(1)degrees, Z = 2. The two isomers exhibit very similar co-ordination spheres but significantly different visible electronic maxima. This difference is attributed to an intramolecular N ... H contact between the pendant dimethylamino group and an adjacent secondary amine H atom.

Dynamic strain measurement using piezoelectric polymer film

Piezoelectric polymers have been used to form the basis of dynamic strain gauges for the detection of stress waves. The linearity of response was tested using a split Hopkinson pressure bar arrangement. The results obtained illustrate the effectiveness of piezoelectric film strain gauges in the measurement of axial stress waves.

Turbulent spots in boundary layers in a free-piston shock-tunnel flow

In this paper, experiments to detect turbulent spots in the transitional boundary layers, formed on a flat plate in a free-piston shock tunnel how, are reported. Experiments indicate that thin-film heat-transfer gauges are suitable for identifying turbulent-spot activity and can be used to identify parameters such as the convection rate of spots and the intermittency of turbulence.

Prediction of impact forces in a vibratory ball mill using an inverse technique

To understand the dynamic mechanisms of the mechanical milling process in a vibratory mill, it is necessary to determine the characteristics of the impact forces associated with the collision events. However, it is difficult to directly measure the impact force in an operating mill. This paper describes an inverse technique for the prediction of impact forces from acceleration measurements on a vibratory ball mill. The characteristics of the vibratory mill have been investigated by the modal testing technique, and its system modes have been identified. In the modelling of the system vibration response to the impact forces, two modal equations have been used to describe the modal responses. The superposition of the modal responses gives rise to the total response of the system. A method based on an optimisation approach has been developed to predict the impact forces by minimising the difference between the measured acceleration of the vibratory ball mill and the predicted acceleration from the solution of the modal equations. The predicted and measured impact forces are in good agreement. Copyright (C) 1996 Elsevier Science Ltd.

Discrete and continuous models for dry masonry columns

The dynamic response of dry masonry columns can be approximated with finite-difference equations. Continuum models follow by replacing the difference quotients of the discrete model by corresponding differential expressions. The mathematically simplest of these models is a one-dimensional Cosserat theory. Within the presented homogenization context, the Cosserat theory is obtained by making ad hoc assumptions regarding the relative importance of certain terms in the differential expansions. The quality of approximation of the various theories is tested by comparison of the dispersion relations for bending waves with the dispersion relation of the discrete theory. All theories coincide with differences of less than 1% for wave-length-block-height (L/h) ratios bigger than 2 pi. The theory based on systematic differential approximation remains accurate up to L/h = 3 and then diverges rapidly. The Cosserat model becomes increasingly inaccurate for L/h < 2 pi. However, in contrast to the systematic approximation, the wave speed remains finite. In conclusion, considering its relative simplicity, the Cosserat model appears to be the natural starting point for the development of continuum models for blocky structures.

Structural and electron self-exchange rate variations in isomeric (hexaamine)cobalt(III/II) complexes

The syntheses and characterisation of the new macrocyclic hexaamine trans-(5(S),7(S),12(R),14(R)-tetramethyl)-1,4,8,11-tetraazacyclotetradecane-6,13-diamine (L-6) and its Co-III complex are reported. The X-ray crystal structural analyses of [CoL6]Cl-2(ClO4) [monoclinic, space group C2/c, a = 16.468(3) Angstrom, b = 9.7156(7) Angstrom, c = 15.070(3) Angstrom, beta = 119.431(8)degrees, Z = 4] and the closely related cis-diamino-substituted macrocyclic complex [CoL2](ClO4)(3) . 2H(2)O (L-2 = cis-6,13-dimethyl-1,4,8,11-tetraazacyclotetradecane-6,13-diamine) [orthorhombic, space group Pna2(1), a = 16.8220(8) Angstrom, b = 10.416(2) Angstrom, c = 14.219(3) Angstrom, Z = 4] reveal significant variations in the observed Co-N bond lengths and coordination geometries, which may be attributed to the trans or cis disposition of the pendent primary amines. The Co-III/II self-exchange electron transfer rate constants for these and other closely related hexaamines have been determined, and variations of some 2 orders of magnitude are found between pairs of trans and cis isomeric Co-III complexes.

Comparison Between Perfadex and Locally Manufactured Low-Potassium Dextran Solution for Pulmonary Preservation in an Ex Vivo Isolated Lung Perfusion Model

Introduction. Lung tranplantation, a consolidated treatment for end-stage lung disease, utilizes preservation solutions, such as low potassium dextran (LPD), to mitigate ischemia reperfusion injury. We sought the local development of LPD solutions in an attempt to facilitate access and enhance usage. We also sought to evaluate the effectiveness of a locally manufactured LPD solution in a rat model of ex vivo lung perfusion. Methods. We randomized the following groups \?\adult of male Wistar rats (n = 25 each): Perfadex (LPD; Vitro life, Sweden); locally manufactured LPD-glucose (LPDnac) (Farmoterapica, Brazil), and normal saline solution (SAL) with 3 ischemic times (6, 12, and 24 hours). The harvested heart lung blocks were flushed with solution at 4 C. After storage, the blocks were connected to an IL-2 Isolated Perfused Rat or Guinea Pig Lung System (Harvard Apparatus) and reperfused with homologous blood for 60 minutes. Respiratory mechanics, pulmonary artery pressure, perfusate blood gas analysis, and lung weight were measured at 10-minute intervals. Comparisons between groups and among ischemic times were performed using analysis of variance with a 5% level of significance. Results. Lungs preserved for 24 hours were nonviable and therefore excluded from the analysis. Those preserved for 6 hours showed better ventilatory mechanics when compared with 12 hours. The oxygenation capacity was not different between lungs flushed with LPD or LPDnac, regardless of the ischemic time. SAL lungs showed higher PCO(2) values than the other solutions. Lung weight increased over time during perfusion; however, there were no significant differences among the tested solutions (LPD, P = .23; LPDnac, P = .41; SAL, P = .26). We concluded that the LPDnac solution results in gas exchange were comparable to the original LPD (Perfadex); however ventilatory mechanics and edema formation were better with LPD, particularly among lungs undergoing 6 hours of cold ischemia.

A continuum model for periodic two-dimensional block structures

A continuum model for regular block structures is derived by replacing the difference quotients of the discrete equations by corresponding differential quotients. The homogenization procedure leads to an anisotropic Cosserat Continuum. For elastic block interactions the dispersion relations of the discrete and the continuous models are derived and compared. Yield criteria for block tilting and sliding are formulated. An extension of the theory for large deformation is proposed. (C) 1997 by John Wiley & Sons, Ltd.

A compact shock-assisted free-piston driver for impulse facilities

A free-piston driver that employs entropy-raising shock processes with diaphragm rupture has been constructed, which promises significant theoretical advantages over isentropic compression. Results from a range of conditions with helium and argon driver gases are reported. Significant performance gains were achieved in some test cases. Heat losses are shown to have a strong effect on driver processes. Measurements compare well with predictions from a quasi-one-dimensional numerical code.

The subcycled Newmark algorithm

The popular Newmark algorithm, used for implicit direct integration of structural dynamics, is extended by means of a nodal partition to permit use of different timesteps in different regions of a structural model. The algorithm developed has as a special case an explicit-explicit subcycling algorithm previously reported by Belytschko, Yen and Mullen. That algorithm has been shown, in the absence of damping or other energy dissipation, to exhibit instability over narrow timestep ranges that become narrower as the number of degrees of freedom increases, making them unlikely to be encountered in practice. The present algorithm avoids such instabilities in the case of a one to two timestep ratio (two subcycles), achieving unconditional stability in an exponential sense for a linear problem. However, with three or more subcycles, the trapezoidal rule exhibits stability that becomes conditional, falling towards that of the central difference method as the number of subcycles increases. Instabilities over narrow timestep ranges, that become narrower as the model size increases, also appear with three or more subcycles. However by moving the partition between timesteps one row of elements into the region suitable for integration with the larger timestep these the unstable timestep ranges become extremely narrow, even in simple systems with a few degrees of freedom. As well, accuracy is improved. Use of a version of the Newmark algorithm that dissipates high frequencies minimises or eliminates these narrow bands of instability. Viscous damping is also shown to remove these instabilities, at the expense of having more effect on the low frequency response.

Aerobic training reverses airway inflammation and remodelling in an asthma murine model

Aerobic training (AT) decreases dyspnoea and exercise-induced bronchospasm, and improves aerobic capacity and quality of life; however, the mechanisms for such benefits remain poorly understood. The aim of the present study was to evaluate the AT effects in a chronic model of allergic lung inflammation in mice after the establishment of airway inflammation and remodelling. Mice were divided into the control group, AT group, ovalbumin (OVA) group or OVA+AT group and exposed to saline or OVA. AT was started on day 28 for 60 min five times per week for 4 weeks. Respiratory mechanics, specific immunoglobulin (Ig)E and IgG(1), collagen and elastic fibres deposition, smooth muscle thickness, epithelial mucus, and peribronchial density of eosinophils, CD3+ and CD4+, IL-4, IL-5, IL-13, interferon-gamma, IL-2, IL-1ra, IL-10, nuclear factor (NF)-kappa B and Foxp3 were evaluated. The OVA group showed an increase in IgE and IgG1, eosinophils, CD3+, CD4+, IL-4, IL-5, IL-13, NF-kappa B, collagen and elastic, mucus synthesis, smooth muscle thickness and lung tissue resistance and elastance. The OVA+AT group demonstrated an increase of IgE and IgG(1), and reduction of eosinophils, CD3+, CD4+, IL-4, IL-5, IL-13, NF-kappa B, airway remodelling, mucus synthesis, smooth muscle thickness and tissue resistance and elastance compared with the OVA roup (p < 0.05). The OVA+AT group also showed an increase in IL-10 and IL-1ra (p < 0.05), independently of Foxp3. AT reversed airway inflammation and remodelling and T-helper cell 2 response, and improved respiratory mechanics. These results seem to occur due to an increase in the expression of IL-10 and IL-1ra and a decrease of NF-kappa B.

Prone position prevents regional alveolar hyperinflation and mechanical stress and strain in mild experimental acute lung injury

Prone position may delay the development of ventilator-induced lung injury (VILI), but the mechanisms require better elucidation. In experimental mild acute lung injury (ALI), arterial oxygen partial pressure (Pa(O2)), lung mechanics and histology, inflammatory markers [interleukin (IL)-6 and IL-1 beta], and type III procollagen (PCIII) mRNA expressions were analysed in supine and prone position. Wistar rats were randomly divided into two groups. In controls, saline was intraperitoneally injected while ALI was induced by paraquat. After 24-h, the animals were mechanically ventilated for 1-h in supine or prone positions. In ALI, prone position led to a better blood flow/tissue ratio both in ventral and dorsal regions and was associated with a more homogeneous distribution of alveolar aeration/tissue ratio reducing lung static elastance and viscoelastic pressure, and increasing end-expiratory lung volume and Pa(O2). PCIII expression was higher in the ventral than dorsal region in supine position, with no regional changes in inflammatory markers. In conclusion, prone position may protect the lungs against VILI, thus reducing pulmonary stress and strain. (C) 2009 Elsevier B.V. All rights reserved.

Effects of frequency and inspiratory plateau pressure during recruitment manoeuvres on lung and distal organs in acute lung injury

To evaluate the effects of frequency and inspiratory plateau pressure (Pplat) during recruitment manoeuvres (RMs) on lung and distal organs in acute lung injury (ALI). We studied paraquat-induced ALI rats. At 24 h, rats were anesthetized and RMs were applied using continuous positive airway pressure (CPAP, 40 cmH(2)O/40 s) or three-different sigh strategies: (a) 180 sighs/h and Pplat = 40 cmH(2)O (S180/40), (b) 10 sighs/h and Pplat = 40 cmH(2)O (S10/40), and (c) 10 sighs/h and Pplat = 20 cmH(2)O (S10/20). S180/40 yielded alveolar hyperinflation and increased lung and kidney epithelial cell apoptosis as well as type III procollagen (PCIII) mRNA expression. S10/40 resulted in a reduction in epithelial cell apoptosis and PCIII expression. Static elastance and alveolar collapse were higher in S10/20 than S10/40. The reduction in sigh frequency led to a protective effect on lung and distal organs, while the combination with reduced Pplat worsened lung mechanics and histology.