Hyperpolarized 3He magnetic resonance imaging ventilation defects in asthma: relationship to airway mechanics

In patients with asthma, magnetic resonance imaging (MRI) provides direct measurements of regional ventilation heterogeneity, the etiology of which is not well-understood, nor is the relationship of ventilation abnormalities with lung mechanics. In addition, respiratory resistance and reactance are often abnormal in asthmatics and the frequency dependence of respiratory resistance is thought to reflect ventilation heterogeneity. We acquiredMRIventilation defect maps, forced expiratory volume in one-second (FEV1), and airways resistance (Raw) measurements, and used a computational airway model to explore the relationship of ventilation defect percent (VDP) with simulated measurements of respiratory system resistance (Rrs) and reactance (Xrs).MRIventilation defect maps were experimentally acquired in 25 asthmatics before, during, and after methacholine challenge and these were nonrigidly coregistered to the airway tree model. Using the model coregistered to ventilation defect maps, we narrowed proximal (9th) and distal (14th) generation airways that were spatially related to theMRIventilation defects. The relationships forVDPwith Raw measured using plethysmography (r = 0.79), and model predictions of Rrs\u3e14(r = 0.91,P \u3c 0.0001) and Rrs\u3e9(r = 0.88,P \u3c 0.0001) were significantly stronger (P = 0.005;P = 0.03, respectively) than withFEV1(r = -0.68,P = 0.0001). The slopes for the relationship ofVDPwith simulated lung mechanics measurements were different (P \u3c 0.0001); among these, the slope for theVDP-Xrs0.2relationship was largest, suggesting thatVDPwas dominated by peripheral airway heterogeneity in these patients. In conclusion, as a first step toward understanding potential links between lung mechanics and ventilation defects, impedance predictions were made using a computational airway tree model with simulated constriction of airways related to ventilation defects measured in mild-moderate asthmatics

Out-of-autoclave manufacturing of aerospace representative parts

The use of carbon fibre reinforced composites for aerospace structures has seen a high increase in recent years, and is still growing. The high stiffness-to-weight ratio of these materials makes them ideal for primary structures on airplanes, satellites, and spacecrafts. Nevertheless, the manufacturing of composites remains very costly since it requires equipment investment such as an autoclave, and very qualified workers. Out-of-autoclave manufacturing technology is very promising since it only requires a traditional oven, while still aiming at similar part quality. However, the absence of positive pressure compared with an autoclave makes it more difficult to achieve low porosity parts. This research investigates the manufacturing of complex features with out-of autoclave prepreg technology. The features studied are tight-radius corners with a curvature change, and ply drop-offs. Ply drop-offs tests were conducted to identify if porosity is higher at ply terminations. In corners, the bagging arrangement was modified to achieve the most uniform thickness in areas of curvature change, even with small radii. The conclusions from these studies provided us with guidelines to manufacture larger representative parts, which included these features. The representative parts were tested for porosity, thickness uniformity, mechanical performance, and glass transition temperature(Tg). A total of four representative parts were manufactured with out-of-autoclave technology, and one more was manufactured with an autoclave to allow for a proper comparison between the two processes. The materials used were MTM45-1 5 harness satin and CYCOM5320 plain weave for the out-of-autoclave parts,and CYCOM5276-1 plain weave for the autoclave part. The effect of ply dropoffs on porosity was found to be negligible. Thickness deviation in corners was attributed to a combination of consumable bridging, prepreg's bulk factor and inter-ply shear. Overall, out-of-autoclave prepregs showed performance similar to autoclave prepregs.L'utilisation de matériaux composites en fibres de carbone pour des structures aéronautiques a connu une croissance rapide ces dernières années, et continue de croitre. Le rapport raideur/masse de ce type de matériaux en fait une solution idéale pour les structures primaires d'avions, de satellites, ou de navettes spatiales. Toutefois, la fabrication de ces pièces en composites demeure extrêmement couteuse puisqu'elle nécessite de lourds investissements d'équipement tels que l'acquisition d'un autoclave, ainsi que de la main-d'oeuvre qualifiée. La technologie hors autoclave semble très prometteuse puisqu'elle ne requiert que l'utilisation d'un four traditionnel, tout en visant à obtenir des pièces de qualité similaire. Cependant, l'absence de pression extérieure provenant de l'autoclave rend plus délicate l'obtention de pièces ayant une faible porosité. Cette recherche a pour thème la fabrication d'éléments complexes avec la technologie hors autoclave. Les éléments étudiés sont des angles convexes et concaves ayant de faibles rayons de courbure, ainsi que des plis partiels. Des tests sur les plis partiels ont été réalisés pour déterminer si ils sont associés à une augmentation de la porosité. Dans les angles, l'arrangement des consommables a été modifié pour obtenir l'épaisseur la plus uniforme possible dans les zones de changement de courbure, et cela même pour de faibles rayons. Les conclusions de ces tests nous ont permis de considérer la fabrication de pièces représentatives de plus grande taille, et qui contiennent les éléments précédemment étudiés. Les pièces représentatives ont été testées pour déterminer leur niveau de porosité, l'uniformité de leur épaisseur, leur performance mécanique, et leur température de transition vitreuse. Au total, quatre pièces représentatives ont été fabriquées par technologie hors autoclave, et une a été fabriquée dans un autoclave afin de permettre une comparaison de bon aloi entre ces deux procédés de fabrication. Les matériaux utilisés pour cette recherche étaient du MTM45-1 5 harness satin et du CYCOM5320 plain weave pour les pièces hors autoclave, ainsi que du CYCOM5276-1 plain weave pour la pièce autoclave. La présence de plis partiels n'a pas été associable à une augmentation notable de la porosité. L'uniformité d'épaisseur s'est révélée être une combinaison de pontage des consommables, du facteur de foisonnement du pré-imprégné, et du cisaillement entre les plis de fibre. Globalement, les pré-imprégnés hors autoclave ont montré des performances similaires aux pré-imprégnés autoclave

Failure of Body Plethysmography in Bronchial-asthma

To determine whether acute changes in lung volumes in asthma are accurately measured by body plethysmography, we induced acute changes in lung mechanics with acetylcholine in nine asthmatic patients and with salbutamol in six others. Total lung capacity (TLC) was measured with a body plethysmograph and derived from mouth pressure vs. box volume (Vbox) changes (TLCm) or esophageal pressure vs. Vbox changes (TLCes). In six patients (4 after acetylcholine) TLCm was significantly (P less than 0.05) different from prechallenge values (differences ranged from 0.29 to 1.55 liters), but TLCes did not change. In three additional patients both TLCm (mean difference 0.62 liter) and TLCes (mean difference 0.43 liter) changed (P less than 0.05), but no changes occurred in six others. An electrical analog of the lung demonstrates in the presence of intrathoracic airway obstruction overestimation of thoracic gas volume and TLC. This is due to the presence of a compliant extrathoracic airway that acts as a shunt impedance. The magnitude of the overestimation of TGV appears to depend on the distensibility of the extrathoracic airway and the degree of airway obstruction. We conclude that the plethysmographic method may introduce important errors in lung volume measurements in the obstructive syndrome, especially a severe one. Some of previously reported acute increases in TLC in asthmatics may be artifactual. </jats:p