What Causes Uneven Aerosol Deposition in the Bronchoconstricted Lung? A Quantitative Imaging Study

BACKGROUND: A previous PET-CT imaging study of 14 bronchoconstricted asthmatic subjects showed that peripheral aerosol deposition was highly variable among subjects and lobes. The aim of this work was to identify and quantify factors responsible for this variability. METHODS: A theoretical framework was formulated to integrate four factors affecting aerosol deposition: differences in ventilation, in how air vs. aerosol distribute at each bifurcation, in the fraction of aerosol escaping feeding airways, and in the fraction of aerosol reaching the periphery that is exhaled. These factors were quantified in 12 of the subjects using PET-CT measurements of relative specific deposition sD*, relative specific ventilation sV* (measured with dynamic PET or estimated as change in expansion between two static HRCTs), average lobar expansion FVOL, and breathing frequency measured during aerosol inhalation fN. RESULTS: The fraction of the variance of sD* explained by sV* (0.38), by bifurcation effects (0.38), and by differences in deposition along feeding airways (0.31) were similar in magnitude. We could not directly estimate the contribution of aerosol that was exhaled. Differences in expansion did not explain any fraction of the variability in sD* among lobes. The dependence of sD* on sV* was high in subjects breathing with low fN, but weakened among those breathing faster. Finally, sD*/sV* showed positive dependence on FVOL among low fN subjects, while the dependence was negative among high fN subjects. CONCLUSION: The theoretical framework allowed us to analyze experimentally measured aerosol deposition imaging data. When considering bronchoconstricted asthmatic subjects, a dynamic measurement of ventilation is required to evaluate its effect on aerosol transport. The mechanisms behind the identified effects of fN and FVOL on aerosol deposition need further study and may have important implications for aerosol therapy in subjects with heterogeneous ventilation. Keywords: aerosol deposition; asthma; bronchoconstriction; escape fractions; sedimentation; ventilationNational Institutes of Health (U.S.) (Award R01HL68011

Regional Ventilation and Aerosol Deposition with Helium-Oxygen in Bronchoconstricted Asthmatic Lungs

Background: Theoretical models suggest that He-O₂ as carrier gas may lead to more homogeneous ventilation and aerosol deposition than air. However, these effects have not been clinically consistent and it is unclear why subjects may or may not respond to the therapy. Here we present 3D-imaging data of aerosol deposition and ventilation distributions from subjects with asthma inhaling He-O₂ as carrier gas. The data are compared with those that we previously obtained from a similar group of subjects inhaling air. Methods: Subjects with mild-to-moderate asthma were bronchoconstricted with methacholine and imaged with PET-CT while inhaling aerosol carried with He-O₂. Mean-normalized-values of lobar specific ventilation sV∗ and deposition sD∗ were derived and the factors affecting the distribution of sD∗ were evaluated along with the effects of breathing frequency (f) and regional expansion (FVOL). Results: Lobar distributions of sD∗ and sV∗ with He-O₂ were not statistically different from those previously measured with air. However, with He-O₂ there was a larger number of lobes having sV∗ and sD∗ closer to unity and, in those subjects with uneven deposition distributions, the correlation of sD∗ with sV∗ was on average higher (p < 0.05) in He-O₂ (0.84 ± 0.8) compared with air (0.55 ± 0.28). In contrast with air, where the frequency of breathing during nebulization was associated with the degree of sD∗-sV∗ correlation, with He-O₂ there was no association. Also, the modulation of f on the correlation between FVOL and sD∗/sV∗ in air, was not observed in He-O₂. Conclusion: There were no differences in the inter-lobar heterogeneity of sD∗ or sV∗ in this group of mild asthmatic subjects breathing He-O₂ compared with patients previously breathing air. Future studies, using these personalized 3D data sets as input to CFD models, are needed to understand if, and for whom, breathing He-O₂ during aerosol inhalation may be beneficial.National Institutes of Health (U.S.) (Award R01HL68011

Le système d’observation et de recherche en environnement côtier de Thau – RECThau

International audienceCe Système d’Observation (SO) a été créé en 2009 au démarrage de l’OSUOREME à Montpellier. Il avait le double objectif de 1.structurer et pérenniserdes observations dans la lagune et sur la côte jusqu’alors ponctuelles voiresporadiques et 2. initier une coordination des différentes observations sur lelittoral languedocien dans l’espace géographique de la lagune de Thau afind’engendrer de nouvelles collaborations aussi bien en termes méthodologiquesque de nouveaux projets de recherche.Depuis 2015, le SO affiche une nouvelle appellation et une nouvellestructuration en trois Tâches d’Observation (TO) :- la TO du Bassin-Versant de la lagune de Thau (TO BV-Thau) : regroupe lesobservations météo-hydrologiques sur le bassin versant de la lagune de Thau.Ces observations sont mises en place depuis plus de 15 ans sur la Vène,principal contributeur du bassin.- la TO de la lagune de Thau (TO Suivi-Thau) : regroupe les observations deparamètres météorologiques et de paramètres physico-chimiques etbiologiques effectuées dans la colonne d’eau de la lagune de Thau. Cette TOest en partie en relation avec les expérimentations effectuées dans lesmésocosmes in situ de MEDIMEER installés sur la lagune de Thau,- la TO côtière au large de la lagune de Thau et sur le plateau continental enface de la ville de Sète (SOMLIT-Sète) : regroupe les observations desvariables physico-chimiques et biologiques sous 30 m de fond au large deSète, jusqu’alors dénommée Suivi-Côte. Elle a intégré le réseau SOMLIT(Service national d’Observation du Milieu LITtoral) en 2015. Les mesures sefont également à Haute Fréquence sur la station BESSète et elle est ainsimembre fondateur du réseau COAST-H

Impact of storms and floods episodes on primary production in an exploited coastal zone (Thau lagoon, south of France): Coupled hydrodynamic-biogeochemistry modeling approach.

International audienceThe authors collaborate within the SO RECThau (Service of Observation and Research incoastal Environment of Thau) of the OSU OREME. They find themselves here on a projectof hydro-biogeochemical numerical modelling complementary of their activities ofobservations. Illustrated on the period of the RESTHAU campaign (November 2008), theaim is to evaluate the impact of storms and floods episodes on primary production.The coupled model Symphonie-ECO3M was implemented on a fairly original computinggrid encompassing the Thau lagoon, the canals, the foreshore and open sea to the offshorezone. The hydrodynamic model is coupled to the ECO3M model based on mechanisticformulations of biological processes. The model uses 35 state variables and reproduces acomplex planktonic ecosystem with several primary producers and several consumers. Thebiochemical cycles of the biogenic elements (C, N, P, Si) are managed by the model.Owing to field data, the November 2008 storm period was investigated. The first resultsshow no increase in primary production during and after the storm in spite of an enrichmentof the lagoon in nutrients which seems to indicate a limitation by light or temperature. Therole of predation by oysters (more than 10 000 tonnes in the lagoon) is also investigated bycomparing the modified model integrating this compartment with mesocosms results