Significant Increase In Deposition Research Articles

Towards whole-lung simulations of aerosol deposition: A model of the deep lung

In silico methods can be used to estimate regional deposition of inhaled aerosols in regions of the lung that are inaccessible by direct measurements. Knowledge of deposited dose is important for assessing the efficacy of inhaled pharmaceutical aerosols or the impact from exposure to environmental pollutants. Although patient-specific geometries of the upper airways are widely used nowadays, insufficient imaging resolution precludes the reconstruction of 3D models of the deeper lung generations. In the present study, the 3D model of the deep lung (DLM) we have previously developed is utilised to examine the effects of breathing profile, breathhold and gravity orientation on deposition in the deep airways. The objective is to assess whether a small number of DLMs could be utilised to provide deposition predictions in the entire peripheral lung, with the ultimate goal being the integration of DLM with imaging-derived models of the upper airways for whole-lung deposition predictions. It is found that deposition in the respiratory region during deep breathing increases remarkably compared to quiet breathing since particles avoid retention in the conducting generations. Significant increases in deposition are recorded when breathhold is employed, with approximately 70% rise in total deposition of 1–2 μm particles. Our findings indicate that the breathing maneuver can be used to target different deposition sites in the deep lung: deep inhalation followed by breathhold should be employed to achieve higher deposition in the respiratory region, whereas quiet inhalation followed by breathhold is recommended when targeting the deep conducting airways. Small differences in deposition during quiet inhalation are observed when the DLM is placed in seven different orientations relative to gravity. These differences are further reduced when realistic angle distributions are utilised for each of the five lung lobes and angle-weighted deposition fractions are compared. Our findings suggest that a small number of DLMs along with the distribution of gravity angles of an upper airway model could be employed to provide deposition estimates in the deep lung.

Colloidal deposition on polymer-brush-coated NF membranes

Fouling control remains a challenge in membrane separation. Here, nanofiltration (NF) membranes have been modified with poly-N-iso-propylacrylamide (PNIPAM) brushes, fabricated using surface-initiated atom transfer radical polymerization (ATRP). PNIPAM, a thermo-responsive polymer, exhibits a phase transition at its lower critical solution temperature (LCST) of ∼32 °C in DI water, which reduces to ∼20 °C at high-ionic strength. Direct microscopic observation was employed to investigate, in-situ, the deposition and release patterns and kinetics of colloidal fouling on NF membranes with and without a PNIPAM brush layer. Membrane surfaces were characterized by atomic force microscopy (AFM), X-ray Photoelectron Spectroscopy (XPS), and attenuated total reflection–Fourier transform infrared (ATR-FTIR) analysis. Changes in surface chemistry and morphology confirmed the grafting of PNIPAM with a rougher surface morphology. The permeate flux of grafted membranes with DI water at ∼20 °C and ∼40 °C indicate reversible conformational changes of PNIPAM. Cross-flow experiments revealed that even though the surface hydrophobicity of the PNIPAM-grafted membranes increased, the brush-coated membrane surfaces hinder particle deposition regardless of particle surface charge, exhibiting considerably lower deposition, compared to the unmodified membrane. Deposition was lower, for both membranes, in the case of negatively charged particles. When the particles had a small positive charge, a significant increase in deposition was observed for the unmodified membrane, compared with the modified membrane, presumably due to the former’s larger negative charge. However, particles, once deposited, could generally not be removed by physical rinsing, nor – in the case of the PNIPAM-coated membranes – by switching polymer conformation. Nevertheless, the results of the direct observation can provide valuable insight for further improving fouling-resistant membranes based on polymer brush coatings.

A computer model for the simulation of nanoparticle deposition in the alveolar structures of the human lungs.

According to epidemiological and experimental studies, inhalation of nanoparticles is commonly believed as a main trigger for several pulmonary dysfunctions and lung diseases. Concerning the transport and deposition of such nano-scale particles in the different structures of the human lungs, some essential questions are still in need of a clarification. Therefore, main objective of the study was the simulation of nanoparticle deposition in the alveolar region of the human respiratory tract (HRT). Respective factors describing the aerodynamic behavior of spherical and non-spherical particles in the inhaled air stream (i.e., Cunningham slip correction factors, dynamic shape factors, equivalent-volume diameters, aerodynamic diameters) were computed. Alveolar deposition of diverse nanomaterials according to several known mechanisms, among which Brownian diffusion and sedimentation play a superior role, was approximated by the use of empirical and analytical formulae. Deposition calculations were conducted with a currently developed program, termed NANODEP, which allows the variation of numerous input parameters with regard to particle geometry, lung morphometry, and aerosol inhalation. Generally, alveolar deposition of nanoparticles concerned for this study varies between 0.1% and 12.4% during sitting breathing and between 2.0% and 20.1% during heavy-exercise breathing. Prolate particles (e.g., nanotubes) exhibit a significant increase in deposition, when their aspect ratio is enhanced. In contrast, deposition of oblate particles (e.g., nanoplatelets) is remarkably declined with any reduction of the aspect ratio. The study clearly demonstrates that alveolar deposition of nanoparticles represents a topic certainly being of superior interest for physicists and respiratory physicians in future.

Gelatinase Contributes to the Pathogenesis of Endocarditis Caused by Enterococcus faecalis

The Gram-positive pathogen Enterococcus faecalis is a leading agent of nosocomial infections, including urinary tract infections, surgical site infections, and bacteremia. Among the infections caused by E. faecalis, endocarditis remains a serious clinical manifestation and unique in that it is commonly acquired in a community setting. Infective endocarditis is a complex disease, with many host and microbial components contributing to the formation of bacterial biofilm-like vegetations on the aortic valve and adjacent areas within the heart. In the current study, we compared the pathogenic potential of the vancomycin-resistant E. faecalis V583 and three isogenic protease mutants (ΔgelE, ΔsprE, and ΔgelE ΔsprE mutants) in a rabbit model of enterococcal endocarditis. The bacterial burdens displayed by GelE(-) mutants (ΔgelE and ΔgelE ΔsprE mutants) in the heart were significantly lower than those of V583 or the SprE(-) mutant. Vegetations on the aortic valve infected with GelE(-) mutants (ΔgelE and ΔgelE ΔsprE mutants) also showed a significant increase in deposition of fibrinous matrix layer and increased chemotaxis of inflammatory cells. In support of a role for proteolytic modulation of the immune response to E. faecalis, we also demonstrate that GelE can cleave the anaphylatoxin complement C5a and that this proteolysis leads to decreased neutrophil migration in vitro. In vivo, a decreased heterophil (neutrophil-like cell) migration was observed at tissue sites infected with GelE-producing strains but not at those infected with SprE-producing strains. Taken together, these observations suggest that of the two enterococcal proteases, gelatinase is the principal mediator of pathogenesis in endocarditis.

Over three millennia of mercury pollution in the Peruvian Andes

We present unambiguous records of preindustrial atmospheric mercury (Hg) pollution, derived from lake-sediment cores collected near Huancavelica, Peru, the largest Hg deposit in the New World. Intensive Hg mining first began ca. 1400 BC, predating the emergence of complex Andean societies, and signifying that the region served as a locus for early Hg extraction. The earliest mining targeted cinnabar (HgS) for the production of vermillion. Pre-Colonial Hg burdens peak ca. 500 BC and ca. 1450 AD, corresponding to the heights of the Chavín and Inca states, respectively. During the Inca, Colonial, and industrial intervals, Hg pollution became regional, as evidenced by a third lake record approximately 225 km distant from Huancavelica. Measurements of sediment-Hg speciation reveal that cinnabar dust was initially the dominant Hg species deposited, and significant increases in deposition were limited to the local environment. After conquest by the Inca (ca. 1450 AD), smelting was adopted at the mine and Hg pollution became more widely circulated, with the deposition of matrix-bound phases of Hg predominating over cinnabar dust. Our results demonstrate the existence of a major Hg mining industry at Huancavelica spanning the past 3,500 years, and place recent Hg enrichment in the Andes in a broader historical context.

Inertial deposition of aerosols in bifurcating models during steady expiratory flow

The deposition of respiratory aerosols during the expiratory phase of breathing may be significant. However, only a limited number of studies have considered the effects of exhalation on aerosol deposition in bifurcating respiratory geometries. In this study, double bifurcation models of respiratory generations G3–G5 and G7–G9 were used to determine the deposition of aerosols in the size range of 1 – 7 μ m during steady exhalation. The geometries considered were based on standard and 30% constricted pediatric airway models. A previously tested CFD code was implemented to predict aerosol deposition under laminar flow conditions. Results indicated that deposition in bifurcating airways during expiration was a function of the Stokes number, which represents particle inertia, and the Dean number, which captures the strength of secondary flow conditions. For a Dean number of approximately 10, deposition was observed to decrease with increasing values of the Stokes number. Increasing the Dean number above approximately 100 resulted in a significant increase in deposition for constant Stokes number values. Existing algebraic correlations did not capture the effects of the Dean number on deposition during exhalation. As a result, novel correlations were proposed that predicted branch-averaged deposition efficiency as a function of both Stokes and Dean numbers. Implementation of these correlations into whole-lung models is suggested to improve the prediction of deposition during exhalation under laminar expiratory conditions in bifurcating airways.

Templated Growth of Carbon Nanotubes with Controlled Diameters Using Organic-Organometallic Block Copolymers with Tailored Block Lengths

Block copolymer thin films fabricated from polystyrene-polyferrocenylsilane (PS-b-PFS) block copolymers on silicon substrates were used as precursors of well-ordered, nanosized growth catalysts for carbon nanotubes (CNTs). The size of the catalytic domains was tuned by changing the molecular weight of the block copolymer, enabling control of the diameter of the CNTs grown from these substrates. CNT growth on catalytic substrates with larger organometallic domain sizes, using acetylene as a carbon source, resulted in enhanced amounts of CNT deposition compared to smaller PFS domains, which exhibited low catalytic activity. The inner and outer diameters of the multi-walled CNTs obtained were typically 8 and 16 nm, respectively, and were not influenced by the catalytic domain sizes. Various annealing strategies in inert or in hydrogen atmosphere were investigated. The use acetylene with an additional hydrogen flow as gas feed resulted in a significant increase in deposition on all PS-b-PFS decorated substrates. Under these conditions, the CNT diameters could be controlled by the catalyst domain sizes, resulting in decreasing diameters with decreasing domain sizes. Multiwalled CNTs with inner and outer diameters of 4 and 7 nm, respectively, and a narrow diameter distribution were obtained.

Deposition of Aerosolized Particles in the Maxillary Sinuses before and after Endoscopic Sinus Surgery

Recent studies suggest that topical therapy is beneficial in many conditions underlying chronic sinusitis. Current literature has documented low aerosolized particle deposition efficiency into the paranasal sinuses. Mathematical modeling suggests that three factors influence the deposition efficiency: particle size, pressure gradient, and size of the sinus ostium. Ostium size is the most dominant factor. Therefore, we sought to determine if maxillary antrostomy and ethmoidectomy would increase the deposition efficiency. Five cadavers underwent pre- and postoperative scintigraphy after administration of aerosolized Tc-99M. Images were obtained with a gamma-camera and regions of interest (ROIs) were drawn around the maxillary sinuses. Counts per minute in the pre- and postoperative ROIs were then compared using the paired t-test. Results indicated a significant increase in deposition of radioactivity in the maxillary sinuses in the postoperative state (p < 0.01). Topical therapy for chronic sinusitis may be more feasible in the postoperative population.

CRITICAL LOADS FOR INORGANIC NITROGEN DEPOSITION IN THE COLORADO FRONT RANGE, USA

We suggest an empirical approach for determining critical loads for inorganic nitrogen (N) deposition in wetfall to the central Rocky Mountains (USA). We define “critical loads” as a deposition amount above which natural resources can be negatively affected. The arithmetic average from 1992 to 1996 of annual inorganic N deposition in wetfall at the eight National Acid-Deposition Program (NADP) sites located at elevations >2500 m in the central Rocky Mountains ranged from 2.5 to 3.5 kg·ha−1·yr−1. In contrast, inorganic N deposition was <2.5 kg·ha−1·yr−1 at all 23 NADP sites below 2500 m in elevation. At the Niwot Ridge NADP site in the Colorado Front Range, a simple linear regression of inorganic N in wetfall with time shows a significant increase in deposition of inorganic N in wetfall at the rate of 0.32 kg·ha−1·yr−1 (r2 = 0.62; P < 0.001, n = 13). In turn, the increasing amount of inorganic N in wetfall is causing episodic acidification in headwater catchments of the Green Lakes Valley in the Colorado Front Range, with acid-neutralizing capacity (ANC) values below 0 μmolc/L in surface waters during snowmelt runoff at 9-ha and 42-ha sampling sites. At present rates of ANC decrease, we can expect the 9-ha and 42-ha sites to become chronically acidified within the next decade and the 220-ha basin of Green Lake 4 to become episodically acidified. A synoptic survey in 1995 of 91 high-elevation lakes in the central Rocky Mountains suggests that water quality is being affected by inorganic N in wetfall throughout the region. Federal land managers are required to “err on the side of protection” when assessing the amount of deposition that will alter ecosystem processes. However, given the political and economic ramifications of policy decisions, land managers are aware of the need to provide a scientific basis for these decisions and to balance conflicting needs. To achieve this balance and to allow for natural-resource protection, we make a conservative recommendation that critical loads of inorganic N in wetfall to Class 1 areas in the central Rocky Mountains be set at 4 kg·ha−1·yr−1. Target loads may be set at lower levels of inorganic N deposition in wetfall to allow a margin of safety to protect extremely sensitive natural resources.

RECIRCULATING FLOW IN AN EXPANDING ALVEOLAR MODEL: EXPERIMENTAL EVIDENCE OF FLOW-INDUCED MIXING OF AEROSOLS IN THE PULMONARY ACINUS

Mixing processes of aerosol particles in the pulmonary acinus by rhythmic expansion of alveolar walls have recently been simulated within a realistic geometric model of the alveolar duct (Tsuda et al., 1995). We studied the velocity fields in an expanding large-scaled silicone copy of this alveolar model applying particle-image-velocimetry. Without wall expansion the flow fields are characterized by a large recirculation region within the alveolar sac and a separation streamline separating this region from the duct flow. With wall expansion, the topology of the flow entirely changed. A separation streamline at the alveolar opening disappeared. There was convective flow exchange between duct and alveolus. Large recirculation flows were often observed in the expanding alveolus, indicating the occurrence of stagnation saddle point in the alveolar flow field. Such singularity point is characteristic for the occurrence of chaotic flow mixing, which in turn leads to significant increase in deposition of fine aerosols in the pulmonary acinus.

Screening and selection of adjuvants for the spray application of entomopathogenic nematodes against a foliar pest

The effects of adding a number of adjuvants to sprays containing infective juveniles (IJS) of Heterorhabditis n.sp. and Steinernema sp. (M87:45) was examined. The adjuvants were not directly toxic to IJS of either nematode species or to larvae of the diamondback moth, Plutella xylostella. However, infectivity of the IJS to larvae of the wax-moth, Galleria mellonella, in terms of mortality and intensity of infection, was affected by the addition of the adjuvants, compared with IJS in water alone. Deposition studies showed that the proportion of droplets carrying IJS was not affected by the addition of the adjuvants following application with spinning disc sprayers (Micron Ulva + and Micron Herbaflex). However, additio of the adjuvants resulted in a significant increase in deposition, in terms of the mean numbers of IJS per cm 2. This was noted following application with both sprayers and for both nematode species. The spray spectra produced by either sprayer was generally not affected much by the addition of any of the adjuvants to the spray solutions.