Determination of regional lung air volume distribution at mid-tidal breathing from computed tomography: A retrospective study of normal variability and reproducibility

© 2014 Fleming et al.; licensee BioMed Central Ltd. Background: Determination of regional lung air volume has several clinical applications. This study investigates the use of mid-tidal breathing CT scans to provide regional lung volume data.Methods: Low resolution CT scans of the thorax were obtained during tidal breathing in 11 healthy control male subjects, each on two separate occasions. A 3D map of air volume was derived, and total lung volume calculated. The regional distribution of air volume from centre to periphery of the lung was analysed using a radial transform and also using one dimensional profiles in three orthogonal directions.Results: The total air volumes for the right and left lungs were 1035 +/- 280 ml and 864 +/- 315 ml, respectively (mean and SD). The corresponding fractional air volume concentrations (FAVC) were 0.680 +/- 0.044 and 0.658 +/- 0.062. All differences between the right and left lung were highly significant (p < 0.0001). The coefficients of variation of repeated measurement of right and left lung air volumes and FAVC were 6.5% and 6.9% and 2.5% and 3.6%, respectively. FAVC correlated significantly with lung space volume (r = 0.78) (p < 0.005). FAVC increased from the centre towards the periphery of the lung. Central to peripheral ratios were significantly higher for the right (0.100 +/- 0.007 SD) than the left (0.089 +/- 0.013 SD) (p < 0.0001).Conclusion: A technique for measuring the distribution of air volume in the lung at mid-tidal breathing is described. Mean values and reproducibility are described for healthy male control subjects. Fractional air volume concentration is shown to increase with lung size.Air Liquid

An in silico analysis of oxygen uptake of a mild COPD patient during rest and exercise using a portable oxygen concentrator

Ira Katz,1,2 Marine Pichelin,1 Spyridon Montesantos,1 Min-Yeong Kang,3 Bernard Sapoval,3,4 Kaixian Zhu,5 Charles-Philippe Thevenin,5 Robert McCoy,6 Andrew R Martin,7 Georges Caillibotte1 1Medical R&amp;D, Air Liquide Sant&eacute; International, Centre de Recherche Paris-Saclay, Les Loges-en-Josas, France; 2Department of Mechanical Engineering, Lafayette College, Easton, PA, USA; 3Physique de la Mati&egrave;re Condens&eacute;e, CNRS, Ecole Polytechnique, Palaiseau, 4Centre de Math&eacute;matiques et de leurs Applications, CNRS, UniverSud, Cachan, 5Centre Explor!, Air Liquide Healthcare, Gentilly, France; 6Valley Inspired Products, Inc, Apple Valley, MN, USA; 7Department of Mechanical Engineering, University of Alberta, Edmonton, AB, Canada Abstract: Oxygen treatment based on intermittent-flow devices with pulse delivery modes available from portable oxygen concentrators (POCs) depends on the characteristics of the delivered pulse such as volume, pulse width (the time of the pulse to be delivered), and pulse delay (the time for the pulse to be initiated from the start of inhalation) as well as a patient&rsquo;s breathing characteristics, disease state, and respiratory morphology. This article presents a physiological-based analysis of the performance, in terms of blood oxygenation, of a commercial POC at different settings using an in silico model of a COPD patient at rest and during exercise. The analysis encompasses experimental measurements of pulse volume, width, and time delay of the POC at three different settings and two breathing rates related to rest and exercise. These experimental data of device performance are inputs to a physiological-based model of oxygen uptake that takes into account the real dynamic nature of gas exchange to illustrate how device- and patient-specific factors can affect patient oxygenation. This type of physiological analysis that considers the true effectiveness of oxygen transfer to the blood, as opposed to delivery to the nose (or mouth), can be instructive in applying therapies and designing new devices. Keywords: efficiency, respiratory physiology, respiratory disease, pulsed deliver

Using helium-oxygen to improve regional deposition of inhaled particles: mechanical principles

Background: Helium-oxygen has been used for decades as a respiratory therapy conjointly with aerosols. It has also been shown under some conditions to be a means to provide more peripheral, deeper, particle deposition for inhalation therapies. Furthermore, we can also consider deposition along parallel paths that are quite different, especially in a heterogeneous pathological lung. It is in this context that it is hypothesized that helium-oxygen can improve regional deposition, leading to more homogeneous deposition by increasing deposition in ventilation-deficient lung regions.Methods: Analytical models of inertial impaction, sedimentation, and diffusion are examined to illustrate the importance of gas property values on deposition distribution through both fluid mechanics– and particle mechanics–based mechanisms. Also considered are in vitro results from a bench model for a heterogeneously obstructed lung. In vivo results from three-dimensional (3D) imaging techniques provide visual examples of changes in particle deposition patterns in asthmatics that are further analyzed using computational fluid dynamics (CFD).Results and Conclusions: Based on analytical modeling, it is shown that deeper particle deposition is expected when breathing helium-oxygen, as compared with breathing air. A bench model has shown that more homogeneous ventilation distribution is possible breathing helium-oxygen in the presence of heterogeneous obstructions representative of central airway obstructions. 3D imaging of asthmatics has confirmed that aerosol delivery with a helium-oxygen carrier gas results in deeper and more homogeneous deposition distributions. CFD results are consistent with the in vivo imaging and suggest that the mechanics of gas particle interaction are the source of the differences seen in deposition patterns. However, intersubject variability in response to breathing helium-oxygen is expected, and an example of a nonresponder is shown where regional deposition is not significantly changed.<br/

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

Modulation of the refractive properties of 1D and 2D photonic crystal polycrystalline silicon-based membranes in the MIR frequency range

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