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Viewpoint response to unresolved mysteries.
J Appl Physiol 2012 Dec; 113(12):1948-1949
To the editor: Inconsistences between the studies of Hajari and Smaldone (3) result from differences in the interpretation of findings based on particle deposition and MRI measurements. The aerosol deposition analysis depends on the settling velocity of an even distribution of particles in the periphery of the lungs during a 6-s breath-hold to estimate Lm. Although this technique is unique, questions remain: 1) K/Lm increased from approximately 0.25, during lung inflation, to approximately 0.6 then stayed constant during lung deflation before rising sharply to approximately 0.9 at low lung volumes. If the lung were reinflated, K/Lm would presumably decrease abruptly, while total lung volume remained nearly unchanged. One explanation is that the airways contribute significantly to particle deposition in the lung during lung inflation. 2) In another study, when Lm of the air spaces in the lung's periphery was determined using a laser light scattering technique (1), Lm increased as lung volume increased and was larger during lung inflation than deflation. 3) Gas trapping, resulting from liquid film formation, occurs normally in excised lungs (2). The films impede particle diffusion much more than respiratory gases (4). Methods to reduce gas trapping were reported (4), but it is doubtful that film formation was completely eliminated. Another interpretation of the aerosol results is that alterations in deposition resulting from the formation and movement of liquid barriers in airways could account for the increase in K/Lm during lung inflation. As a result, aerosol deposition may not exclusively reflect changes in the geometry of peripheral lung structures.
Aerosols; Particulates; Lung; Lung-function; Breathing; Respiration; Respiratory-gases; Airway-obstruction; Physiological-factors; Physiology
Issue of Publication
Journal of Applied Physiology
Page last reviewed: September 2, 2020
Content source: National Institute for Occupational Safety and Health Education and Information Division