A model of the recruitment-derecruitment and volume of lung units in an excised lung as it is inflated-deflated between minimum and maximum lung volume.

The role of the recruitment-derecruitment of small structures in the lung (lung units) as the lung increases and decreases in volume has been debated. The objective of this study was to develop a model to estimate the change in the number and volume of open lung units as an excised lung is inflated-deflated between minimum and maximum lung volume. The model was formulated based on the observation that the compliance of the slowly changing quasi-static pressure-volume (P-V) curve of an excised rat lung can differ from the compliance of a faster changing small sinusoidal pressure volume perturbations superimposed on the curve. In those regions of the curve where differences in compliance occur, the lung tissue properties exhibit nonlinear characteristics, which cannot be linearized using "incremental" or "small signal" analysis. The model attributes the differences between the perturbation and quasi-static compliance to an additional nonlinear compliance term that results from the sequential opening and closing of lung units. Using this approach, it was possible to calculate the normalized average volume and the normalized number of open units as the lung is slowly inflated-deflated. Results indicate that the normalized average volume and the normalized number of open units are not linearly related to normalized lung volume, and at equal lung volumes the normalized number of open units is greater and the normalized average lung unit volume is smaller during lung deflation when compared to lung inflation. In summary, a model was developed to describe the recruitment-derecruitment process in excised lungs based on the differences between small signal perturbation compliance and quasi-static compliance. Values of normalized lung unit volume and the normalized number of open lung units were shown to be nonlinear functions of both transpulmonary pressure and normalized lung volume.

Development of an improved methodology to detect infectious airborne influenza virus using the NIOSH bioaerosol sampler.

A unique two-stage cyclone bioaerosol sampler has been developed at NIOSH that can separate aerosols into three size fractions. The ability of this sampler to collect infectious airborne viruses from a calm-air chamber loaded with influenza A virus was tested. The sampler's efficiency at collecting aerosolized viral particles from a calm-air chamber is essentially the same as that from the high performance SKC BioSampler that collects un-fractionated particles directly into a liquid media (2.4 × 10(4) total viral particles per liter of sampled air (TVP/L) versus 2.6 × 10(4) TVP/L, respectively, after 15 min) and the efficiency is relatively constant over collection times of 15, 30 and 60 min. Approximately 34% of the aerosolized infectious virus collected after 15 min with the NIOSH bioaerosol sampler remained infectious, and infectious virus was found in all three size fractions. After 60 min of sampling, the infectious virus/liter air found in the NIOSH bioaerosol sampler was 15% of that found in the SKC BioSampler. This preservation of infectivity by the NIOSH bioaerosol sampler was maintained even when the initial infectivity prior to aerosolization was as low as 0.06%. The utility of the NIOSH bioaerosol sampler was further extended by incorporating an enhanced infectivity detection methodology developed in our laboratory, the viral replication assay, which amplified the infectious virus making it more readily detectable.