Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P50583 (asymmetrical)
 12,197 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

A numerical model describing the local interactions between convection and diffusion in the first 11 generations (0 to 10) of the human bronchial tree is presented. The model, based on a Monte Carlo procedure, is used to investigate the effects of four velocity profiles: (i) parabolic, (ii) asymmetrical, (iii) asymmetrical with swirling and (iv) flat. Behavior was investigated for three diffusivities: (i) 0.75 cm2/s (He/air), (ii) 0.25 cm2/s (N2/O2) and (iii) 0.1 cm2/s (SF6/air) on the convection-diffusion interaction. The results of these simulations showed that 'Taylor dispersion' is an important effect, with respect to tracer segregation, and that it is of major significance only in the largest airways. By generation 10, molecular diffusion begins to dominate over Taylor dispersion. It was also found that use of a parabolic velocity profile, or application of the Gill-Sburamanian dispersion theory seriously overestimates axial dispersion. On the other hand, the use of a flat velocity profile underestimates dispersion.
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PMID:A Monte Carlo simulation of convective dispersion in the large airways. 49 49

We performed single breath washouts in 14 dogs and 4 pigs using a gas mixture containing 5% helium (He) and 5% sulphur hexafluoride (SF6) with, and without, an end inspiratory breathhold. In dogs, the slope of the alveolar plateau was steeper for SF6 than for He, the difference decreasing after 20 sec of breathholding. In contrast, in pigs there was no difference between the two slopes although both were steeper than in dogs. Following a 15-sec breathhold, both slopes decreased, that of the He plateau becoming significantly flatter than that for SF6. Furthermore, the expirate became relatively SF6 enriched. The results indicate that in pigs the mechanism responsible for the sloping alveolar plateau is not diffusion dependent, and hence cannot be due to 'stratification'. Neither do the results support diffusive interaction within an asymmetrical acinus as a basis for the slope. Our findings suggest that the latter is due to sequential emptying of relatively large units subtended by a branch point in which gas transport is entirely convective.
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PMID:Gas mixing in the lungs of dogs and pigs. 710 Jun 91

Particle penetration into lung airways during normal respiration is affected by the exchange of inspired air and residual gas. In this study, particle penetration during the inspiratory phase was investigated using gamma-tagged monodisperse particles (0.70, 0.90, 0.96, and 1.44 microns) suspended in various carrier gases having a wide range of kinematic viscosity. A 40-mL bolus of tagged aerosol was drawn into excised human and dog lungs at the end of a tidal breath, followed by a long breathhold to allow for complete particle deposition by sedimentation. The lungs were then fixed, sectioned, and autoradiographed to determine tidal front locations. In human lungs, particles suspended in He-O2 penetrated deeper than particles suspended in air; particles penetrated least in SF6-O2. Dog lungs, which have more asymmetrical airway branching patterns than human lungs, had no significant particle penetration differences associated with carrier gas composition. It is concluded that particle penetration during the inspiratory phase is dependent on factors that determine flow profile development, such as branching pattern and the Reynolds number of the carrier gas. The bolus front at the end of an air inspiration extended into about 10% of human lung airways of 1 mm diameter, and into about 0.1% of 0.5-mm airways. It is concluded that rapid particle penetration to 1-mm airways during high-frequency oscillatory ventilation of lung casts is due to cumulative axial core transport during multiple breathing cycles. Similarly, the dispersion of an aerosol bolus from large airways to small airways during in vivo breathholding studies appears to be due to oscillatory flow created by the heartbeat.
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PMID:Effect of lung airway branching pattern and gas composition on particle deposition in bronchial airways: III. Experimental studies with radioactively tagged aerosol in human and canine lungs. 839 32