Changes in the spatial distribution of perfusion during acute lung injury and their impact on gas exchange are poorly understood. We tested whether endotoxemia caused topographical differences in perfusion and whether these differences caused meaningful changes in regional ventilation-to-perfusion ratios and gas exchange. Regional ventilation and perfusion were measured in anesthetized, mechanically ventilated pigs in the prone position before and during endotoxemia with the use of aerosolized and intravenous fluorescent microspheres. On average, relative perfusion halved in ventral and cranial lung regions, doubled in caudal lung regions, and increased 1.5-fold in dorsal lung regions during endotoxemia. In contrast, there were no topographical differences in perfusion before endotoxemia and no topographical differences in ventilation at any time point. Consequently, endotoxemia increased regional ventilation-to-perfusion ratios in the caudal-to-cranial and dorsal-to-ventral directions, resulting in end-capillary PO2 values that were significantly lower in dorsal-caudal than ventral-cranial regions. We conclude that there are topographical differences in the pulmonary vascular response to endotoxin that may have important consequences for gas exchange in acute lung injury. 相似文献
The heterogeneity of pulmonary blood flow is not adequately described by gravitational forces alone. We investigated the flow distributions predicted by two fractally branching vascular models to determine how well such networks could explain the observed heterogeneity. The distribution of flow was modeled with a dichotomously branching tree in which the fraction of blood flow from the parent to the daughter branches was gamma and 1-gamma repeatedly at each generation. In one model gamma was held constant throughout the network, and in the other model gamma varied about a mean of 0.5 with a standard deviation of sigma. Both gamma and sigma were optimized in each model for the best fit to pulmonary blood flow data from experimental animals. The predicted relative dispersion of flow from the two model fractal networks produced an excellent fit to the observed data. These fractally branching models relate structure and function of the pulmonary vascular tree and provide a mechanism to describe the spatially correlated distribution of flow and the gravity-independent heterogeneity of blood flow. 相似文献
This review describes approaches to the analysis of fractal properties of physiological observations. Fractals are useful to describe the natural irregularity of physiological systems because their irregularity is not truly random and can be demonstrated to have spatial or temporal correlation. The concepts of fractal analysis are introduced from intuitive, visual, and mathematical perspectives. The regional heterogeneities of pulmonary and myocardial flows are discussed as applications of spatial fractal analysis, and methods for estimating a fractal dimension from physiological data are presented. Although the methods used for fractal analyses of physiological data are still under development and will require additional validation, they appear to have great potential for the study of physiology at scales of resolution ranging from the microcirculation to the intact organism. 相似文献
Molecular systematists need increased access to nuclear genes. Highly
conserved, low copy number protein-encoding nuclear genes have attractive
features for phylogenetic inference but have heretofore been applied mostly
to very ancient divergences. By virtue of their synonymous substitutions,
such genes should contain a wealth of information about lower-level
taxonomic relationships as well, with the advantage that amino acid
conservatism makes both alignment and primer definition straightforward. We
tested this postulate for the elongation factor-1 alpha (EF-1 alpha) gene
in the noctuid moth subfamily Heliothinae, which has probably diversified
since the middle Tertiary. We sequenced 1,240 bp in 18 taxa representing
heliothine groupings strongly supported by previous morphological and
allozyme studies. The single most parsimonious gene tree and the
neighbor-joining tree for all nucleotides show almost complete concordance
with the morphological tree. Homoplasy and pairwise divergence levels are
low, transition/transversion ratios are high, and phylogenetic information
is spread evenly across gene regions. The EF-1 alpha gene and presumably
other highly conserved genes hold much promise for phylogenetics of
Tertiary age eukaryote groups.
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Activation of adenylate cyclase in isolated rat liver plasma membranes by cholera toxin was demonstrated. The activation requires the presence of NAD+ and ATP and is irreversible. 相似文献
Cultured chick embryo fibroblasts derived from skin and skeletal muscle exhibit hyaluronidase activity both associated with the cell layer and secreted into the medium. Although both forms of the enzyme have a number of similar characteristics (R.W. Orkin and B.P. Toole, 1980, J. Biol. CHem. 255), they differ in thermal stability at neutral pH and in behavior on ion-exchange chromatography. Both forms of the enzyme are equally stable at acidic pH for long intervals, but the cell-associated hyaluronidase is significantly less stable than the secreted froms at neutral pH and at temperatures more than or equal to 30 degrees C. Neither the presence of proteases nor inhibitors of hyaluronidase appear to be involved in the cell-asspcoated enzyme. Chromatography of the two forms of hyaluronidase on carboxymethyl cellulose reveals that most (60-90 percent) of the secreted form of the enzyme elutes at a lower ionic strength than the cell- associated enzyme. Treatment of the secreted form of hyaluronidase with neuraminidase shifts its elution profile on carboxymethyl cellulose toward that of the cell-associated form, and also decreases its thermal stability at neutral pH. In contrast, treatment of the secreted form of hyaluronidase with alkaline phosphatase has no detectable effect. These data suggest that the secreted hyaluronidase differs from the cellular form in possessing additional sialic acid residues which endow the former with increased stability in the extracellular milieu. 相似文献
Introduction.Cheilolejeunea morganii Bever. & Glenny, a new species of Cheilolejeunea from a lowland forest habitat in eastern Taranaki in the North Island of New Zealand, is described and illustrated.
Methods. DNA sequences were extracted from recently collected material at two locations and compared with those for species in a published phylogeny of the genus to establish the position of C. morganii. Photographic images were obtained of key features of the species for the preparation of illustrations for publication.
Key results.Cheilolejeunea morganii does not match any species described for New Zealand or Australia. The sequencing results indicate its position in the phylogeny is close to Section Paroicae. A key to the New Zealand species of Cheilolejeunea is provided.
Conclusions. In the Australasian flora, C. morganii is distinguished from other species by its combination of monoicy, pycnolejeuneoid gynoecial innovations, lobule length less than 50% lobe length and a multicellular second lobule tooth with 3–4 cells uniseriate. A case is presented for the recognition of the species as a New Zealand endemic. 相似文献
Seven fluorescent microsphere colors can be used in a single experiment to estimate regional blood flow without correcting for spillover of emitted fluorescence. To extend the method to 13 colors, we compared the accuracy of three methods for spillover correction. Fixed wavelength intensities were corrected by matrix inversion, and synchronous scan spectra were corrected by least squares fit of an overdetermined system of linear equations and by least squares fit of a sum of Gaussian and Lorentzian functions. Correction methods were validated in pigs and sheep by simultaneous injections of radioactive microspheres and fluorescent microspheres of 7, 10, and 13 different colors. We induced extreme changes in flow to create regions with low fluorescent signals bound on either side by high fluorescent signals. Blood flow was determined by radioactivity and by fluorescence using both fixed excitation and emission wavelength pairs and synchronous scanning and then corrected for spillover. Correlation between fluorescent intensity and radioactivity were excellent for all three correction methods [R2 = 0.98 +/- 0.02 (mean +/- SD)]. Low-flow regions requiring large spillover correction had systematic errors for some color combinations in all methods. We conclude that for 13 fluorescent colors spillover error can be minimized so that all three correction methods provide accurate estimates of regional blood flow. 相似文献