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81.
- 1. 1. The ventilatory and pulmonary gas exchange responses during moderate exercise can be appropriately modelled with first-order dynamics.
- 2. 2. A delay term, reflecting tissue-to-lung transit time, is needed for accurate characterization, however.
- 3. 3. The O2 uptake time constant ( reflects the enzymatically controlled tissue O2 utilization.
- 4. 4. is appreciably longer than , consequent to the tissue CO2 capacitance.
- 5. 5. As typically longer than , transient errors in alveolar and arterial blood gas tensions are predicted: small for PCO2 but much larger for PO2.
- 6. 6. At work rates above the lactate threshold, a slow and delayed component of V̇O2 induces an additional V̇ component (“excess” V̇O2), leading to more rapid fatigue.
- 7. 7. The ventilatory compensation for the metabolic acidemia at these work rates is slow, with compensation being poor for rapid-incremental exercise.
- 8. 8. A justifiable control model of the coupling of ventilation to metabolism must cohere with these demonstrable physiological characteristics.
Keywords: Ventilation; pulmonary gas exchange; excess V̇O2; compensatory hyperpnea; model order 相似文献
82.
Abdullah Jaffer Brian Harvey Vivienne Ann Russell Machteld Elizabeth Carstens Anna Susanna de Villiers Joshua Joachim Fransua Taljaard 《Neurochemical research》1993,18(10):1057-1061
Chronic treatment of rats with lithium chloride was examined in order to determine its effect on hypothalamic monoamine and metabolite content, basal thyrotropin (TSH) secretion and thyroid function. The hypothalamic concentrations of noradrenaline (NA), dopamine (DA) and its metabolites, dihydroxyphenylacetic acid. (DOPAC) and homovanillic acid (HVA) in the lithium treated rats remained unaltered when compared to control levels. NA turnover and the NA metabolite, 3-methoxy-4-hydroxyphenylglycol (total MHPG), were significantly lower (p<0.01), whereas both serotonin (5-HT) and its metabolite, 5-hydroxyindole-3-acetic acid (5-HIAA), were significantly higher (p<0.01 and p<0.02, respectively) in the lithium treated rat hypothalami than in controls. Chronic lithium treatment significantly elevated basal TSH levels (p<0.05). This effect was antagonized by methylp-hydroxybenzoate (methylparaben, p<0.01), which did not itself affect basal TSH levels. Free serum T3 and T4 levels were not significantly affected by chronic lithium treatment, although T4 tended to be slightly lower than control levels. The monoamine changes observed in the hypothalamus of lithium treated rats did not appear to account for the elevated TSH levels observed in these rats since NA activity which is generally regarded as stimulatory was decreased and 5-HT which has an inhibitory effect on TSH secretion, was increased. The elevated TSH levels may have been due to a reduced negative feedback inhibition of TSH release by the mildly reduced circulating T4 levels caused by chronic lithium treatment. A further possibility is that the pituitary cGMP (and hence TSH) response to TRH may have been enhanced by chronic lithium treatment and methylparaben may have antagonized this effect. 相似文献
83.
Deletion analysis of the essentiality of penicillin-binding proteins 1A, 2B and 2X of Streptococcus pneumoniae 总被引:5,自引:0,他引:5
Christopher M. Kell Umender K. Sharma Christopher G. Dowson Christine Town Tanjore S. Balganesh Brian G. Spratt 《FEMS microbiology letters》1993,106(2):171-175
Abstract An internal fragment from each of the penicillinebinding protein (PBP) 1A, 2B and 2X genes of Streptococcus pneumoniae , which included the region encoding the active-site serine residue, was replaced by a fragment encoding spectinomycin resistance. The resulting constructs were tested for their ability to transform S. pneumoniae strain R6 to spectinomycin resistance. Spectinomycin-resistant transformants could not be obtained using either the inactivated PBP 2X or 2B genes, suggesting that deletion of either of these genes was a lethal event, but they were readily obtained using the inactivated PBP 1A gene. Analysis using the polymerase chain reaction confirmed that the latter transformants had replaced their chromosomal copy of the PBP 1A gene with the inactivated copy of the gene. Deletion of the PBP 1A gene was therefore tolerated under laboratory conditions and appeared to have little effect on growth or susceptibility to benzylpenicillin. 相似文献
84.
Synopsis Four species of nototheniid fish were sampled from below the sea ice near Cape Armitage, McMurdo Sound:Pagothenia borchgrevinki from just below the ice 1.5 km offshore,Trematomus bernacchii, Trematomus hansoni andTrematomus centronotus from off the bottom in about 20 m of water near the shore. Scale worms and isopods were conspicuous non-planktonic prey, and present in the three benthic fish species. The planktonic pteropod molluscLimacina helicina was numerically common in all four species of fish. The planktonic hyperiid amphipodHyperiella dilatata was also found in all fish species. WhereasP. borchgrevinki is planktivorous in accord with its pelagic habit, theTrematomus spp. clearly also feed on plankton from the water column.T. hansoni is particularly planktivorous, taking smaller copepods thanP. borchgrevinki. 相似文献
85.
Lawrence Cris W.; Little Pamela A.; Little Brian W.; Glushka John; van Halbeek Herman; Alhadeff Jack A. 《Glycobiology》1993,3(3):249-259
The N-glylycans have been removed by peptide-N-glycosidase F(PNGase F) from purified human non-secretory RNases derivedfrom kidney, liver and spleen. The spleen RNase was purifiedby two procedures, one of which did not include the usual acidtreatment step (0.25 M H2SO4, 45 min, 4C), to determine ifacid treatment alters the carbohydrate moieties. TheN-glycansof the RNases were fractionated by Bio-Gel P-4 chromatographyand analysed by 600 MHz 1H-NMR spectroscopy and electrospraymass spectrometry. All four non-secretory RNase preparationscontained the following structures: The relative amounts of the trisaccharide, pentasaccharide andhexasaccharide appeared to vary slightly in the different tissueRNases. The overall results indicate: (i) that acid treatmentduring purification does not alter the N-glycans of non-secretoryRNases; (ii) that the N-glycans from kidney, liver and spleennon-secretory RNases are very similar, if not identical, toone another, but different from the N-glycan structures reportedfor secretory RNase. N-glycans non-secretory RNases 相似文献
86.
87.
Julie A. Woods John A. Hadfield Alan T. McGown Brian W. Fox 《Bioorganic & medicinal chemistry》1993,1(5)
Bis(2-bromo-4,5-dimethoxyphenyl)sulfide (5) and bis(2-bromo-4,5-dimethoxyphenyl) selenide (7) have been shown to block cells in the G2/M phase of the cell cycle, whereas the debromo (4, 6) equivalents do not. The dibromoselenide (7) is cytotoxic to tumour cells in vitro and has been shown to increase the mitotic index of treated cells. These biological effects are consistent with disruption of the mitotic apparatus. This agent does not inhibit microtubule assembly in vitro, but does bind to tubulin. Molecular modelling of these structures indicates that their spatial and electronic structures may make an important contribution to the biological activity. 相似文献
88.
Brian W. Bowen Anne B. Meylan J. Perran Ross Colin J. Limpus George H. Balazs John C. Avise 《Evolution; international journal of organic evolution》1992,46(4):865-881
To address aspects of the evolution and natural history of green turtles, we assayed mitochondrial (mt) DNA genotypes from 226 specimens representing 15 major rookeries around the world. Phylogenetic analyses of these data revealed (1) a comparatively low level of mtDNA variability and a slow mtDNA evolutionary rate (relative to estimates for many other vertebrates); (2) a fundamental phylogenetic split distinguishing all green turtles in the Atlantic-Mediterranean from those in the Indian-Pacific Oceans; (3) no evidence for matrilineal distinctiveness of a commonly recognized taxonomic form in the East Pacific (the black turtle C.m. agassizi or C. agassizi); (4) in opposition to published hypotheses, a recent origin for the Ascension Island rookery, and its close genetic relationship to a geographically proximate rookery in Brazil; and (5) a geographic population substructure within each ocean basin (typically involving fixed or nearly fixed genotypic differences between nesting populations) that suggests a strong propensity for natal homing by females. Overall, the global matriarchal phylogeny of Chelonia mydas appears to have been shaped by both geography (ocean basin separations) and behavior (natal homing on regional or rookery-specific scales). The shallow evolutionary population structure within ocean basins likely results from demographic turnover (extinction and colonization) of rookeries over time frames that are short by evolutionary standards but long by ecological standards. 相似文献
89.
90.
Brian Mathew 《Curtis's Botanical Magazine》2003,20(4):250-251
Book reviewed in this article:
John Manning, Peter Goldblatt and Dee Snijman, The Color Encyclopedia of Cape Bulbs 相似文献
John Manning, Peter Goldblatt and Dee Snijman, The Color Encyclopedia of Cape Bulbs 相似文献