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At least 685 records · Page 38Linked to original sources
PubMed1985

Pores in avian eggshells: gas conductance, gas exchange and embryonic growth rate.

The number of pores (N) in eggshells of birds were counted in 161 species ranging in egg mass (W) from 0.9 to 500 g. In addition the water vapor conductance of the shell (G) mg X (d X Torr)-1, the water loss in the nest (M) mg X d-1, the incubation duration (I) d, and the shell thickness or pore length (L) micron are listed for each species when available. Allometric equations for all variables are given when regressed on egg mass. When log G is regressed on log N the slope is essentially 1.0 indicating that the G X N-1 for average pores in bird eggshells is 1.5 micrograms H2O X (d X Torr)-1 regardless of egg mass or incubation duration. According to Fick's law of diffusion such pores have a cross-sectional area to pore length ratio of 0.67 micron 2 X micron-1. Further analysis show that N, G, M, and the rate of oxygen consumption at the pre-internal pipping stage, are all directly proportional to the absolute mean growth rate of embryos (defined as 0.67 [W/I], g X d-1). Thus, single pores of typical eggshells not only have a similar conductance G X N-1, but also the metabolic rate and rate of water loss are matched to the pore conductance so that O2, CO2 fluxes per pore at the pre-internal pipping stage and water vapor flux per pore are similar among species, namely 68, 49 and 50 microliters X d-1, respectively. The partial pressure differences across the shell at the same stage are 42, 40 and 27 Torr, respectively. Ecological as well as taxonomical variation may alter some of the relationships predicted for the 'typical' egg in order to conserve a typical overall diffusive water loss.

Animals↗
PubMed1998

Sigmoidal compression rate-dependence of inert gas narcotic potency in rats: implication for lipid vs. protein theories of inert gas action in the central nervous system.

Inert gases at raised pressure exert anaesthetic effects. It is assumed that anaesthesia by the inert gases is fundamentally similar to anaesthesia produced by general anaesthetics. However, do general anaesthetics bind directly to proteins or influence activity by indirectly perturbing membrane lipids still remains a major question. Although the pressure required to achieve anaesthesia with inert gases has been suggested to exert potentially some pressure antagonism per se, this has not been studied yet to our knowledge. We investigated this possibility using nitrogen, argon, and nitrous oxide. Whatever the narcotic agent used, our results showed that the pressure of narcotic required to induce anaesthetic effects increased, as compression rate increased, in a sigmoid fashion rather than in a linear fashion. Evidence for sigmoïdal responses vs. linear responses depended of the narcotic potency of the anaesthetic agent used (nitrogen: r2=0.973 vs. r2=0.941; argon: r2=0. 971 vs. r2=0.866; nitrous oxide: r2=0.995 vs. r2=0.879). Since a linear antagonism is predicted by lipid theories, we think it likely that these findings indicate that inert gases bind to a modulatory site of a protein receptor and act as allosteric modulators. Since other workers provided evidence for binding processes using volatile anaesthetics, the present findings could indicate that all classes of general anaesthetics, including inert gases, could act by binding directly to proteins rather than by dissolving in some lipids of the cellular membrane.

Anesthetics, Inhalation↗
PubMed2001

Simultaneous administration of glucose and hyperoxic gas achieves greater improvement in tumor oxygenation than hyperoxic gas alone.

PURPOSE: To test the feasibility of hyperglycemic reduction of oxygen consumption combined with oxygen breathing (O(2)), to improve tumor oxygenation. METHODS AND MATERIALS: Fischer-344 rats bearing 1 cm R3230Ac flank tumors were anesthetized with Nembutal. Mean arterial pressure, heart rate, tumor blood flow ([TBF], laser Doppler flowmetry), pH, and pO(2) were measured before, during, and after glucose (1 or 4 g/kg) and/or O(2). RESULTS: Mean arterial pressure and heart rate were unaffected by treatment. Glucose at 1 g/kg yielded maximum blood glucose of 400 mg/dL, no change in TBF, reduced tumor pH (0.17 unit), and 3 mm Hg pO(2) rise. Glucose at 4 g/kg yielded maximum blood glucose of 900 mg/dL, pH drop of 0.6 unit, no pO(2) change, and reduced TBF (31%). Oxygen tension increased by 5 mm Hg with O(2). Glucose (1 g/Kg) + O(2) yielded the largest change in pO(2) (27 mm Hg); this is highly significant relative to baseline or either treatment alone. The effect was positively correlated with baseline pO(2), but 6 of 7 experiments with baseline pO(2) < 10 mm Hg rose above 10 mm Hg after combined treatment. CONCLUSION: We demonstrated the feasibility of combining hyperglycemia with O(2) to improve tumor oxygenation. However, some cell lines are not susceptible to the Crabtree effect, and the magnitude is dependent on baseline pO(2). Additional or alternative manipulations may be necessary to achieve more uniform improvement in pO(2).

Animals↗
PubMed2006

A new approach to determining gas-particle reaction probabilities and application to the heterogeneous reaction of deliquesced sodium chloride particles with gas-phase hydroxyl radicals.

The reaction kinetics for gaseous hydroxyl radicals (OH) with deliquesced sodium chloride particles (NaCl(aq)) were investigated using a novel experimental approach. The technique utilizes the exposure of substrate-deposited aerosol particles to reactive gases followed by chemical analysis of the particles using computer-controlled scanning electron microscopy with energy-dispersive analysis of X-rays (CCSEM/EDX) capability. Experiments were performed at room temperature and atmospheric pressure with deliquesced NaCl particles in the micron size range at 70-80% RH and with OH concentrations in the range of 1 to 7 x 10(9) cm(-3). The apparent, pseudo first-order rate constant for the reaction was determined from measurements of changes in the chloride concentration of individual particles upon reaction with OH as a function of the particle loading on the substrate. Quantitative treatment of the data using a model that incorporates both diffusion and reaction kinetics yields a lower limit to the net reaction probability of gamma(net) > or = 0.1, with an overall uncertainty of a factor of 2.

Journal Article↗