Does resistive loading decrease diaphragmatic contractility before task failure?

While sustaining a load that leads to taskfailure, it is unclear whether diaphragmatic fatigue developsprogressively or occurs only at task failure. We hypothesized thatincremental loading produces a progressive decrease in diaphragmaticcontractility ever before task failure. Ten subjectsgenerated 60% of maximal transdiaphragmatic pressure(Pdi_max) for 2 min, 4 min, anduntil task failure. Before loading, 20 min after each period ofloading, and ~20 h after the last period of loading,Pdi_max, nonpotentiated andpotentiated Pdi twitch pressure(Pdi_tw), and the pattern of respiratory muscle recruitment during aCO₂ challenge were recorded. Sensation of inspiratory effort at the 4th min of the task-failure protocol was greater than at the same time in the preceding 4-min protocol. Surprisingly, potentiatedPdi_tw andPdi_max were reduced after 2 min ofloading and decreased further after 4 min of loading and after taskfailure; nonpotentiated Pdi_tw wasreduced after 4 min of loading and after task failure. The gastricpressure contribution to tidal breathing during aCO₂ challenge decreased progressively in relation to duration of the preceding loading period,whereas expiratory muscle recruitment progressively increased. A restperiod of ~20 h after task failure was not sufficient to normalizethese alterations in respiratory muscle recruitment or fatigue-inducedchanges in diaphragmatic contractility. In conclusion, while sustaininga mechanical load, the diaphragm progressively fatigued, ever beforetask failure, and when challenged the rib cage-to-diaphragmaticcontribution to tidal breathing and recruitment of the expiratorymuscles increased pari passu with duration of the preceding loading.

     

Development of magnetic biosorbents for metal uptake

Two types of magnetic biosorbent were prepared by novel protocols from epichlorhydrin-cross-linked Saccharomyces cerevisiae cell walls and their biosorption characteristics were compared to those of non-magnetic cell walls. The magnetic biosorbents I and II were capable of binding Cu maximally to 225 and 50 mmol/g, Cd to 90 and 25 mmol/g and Ag + to 80 and 45 mmol/g respectively. These values compare with 400, 125 and 75 mmol/g, respec-tively, for non-magnetic cell walls.     

Light-scattering and specific refractive increment behavior of amylose and dextran in methyl sulfoxide-water

Light-scattering measurements on polysaccharides in methyl sulfoxide or methyl sulfoxide-water are most reliable when made on a dialyzed solution-solvent system and when proper technique is used to remove the “micro gel” that seems unavoidably present when dried polysaccharide is dissolved in solvent. Discrepancies in published molecular weight-intrinsic viscosity relationships for amylose in methyl sulfoxide appear to be caused in part by differences the preparation and treatment of samples and possibly by differences in botanical source. The specific refractive increment of dextran is not a linear function of solvent composition in methyl sulfoxide-water. Measurements at osmotic equilibrium indicate that, over a moderate range of composition in methyl sulfoxide-water, dextran preferentially associates with about 2.5 molecules of water per glucopyranosyl residue of the polymer. Effects of long-term storage, sample treatment, and botanical source upon the specific rotation of amylose are examined.     

In situ imaging of microorganisms in geologic material.

In order to fully delineate the interactions of microorganisms with geological substrates, unequivocal identification of intact microbial cells within geologic samples is required without the disruption of either the rock texture or the relationship of the microorganisms to the mineral fabric. To achieve this objective we developed a protocol that enables the visualization of intact microbial cells in petrographic thin sections, avoids detaching the cells from their host mineral surfaces and avoids microbial contamination during the lapidary process. Propidium iodide and POPO-3, nucleic acid stains that specifically target double-stranded DNA and RNA were utilized for in situ visualization of cells in surface and subsurface basalts from northeastern Idaho. Additionally, examination of samples incubated with acetic acid-UL-14C via phosphor imagining facilitated the in situ visualization of 14C labeled biomass. Biomass observed was low (<10(7) cells/g). These observations indicate that the microbial distribution in these rocks exhibits a high degree of spatial heterogeneity at the sub-centimeter scale.