Browsing by Author "Leiva, A"

Now showing 1 - 5 of 5
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    Breathing pattern and gas exchange at peak exercise in COPD patients with and without tidal flow limitation at rest
    (EUROPEAN RESPIRATORY SOC JOURNALS LTD, 2001) Diaz, O; Villafranca, C; Ghezzo, H; Borzone, G; Leiva, A; Milic Emili, J; Lisboa, C
    Expiratory flow limitation (FL) at rest is frequently present in chronic obstructive pulmonary disease (COPD) patients. It promotes dynamic hyperinflation with a consequent decrease in inspiratory capacity (IC), Since in COPD resting IC is strongly correlated with exercise tolerance, this study hypothesized that this is due to limitation of the maximal tidal volume (VT,(max)) during exercise by the reduced IC, The present study investigated the role of tidal FL at rest on: 1) the relationship of resting IC to VT,(max) and 2) on gas exchange during peak exercise in COPD patients.
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    Effect of inspiratory muscle training with an intermediate load on inspiratory power output in COPD
    (MUNKSGAARD INT PUBL LTD, 1998) Villafranca, C; Borzone, G; Leiva, A; Lisboa, C
    There is very little information about the effect of inspiratory muscle training on inspiratory how (V'I) and thus an power output (PO) in patients with chronic obstructive pulmonary disease (COPD). In this study me aimed to evaluate the changes induced by training on the determinants of pg),
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    Maleic anhydride-co-stearyl methacrylate copolymers. Synthesis, characterization, and some aspects of the solution behavior
    (MARCEL DEKKER INC, 1998) Leiva, A; Gargallo, L; Radic, D
    Maleic anhydride-stearyl methacrylate copolymer was synthesized by radical polymerization. The copolymer was fractionated and characterized by dynamic and static light scattering (DLS and SLS) experiments in different concentration regimes. Seven fractions of low polydispersity index(< 1.18) were studied. A typical behavior corresponding to good and theta (theta) solvents, according to the classical theories for polymers in solution, was found in the dilute regime. The results indicate in a semiquantitative way that this copolymer shows a normal behavior in the dilute regime. The rigidity parameters sigma and C-infinity show flexibility of the polymer chain, due to the incorporation of the maleic anhydride (MA) units, when the copolymer is compared with those corresponding to other poly(methacrylates) previously reported. In the semidilute regime and depending on the solvent nature, aggregation of the copolymer was detected. The aggregation was analyzed in terms of the values of the autocorrelation function determined by dynamic light scattering.
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    Modification of the air-water interface by a chitosan adsorption process. Effect on an amphiphilic polymer monolayer
    (WILEY, 2004) Gargallo, L; Leiva, A; Urzua, M; Alegria, L; Miranda, B; Radic, D
    Monolayer formation by poly[(maleic anhydride)-alt-(stearyl methacrylate)] (MA-alt-StM) on aqueous subphases, with and without chitosan, was studied by the Langmuir technique. Chitosan (CS) modified considerably the shape of the MA-alt-StM isotherms on water. To explain this behavior, the surface activity properties of chitosan at the air-solution interface were studied. The variations of the interfacial tension, gamma(int), with chitosan concentration and temperature, were also determined. The results were discussed in terms of the modification of the air-water interface owing to the presence of chitosan in the subphase and the surface activity. It was found that the standard free energy of adsorption, DeltaG(ads)(0),values were dependent on the degree of acetylation (DA) over the DA range being studied. (C) 2004 Society of Chemical Industry.
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    N-1-alkylitaconamic acids-co-styrene copolymers. Surface characterization
    (ELSEVIER SCI LTD, 2003) Miranda, B; Gargallo, L; Urzua, M; Leiva, A; Gonzalez Nilo, F; Radic, D
    A serie of six N-1-alkylitaconamic acids-co-styrene copolymers with alkyl groups varying in side chain length from 3 to 12 was used in this study. The surface behaviour of the copolymers has been studied as function of the side chain length. Contact angle data for two of these copolymer surfaces were obtained in water and several liquids. From this information the surface energy was determined. Differences in the wettability of N-1-alkylitaconamic acid-co-styrene are found. The results are discussed in terms of hydrophobic and polar effect of the copolymers. Results on spread monolayers characteristics of these copolymers on water surfaces are also reported. Surface pressure-area (pi-A) isotherms on a pure water subphase exhibit a transition region depending on the length of the alkyl side chain of the itaconamic acid moiety. It was also analyzed the phase transition in the monolayer at the air/water interface by brewster angle microscopy (BAM). Molecular mechanics approach was used to obtain predictions about the local interaction energies between segments. It was possible to conclude that the local interaction energies of propyl and decyl derivatives are quite similar while the hexyl derivative has higher interaction energy. The analysis of the coulombic energies together with the dispersion van der Waals energies (VDW) would be indicative, in first approximation, that carbonyl groups are more exposed in the case of propyl than in the other copolymers studied. (C) 2003 Elsevier Science Ltd. All rights reserved.