137 research outputs found
Recruitment maneuvers in acute respiratory distress syndrome and during general anesthesia
The use of low tidal volume ventilation and low to moderate positive end-expiratory pressure (PEEP) levels is a widespread strategy to ventilate patients with non-injured lungs during general anesthesia and in intensive care as well with mild to moderate acute respiratory distress syndrome (ARDS). Higher PEEP levels have been recommended in severe ARDS. Due to the presence of alveolar collapse, recruitment maneuvers (RMs) by causing a transient elevation in airway pressure (i.e. transpulmonary pressure) have been suggested to improve lung inflation in non-inflated and poorly-inflated lung regions. Various types of RMs such as sustained inflation at high pressure, intermittent sighs and stepwise increases of PEEP and/or airway plateau inspiratory pressure have been proposed. The use of RMs has been associated with mixed results in terms of physiological and clinical outcomes. The optimal method for RMs has not yet been identified. The use of RMs is not standardized and left to the individual physician based on his/her experience. Based on the same grounds, RMs have been proposed to improve lung aeration during general anesthesia. The aim of this review was to present the clinical evidence supporting the use of RMs in patients with ARDS and during general anesthesia and as well their potential biological effects in experimental models of acute lung injury
Axial vector current in an electromagnetic field and low-energy neutrino-photon interactions
An expression for the axial vector current in a strong, slowly varying
electromagnetic field is obtained. We apply this expression to the construction
of the effective action for low-energy neutrino-photon interactions.Comment: 6 pages, references updated, final version to appear in Phys. Rev.
Constraints on the Variation of the Fine Structure Constant from Big Bang Nucleosynthesis
We put bounds on the variation of the value of the fine structure constant
, at the time of Big Bang nucleosynthesis. We study carefully all light
elements up to Li. We correct a previous upper limit on estimated from He primordial abundance and we find interesting new
potential limits (depending on the value of the baryon-to-photon ratio) from
Li, whose production is governed to a large extent by Coulomb barriers. The
presently unclear observational situation concerning the primordial abundances
preclude a better limit than |\Delta \alpha/\alpha| \lsim 2\cdot 10^{-2}, two
orders of magnitude less restrictive than previous bounds. In fact, each of the
(mutually exclusive) scenarios of standard Big Bang nucleosynthesis proposed,
one based on a high value of the measured deuterium primordial abundance and
one based on a low value, may describe some aspects of data better if a change
in of this magnitude is assumed.Comment: 21 pages, eps figures embedded using epsfig macr
Controle da ferrugem da folha do trigo (Puccinia triticina) em diferentes momentos de aplicação de fungicida
Meccanismi di comunicazione in specie simpatriche di formiche mietitrici del genere Messor (Hymenoptera, Formicidae
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