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Now showing items 17 - 18 of 18

  • Effects of Positive End-Expiratory Pressure and Body Position on Pulmonary Blood Flow Redistribution in Mechanically Ventilated Normal Pigs

    Richard, Jean-Christophe   Decailliot, Francois   Janier, Marc   Annat, Guy   Guérin, Claude  

    Study objectives: To assess the respective effects of position and positive end-expiratory pressure (PEEP) on the distribution of regional pulmonary blood flow (PBF). Design: Prospective randomized animal study. Setting: Animal research facility in a university hospital. Participants: Normal pigs that were tracheostomized, anesthetized, and mechanically ventilated. Interventions: PBF was measured in seven pigs in the supine position (SP) and the prone position (PP) at both zero end-expiratory pressure (ZEEP) and 10 cm H(2)O of PEEP. The regional PBF was assessed by the radioactive microsphere method. The lungs from each pig were sliced into 90 samples. The heterogeneity of PBF was estimated from its coefficient of variation. Measurements and results: The lung samples had a mean (+/- SD) weight of 1.60 +/- 0.39 g. Changing position from SP to PP at ZEEP redistributed PBF toward the anterior, superior, and peripheral regions and did not significantly reduce the coefficient of variation for regional PBF (reduction, 44.7 +/- 7% to 42.2 +/- 8%). Changing from the SP to PP position at PEEP induced a similar, but more marked, redistribution of PBF and a significant reduction in the coefficient of variation from 53 +/- 13% to 30.4 +/- 7% (p < 0.001). In the SP, PEEP redistributed PBF toward the posterior, inferior, and central regions without changing the heterogeneity of PBF. In the PP, PEEP had little effect on the PBF redistribution but significantly reduced the coefficient of variation of PBF from 42.2 +/- 8% to 30.4 +/- 7% (p < 0.05). Conclusions: Pigs in the PP had altered gravitational dependence of PBF compared to that observed when pigs were in the SP. This effect was enhanced by using a PEEP of 10 cm H(2)O.
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  • Polarization dependent formalism of interferometric structures describing DPSK and DQPSK receivers

    Chen, Lawrence R.   Samadi, Payman   Richard, Jean-Christophe   Lize, Yannick Keith  

    We describe a polarization dependent formalism for DPSK and DQPSK receivers and show that the combined effect of PDL and PDFS cannot be decoupled making the birefringence axes non-orthogonal and independent of PDL axes.
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