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Romero P.V.,Laboratory of Experimental Pneumology | Romero P.V.,University of Barcelona | Faffe D.S.,Federal University of Rio de Janeiro | Canete C.,Laboratory of Experimental Pneumology
Journal of Applied Physiology | Year: 2011

Harmonic distortion (HD) is a simple approach to analyze lung tissue nonlinear phenomena. This study aimed to characterize frequency-dependent behavior of HD at several amplitudes in lung tissue strips from healthy rats and its influence on the parameters of linear analysis. Lung strips (n = 17) were subjected to sinusoidal deformation at three different strain amplitudes (Δε) and fixed operational stress (12 hPa) among various frequencies, between 0.03 and 3 Hz. Input HD was <2% in all cases. The main findings in our study can be summarized as follows: 1) harmonic distortion of stress (HD) showed a positive frequency and amplitude dependence following a power law with frequency; 2) HD correlated significantly with the frequency response of dynamic elastance, seeming to converge to a limited range at an extrapolated point where HD=0; 3) the relationship between tissue damping (G) and HDω= 1 (the harmonic distortion at ω=1 rad/s) was linear and accounted for a large part of the interindividual variability of G; 4) hysteresivity depended linearly on κ (the power law exponent of HD with ω); and 5) the error of the constant phase model could be corrected by taking into account the frequency dependence of harmonic distortion. We concluded that tissue elasticity and tissue damping are coupled at the level of the stress-bearing element and to the mechanisms underlying dynamic nonlinearity of lung tissue. Copyright © 2011 the American Physiological Society.


Lopez-Aguilar J.,Fundacio Parc Tauli | Lopez-Aguilar J.,Autonomous University of Barcelona | Lopez-Aguilar J.,Critical Care Center | Lopez-Aguilar J.,CIBER ISCIII | And 14 more authors.
Respiratory Physiology and Neurobiology | Year: 2015

We determined whether the combination of low dose partial liquid ventilation (PLV) with perfluorocarbons (PFC) and prone positioning improved lung function while inducing minimal stress. Eighteen pigs with acute lung injury were assigned to conventional mechanical ventilation (CMV) or PLV (5 or 10. ml/kg of PFC). Positive end-expiratory pressure (PEEP) trials in supine and prone positions were performed. Data were analyzed by a multivariate polynomial regression model. The interplay between PLV and position depended on the PEEP level. In supine PLV dampened the stress induced by increased PEEP during the trial. The PFC dose of 5. ml/kg was more effective than the dose 10. ml/kg. This effect was not observed in prone. Oxygenation was significantly higher in prone than in supine position mainly at lower levels of PEEP. In conclusion, MV settings should take both gas exchange and stress/strain into account. When protective CMV fails, rescue strategies combining prone positioning and PLV with optimal PEEP should improve gas exchange with minimal stress. © 2015 Elsevier B.V.


Pinart M.,Laboratory of Experimental Pneumology | Faffe D.S.,Federal University of Rio de Janeiro | Sapina M.,Laboratory of Experimental Pneumology | Romero P.V.,Laboratory of Experimental Pneumology | Romero P.V.,University of Barcelona
Journal of Applied Physiology | Year: 2011

Pinart M, Faffe DS, Sapiña M, Romero PV. Dynamic nonlinearity of lung tissue: effects of strain amplitude and stress level. J Appl Physiol 110: 653-660, 2011. First published December 16, 2010; doi:10.1152/japplphysiol. 01115.2010.-Lung tissue presents substantial nonlinear phenomena not accounted for by linear models; however, nonlinear approaches are less available. Our aim was to characterize the behavior of total harmonic distortion, an index of nonlinearity, in lung tissue strips under sinusoidal deformation at a single frequency as a function of strain amplitude and operational stress. To that end, lung parenchymal strips from healthy rats (n = 6) were subjected to sinusoidal deformation (1 Hz) at different strain amplitudes (δε = 4, 8, 12, 16, and 20%) and operating stresses (σop 6, 8, 10, 12, 14, and 16 hPa). Additional rats (n = 9) were intratracheally instilled with saline or bleomycin (2.5 U/kg, 3 times 1 wk apart), killed 28 days after the last instillation, and their lung tissue strips were studied at 5 and 10 hPa σop and 5% δε. In both cases, harmonic distortion (HD%) of input (strain) and output (stress) signals were determined. In healthy strips, HD% increased linearly with δε, stress amplitude, and minimum stress by cycle variations, but showed no significant change with σop levels. A prediction model could be determined as a function of operational stress and stress amplitude. Harmonic distortion was significantly increased in bleomycin-treated strips compared with controls and showed positive correlation with E behavior in both normal and diseased strips. We concluded that HD% can be useful as a single and simple parameter of lung tissue nonlinearity. © 2011 the American Physiological Society.

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