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Sökning: WFRF:(Jonson Björn)

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1.
  • Bitzén, Ulrika, et al. (författare)
  • Dynamic elastic pressure-volume loops in healthy pigs recorded with inspiratory and expiratory sinusoidal flow modulationRelationship to static pressure-volume loops.
  • 2004
  • Ingår i: Intensive Care Medicine. - Springer. - 0342-4642. ; 30:3, s. 481-488
  • Tidskriftsartikel (refereegranskat)abstract
    • Objective: The objective was to analyse relationships between inspiratory and expiratory static and dynamic elastic pressure-volume (P-el/V) curves in healthy pigs. Design: The modulated low flow method was developed to allow studies also of the expiratory P-el/V curves. Static P-el/V (P-el,P-st/V) and dynamic P-el/V (P-el,P-dyn/V) loops were studied in healthy pigs. Setting: Animal research laboratory in a university hospital. Material: Ten healthy anaesthetised and paralysed pigs. Interventions and measurements: A computer controlled a Servo Ventilator 900C with respect to respiratory rate, inspiratory flow and expiratory pressure to achieve a sinusoidal modulation of inspiration and expiration for determination of P-el,P-dyn/V loops from zero end-expiratory pressure (ZEEP) and from a positive end-expiratory pressure (PEEP) of 6 cmH(2)O to 20, 35 and 50 cmH(2)O. The same system was used for studies of P-el,P-st/V loops with the flow-interruption method from ZEEP and PEEP to 35 cmH(2)O. Recordings were analysed with an iterative technique. Results: The feasibility of automated determination of P-el,P-dyn/V loops was demonstrated. Differences between P-el,P-dyn/V and P-el,P-st/V loops were explained by viscoelastic behaviour. P-el,P-st/V loops recorded from PEEP to 35 cmH(2)O showed no significant hysteresis, indicating a non-significant surface tension hysteresis. P-el,P-dyn/V loops from PEEP and both P-el,P-st/V and P-el,P-dyn/V loops from ZEEP to 35 cmH(2)O showed hysteresis. This indicates that lung collapse/re-expansion caused P-el/V loop hysteresis which, in P-el,P-dyn/V loops, was augmented by viscoelastic behaviour. Conclusions: Viscoelasticity influences P-el,P-dyn/V curves. Hysteresis caused by surface tension merits re-evaluation. Lung collapse and re-expansion may be indicated by hysteresis of P-el/V loops.
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3.
  • Uttman, Leif, et al. (författare)
  • Computer simulation allows goal-oriented mechanical ventilation in acute respiratory distress syndrome
  • 2007
  • Ingår i: Critical Care. - BioMed Central. - 1364-8535. ; 11:2
  • Tidskriftsartikel (refereegranskat)abstract
    • Introduction To prevent further lung damage in patients with acute respiratory distress syndrome ( ARDS), it is important to avoid overdistension and cyclic opening and closing of atelectatic alveoli. Previous studies have demonstrated protective effects of using low tidal volume ( VT), moderate positive end-expiratory pressure and low airway pressure. Aspiration of dead space ( ASPIDS) allows a reduction in VT by eliminating dead space in the tracheal tube and tubing. We hypothesized that, by applying goal-orientated ventilation based on iterative computer simulation, VT can be reduced at high respiratory rate and much further reduced during ASPIDS without compromising gas exchange or causing high airway pressure. Methods ARDS was induced in eight pigs by surfactant perturbation and ventilator-induced lung injury. Ventilator resetting guided by computer simulation was then performed, aiming at minimal VT, plateau pressure 30 cmH(2)O and isocapnia, first by only increasing respiratory rate and then by using ASPIDS as well. Results VT decreased from 7.2 +/- 0.5 ml/kg to 6.6 +/- 0.5 ml/kg as respiratory rate increased from 40 to 64 +/- 6 breaths/min, and to 4.0 +/- 0.4 ml/kg when ASPIDS was used at 80 +/- 6 breaths/min. Measured values of arterial carbon dioxide tension were close to predicted values. Without ASPIDS, total positive end-expiratory pressure and plateau pressure were slightly higher than predicted, and with ASPIDS they were lower than predicted. Conclusion In principle, computer simulation may be used in goal-oriented ventilation in ARDS. Further studies are needed to investigate potential benefits and limitations over extended study periods.
4.
  • Aboab, J., et al. (författare)
  • CO2 elimination at varying inspiratory pause in acute lung injury
  • 2007
  • Ingår i: Clinical Physiology and Functional Imaging. - Wiley Online Library. - 1475-0961. ; 27:1, s. 2-6
  • Tidskriftsartikel (refereegranskat)abstract
    • Previous studies have indicated that, during mechanical ventilation, an inspiratory pause enhances gas exchange. This has been attributed to prolonged time during which fresh gas of the tidal volume is present in the respiratory zone and is available for distribution in the lung periphery. The mean distribution time of inspired gas (MDT) is the mean time during which fractions of fresh gas are present in the respiratory zone. All ventilators allow setting of pause time, T-P, which is a determinant of MDT. The objective of the present study was to test in patients the hypothesis that the volume of CO2 eliminated per breath, VTCO2, is correlated to the logarithm of MDT as previously found in animal models. Eleven patients with acute lung injury were studied. When T-P increased from 0% to 30%, MDT increased fourfold. A change of T-P from 10% to 0% reduced VTCO2 by 14%, while a change to 30% increased VTCO2 by 19%. The relationship between VTCO2 and MDT was in accordance with the logarithmic hypothesis. The change in VTCO2 reflected to equal extent changes in airway dead space and alveolar PCO2 read from the alveolar plateau of the single breath test for CO2. By varying T-P, effects are observed on VTCO2, airway dead space and alveolar PCO2. These effects depend on perfusion, gas distribution and diffusion in the lung periphery, which need to be further elucidated.
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  • Aboab, Jerome, et al. (författare)
  • Dead space and CO2 elimination related to pattern of inspiratory gas delivery in ARDS patients
  • 2012
  • Ingår i: Critical Care. - BioMed Central. - 1364-8535. ; 16:2
  • Tidskriftsartikel (refereegranskat)abstract
    • Introduction: The inspiratory flow pattern influences CO2 elimination by affecting the time the tidal volume remains resident in alveoli. This time is expressed in terms of mean distribution time (MDT), which is the time available for distribution and diffusion of inspired tidal gas within resident alveolar gas. In healthy and sick pigs, abrupt cessation of inspiratory flow (that is, high end-inspiratory flow (EIF)), enhances CO2 elimination. The objective was to test the hypothesis that effects of inspiratory gas delivery pattern on CO2 exchange can be comprehensively described from the effects of MDT and EIF in patients with acute respiratory distress syndrome (ARDS). Methods: In a medical intensive care unit of a university hospital, ARDS patients were studied during sequences of breaths with varying inspiratory flow patterns. Patients were ventilated with a computer-controlled ventilator allowing single breaths to be modified with respect to durations of inspiratory flow and postinspiratory pause (T-P), as well as the shape of the inspiratory flow wave. From the single-breath test for CO2, the volume of CO2 eliminated by each tidal breath was derived. Results: A long MDT, caused primarily by a long TP, led to importantly enhanced CO2 elimination. So did a high EIF. Effects of MDT and EIF were comprehensively described with a simple equation. Typically, an efficient and a less-efficient pattern of inspiration could result in +/- 10% variation of CO2 elimination, and in individuals, up to 35%. Conclusions: In ARDS, CO2 elimination is importantly enhanced by an inspiratory flow pattern with long MDT and high EIF. An optimal inspiratory pattern allows a reduction of tidal volume and may be part of lung-protective ventilation.
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  • Aksyutina, Y., et al. (författare)
  • Momentum profile analysis in one-neutron knockout from Borromean nuclei
  • 2013
  • Ingår i: Physics Letters B. - 0370-2693. ; 718:4-5, s. 1309-1313
  • Tidskriftsartikel (refereegranskat)abstract
    • One-neutron knockout reactions from Borromean nuclei are analyzed using a profile function analysis technique. The profile function, which is derived as the square root of the variance of the measured fragment + neutron momenta as a function of their relative energy, is shown to be very sensitive to the angular momentum of the knocked out neutron. Three cases are studied here: He-7, where the profile function analysis shows a presence of (s(1/2))(2) component in the He-8 ground-state wave-function, Li-10, where the presence of a 11(2)% d-wave contribution to the relative energy spectrum above 1.5 MeV is found and, finally, the presence of a major s contribution around 0.5 MeV relative energy in the Be-13 case and that the observed decay to the Be-12 2(+) state originates in a d state in Be-13.
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