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- Aboab, J., et al.
(författare)
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CO2 elimination at varying inspiratory pause in acute lung injury
- 2007
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Ingår i: Clinical Physiology and Functional Imaging. - 1475-0961. ; 27:1, s. 2-6
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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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| 2. |
- Aboab, Jerome, et al.
(författare)
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Dead space and CO2 elimination related to pattern of inspiratory gas delivery in ARDS patients
- 2012
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Ingår i: Critical Care. - : Springer Science and Business Media LLC. - 1364-8535. ; 16:2
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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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| 3. |
- Aboab, Jerome, et al.
(författare)
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Effect of inspired oxygen fraction on alveolar derecruitment in acute respiratory distress syndrome
- 2006
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Ingår i: Intensive Care Medicine. - : Springer Science and Business Media LLC. - 0342-4642 .- 1432-1238. ; 32:12, s. 1979-1986
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Tidskriftsartikel (refereegranskat)abstract
- Objective: High fractions of inspired oxygen (FIO2) used in acute lung injury (ALI) may promote resorption atelectasis. The impact of derecruitment related to high FIO2 in ALI is debated. We evaluated derecruitment with 100% vs. 60% FIO2 at two levels of positive end-expiratory pressure (PEEP). Patients: Fourteen consecutive patients with ALI were studied. Interventions: Recruited volume at two PEEP levels was computed from two pressure-volume curves, recorded from PEEP and from zero end-expiratory pressure, using the sinusoidal flow modulation method. PEEP-induced recruitment was measured during prolonged expiration as the difference between the two curves at a given pressure. PaO2/FIO2 was also measured. PEEP was 5 +/- 1 or 14 +/- 3 cmH(2)O and FIO2 was 60% or 100%, yielding four combinations. We looked for differences between the beginning and end of a 30-min period with each combination. Measurement and results: With low PEEP and 100% FIO2, recruited volume decreased significantly from 68 +/- 53 to 39 +/- 43 ml and PaO2/FIO2 from 196 +/- 104 to 153 +/- 83 mmHg. With the three other combinations (low PEEP and 60% FIO2 or high PEEP and 60% or 100% FIO2) none of the parameters decreased significantly. Conclusion: In mechanically ventilated patients with ALI the breathing of pure oxygen leads to derecruitment, which is prevented by high PEEP.
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| 5. |
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| 6. |
- Bitzén, Ulrika, et al.
(författare)
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Dynamic elastic pressure-volume loops in healthy pigs recorded with inspiratory and expiratory sinusoidal flow modulationRelationship to static pressure-volume loops.
- 2004
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Ingår i: Intensive Care Medicine. - : Springer Science and Business Media LLC. - 0342-4642 .- 1432-1238. ; 30:3, s. 481-488
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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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| 7. |
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| 8. |
- Bitzén, Ulrika, et al.
(författare)
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Measurement and mathematical modelling of elastic and resistive lung mechanical properties studied at sinusoidal expiratory flow.
- 2010
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Ingår i: Clinical Physiology and Functional Imaging. - 1475-0961. ; 30, s. 439-446
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Tidskriftsartikel (refereegranskat)abstract
- Summary Elastic pressure/volume (P(el)/V) and elastic pressure/resistance (P(el)/R) diagrams reflect parenchymal and bronchial properties, respectively. The objective was to develop a method for determination and mathematical characterization of P(el)/V and P(el)/R relationships, simultaneously studied at sinusoidal flow-modulated vital capacity expirations in a body plethysmograph. Analysis was carried out by iterative parameter estimation based on a composite mathematical model describing a three-segment P(el)/V curve and a hyperbolic P(el)/R curve. The hypothesis was tested that the sigmoid P(el)/V curve is non-symmetric. Thirty healthy subjects were studied. The hypothesis of a non-symmetric P(el)/V curve was verified. Its upper volume asymptote was nearly equal to total lung capacity (TLC), indicating lung stiffness increasing at high lung volume as the main factor limiting TLC at health. The asymptotic minimal resistance of the hyperbolic P(el)/R relationship reflected lung size. A detailed description of both P(el)/V and P(el)/R relationships was simultaneously derived from sinusoidal flow-modulated vital capacity expirations. The nature of the P(el)/V curve merits the use of a non-symmetric P(el)/V model.
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| 9. |
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| 10. |
- Devaquet, Jerome, et al.
(författare)
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Effects of inspiratory pause on CO2 elimination and arterial PCO2 in acute lung injury
- 2008
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Ingår i: Journal of Applied Physiology. - : American Physiological Society. - 1522-1601 .- 8750-7587. ; 105:6, s. 1944-1949
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Tidskriftsartikel (refereegranskat)abstract
- A high respiratory rate associated with the use of small tidal volumes, recommended for acute lung injury (ALI), shortens time for gas diffusion in the alveoli. This may decrease CO2 elimination. We hypothesized that a postinspiratory pause could enhance CO2 elimination and reduce PaCO2 by reducing dead space in ALI. In 15 mechanically ventilated patients with ALI and hypercapnia, a 20% postinspiratory pause (Tp20) was applied during a period of 30 min between two ventilation periods without postinspiratory pause (Tp0). Other parameters were kept unchanged. The single breath test for CO2 was recorded every 5 min to measure tidal CO2 elimination (VtCO(2)), airway dead space (V-Daw), and slope of the alveolar plateau. PaO2, PaCO2, and physiological and alveolar dead space (V-Dphys, V-Dalv) were determined at the end of each 30-min period. The postinspiratory pause, 0.7 +/- 0.2 s, induced on average < 0.5 cmH(2)O of intrinsic positive end-expiratory pressure (PEEP). During Tp20, VtCO(2) increased immediately by 28 +/- 10% (14 +/- 5 ml per breath compared with 11 +/- 4 for Tp0) and then decreased without reaching the initial value within 30 min. The addition of a postinspiratory pause significantly decreased V-Daw by 14% and V-Dphys by 11% with no change in V-Dalv. During Tp20, the slope of the alveolar plateau initially fell to 65 +/- 10% of baseline value and continued to decrease. Tp20 induced a 10 +/- 3% decrease in PaCO2 at 30 min (from 55 +/- 10 to 49 +/- 9 mmHg, P < 0.001) with no significant variation in PaO2. Postinspiratory pause has a significant influence on CO2 elimination when small tidal volumes are used during mechanical ventilation for ALI.
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