| 1. |
- Bachmann, M. Consuelo, et al.
(författare)
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Electrical impedance tomography in acute respiratory distress syndrome
- 2018
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Ingår i: Critical Care. - : BioMed Central. - 1364-8535 .- 1466-609X. ; 22
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Forskningsöversikt (refereegranskat)abstract
- Acute respiratory distress syndrome (ARDS) is a clinical entity that acutely affects the lung parenchyma, and is characterized by diffuse alveolar damage and increased pulmonary vascular permeability. Currently, computed tomography (CT) is commonly used for classifying and prognosticating ARDS. However, performing this examination in critically ill patients is complex, due to the need to transfer these patients to the CT room. Fortunately, new technologies have been developed that allow the monitoring of patients at the bedside. Electrical impedance tomography (EIT) is a monitoring tool that allows one to evaluate at the bedside the distribution of pulmonary ventilation continuously, in real time, and which has proven to be useful in optimizing mechanical ventilation parameters in critically ill patients. Several clinical applications of EIT have been developed during the last years and the technique has been generating increasing interest among researchers. However, among clinicians, there is still a lack of knowledge regarding the technical principles of EIT and potential applications in ARDS patients. The aim of this review is to present the characteristics, technical concepts, and clinical applications of EIT, which may allow better monitoring of lung function during ARDS.
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| 2. |
- Hurtado, Daniel E., et al.
(författare)
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Improving the Accuracy of Registration-Based Biomechanical Analysis : A Finite Element Approach to Lung Regional Strain Quantification
- 2016
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Ingår i: IEEE Transactions on Medical Imaging. - 0278-0062 .- 1558-254X. ; 35:2, s. 580-588
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Tidskriftsartikel (refereegranskat)abstract
- Tissue deformation plays an important role in lung physiology, as lung parenchyma largely deforms during spontaneous ventilation. However, excessive regional deformation may lead to lung injury, as observed in patients undergoing mechanical ventilation. Thus, the accurate estimation of regional strain has recently received great attention in the intensive care community. In this work, we assess the accuracy of regional strain maps computed from direct differentiation of B-Spline (BS) interpolations, a popular technique employed in non-rigid registration of lung computed tomography (CT) images. We show that, while BS-based registration methods give excellent results for the deformation transformation, the strain field directly computed from BS derivatives results in predictions that largely oscillate, thus introducing important errors that can even revert the sign of strain. To alleviate such spurious behavior, we present a novel finite-element (FE) method for the regional strain analysis of lung CT images. The method follows from a variational strain recovery formulation, and delivers a continuous approximation to the strain field in arbitrary domains. From analytical benchmarks, we show that the FE method results in errors that are a fraction of those found for the BS method, both in an average and pointwise sense. The application of the proposed FE method to human lung CT images results in 3D strain maps are heterogeneous and smooth, showing high consistency with specific ventilation maps reported in the literature. We envision that the proposed FE method will considerably improve the accuracy of image-based biomechanical analysis, making it reliable enough for routine medical applications.
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| 3. |
- Hurtado, Daniel E., et al.
(författare)
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Spatial patterns and frequency distributions of regional deformation in the healthy human lung
- 2017
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Ingår i: Biomechanics and Modeling in Mechanobiology. - : SPRINGER HEIDELBERG. - 1617-7959 .- 1617-7940. ; 16:4, s. 1413-1423
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Tidskriftsartikel (refereegranskat)abstract
- Understanding regional deformation in the lung has long attracted the medical community, as parenchymal deformation plays a key role in respiratory physiology. Recent advances in image registration make it possible to noninvasively study regional deformation, showing that volumetric deformation in healthy lungs follows complex spatial patterns not necessarily shared by all subjects, and that deformation can be highly anisotropic. In this work, we systematically study the regional deformation in the lungs of eleven human subjects by means of in vivo image-based biomechanical analysis. Regional deformation is quantified in terms of 3D maps of the invariants of the right stretch tensor, which are related to regional changes in length, surface and volume. Based on the histograms of individual lungs, we show that log-normal distributions adequately represent the frequency distribution of deformation invariants in the lung, which naturally motivates the normalization of the invariant fields in terms of the log-normal score. Normalized maps of deformation invariants allow for a direct intersubject comparison, as they display spatial patterns of deformation in a range that is common to all subjects. For the population studied, we find that lungs in supine position display a marked gradient along the gravitational direction not only for volumetric but also for length and surface regional deformation, highlighting the role of gravity in the regional deformation of normal lungs under spontaneous breathing.
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| 4. |
- Pham, Tai, et al.
(författare)
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Outcome of acute hypoxaemic respiratory failure : insights from the LUNG SAFE Study
- 2021
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Ingår i: European Respiratory Journal. - : European Respiratory Society. - 0903-1936 .- 1399-3003. ; 57:6
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Tidskriftsartikel (refereegranskat)abstract
- Background: Current incidence and outcome of patients with acute hypoxaemic respiratory failure requiring mechanical ventilation in the intensive care unit (ICU) are unknown, especially for patients not meeting criteria for acute respiratory distress syndrome (ARDS). Methods: An international, multicentre, prospective cohort study of patients presenting with hypoxaemia early in the course of mechanical ventilation, conducted during four consecutive weeks in the winter of 2014 in 459 ICUs from 50 countries (LUNG SAFE). Patients were enrolled with arterial oxygen tension/inspiratory oxygen fraction ratio <= 300 mmHg, new pulmonary infiltrates and need for mechanical ventilation with a positive end-expiratory pressure of >= 5 cmH(2)O. ICU prevalence, causes of hypoxaemia, hospital survival and factors associated with hospital mortality were measured. Patients with unilateral versus bilateral opacities were compared. Findings: 12 906 critically ill patients received mechanical ventilation and 34.9% with hypoxaemia and new infiltrates were enrolled, separated into ARDS (69.0%), unilateral infiltrate (22.7%) and congestive heart failure (CHF; 8.2%). The global hospital mortality was 38.6%. CHF patients had a mortality comparable to ARDS (44.1% versus 40.4%). Patients with unilateral-infiltrate had lower unadjusted mortality, but similar adjusted mortality compared to those with ARDS. The number of quadrants on chest imaging was associated with an increased risk of death. There was no difference in mortality comparing patients with unilateral-infiltrate and ARDS with only two quadrants involved. Interpretation: More than one-third of patients receiving mechanical ventilation have hypoxaemia and new infiltrates with a hospital mortality of 38.6%. Survival is dependent on the degree of pulmonary involvement whether or not ARDS criteria are reached.
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| 5. |
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| 6. |
- Retamal, Jaime, et al.
(författare)
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Does Regional Lung Strain Correlate With Regional Inflammation in Acute Respiratory Distress Syndrome During Nonprotective Ventilation? : An Experimental Porcine Study
- 2018
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Ingår i: Critical Care Medicine. - 0090-3493 .- 1530-0293. ; 46:6, s. e591-e599
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Tidskriftsartikel (refereegranskat)abstract
- OBJECTIVE: It is known that ventilator-induced lung injury causes increased pulmonary inflammation. It has been suggested that one of the underlying mechanisms may be strain. The aim of this study was to investigate whether lung regional strain correlates with regional inflammation in a porcine model of acute respiratory distress syndrome.DESIGN: Retrospective analysis of CT images and positron emission tomography images using [18F]fluoro-2-deoxy-D-glucose.SETTING: University animal research laboratory.SUBJECTS: Seven piglets subjected to experimental acute respiratory distress syndrome and five ventilated controls.INTERVENTIONS: Acute respiratory distress syndrome was induced by repeated lung lavages, followed by 210 minutes of injurious mechanical ventilation using low positive end-expiratory pressures (mean, 4 cm H2O) and high inspiratory pressures (mean plateau pressure, 45 cm H2O). All animals were subsequently studied with CT scans acquired at end-expiration and end-inspiration, to obtain maps of volumetric strain (inspiratory volume - expiratory volume)/expiratory volume, and dynamic positron emission tomography imaging. Strain maps and positron emission tomography images were divided into 10 isogravitational horizontal regions-of-interest, from which spatial correlation was calculated for each animal.MEASUREMENTS AND MAIN RESULTS: The acute respiratory distress syndrome model resulted in a decrease in respiratory system compliance (20.3 ± 3.4 to 14.0 ± 4.9 mL/cm H2O; p < 0.05) and oxygenation (PaO2/FIO2, 489 ± 80 to 92 ± 59; p < 0.05), whereas the control animals did not exhibit changes. In the acute respiratory distress syndrome group, strain maps showed a heterogeneous distribution with a greater concentration in the intermediate gravitational regions, which was similar to the distribution of [18F]fluoro-2-deoxy-D-glucose uptake observed in the positron emission tomography images, resulting in a positive spatial correlation between both variables (median R2 = 0.71 [0.02-0.84]; p < 0.05 in five of seven animals), which was not observed in the control animals.CONCLUSION: In this porcine acute respiratory distress syndrome model, regional lung strain was spatially correlated with regional inflammation, supporting that strain is a relevant and prominent determinant of ventilator-induced lung injury.
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| 7. |
- Retamal, Jaime, et al.
(författare)
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Non-lobar atelectasis generates inflammation and structural alveolar injury in the surrounding healthy tissue during mechanical ventilation
- 2014
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Ingår i: Critical Care. - : Springer Science and Business Media LLC. - 1364-8535 .- 1466-609X. ; 18:5, s. 505-
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Tidskriftsartikel (refereegranskat)abstract
- IntroductionWhen alveoli collapse the traction forces exerted on their walls by adjacent expanded units may increase and concentrate. These forces may promote its re-expansion at the expense of potentially injurious stresses at the interface between the collapsed and the expanded units. We developed an experimental model to test the hypothesis that a local non-lobar atelectasis can act as a stress concentrator, contributing to inflammation and structural alveolar injury in the surrounding healthy lung tissue during mechanical ventilation.MethodsA total of 35 rats were anesthetized, paralyzed and mechanically ventilated. Atelectasis was induced by bronchial blocking: after five minutes of stabilization and pre-oxygenation with FIO2 = 1.0, a silicon cylinder blocker was wedged in the terminal bronchial tree. Afterwards, the animals were randomized between two groups: 1) Tidal volume (VT) = 10 ml/kg and positive end-expiratory pressure (PEEP) = 3 cmH2O (VT10/PEEP3); and 2) VT = 20 ml/kg and PEEP = 0 cmH2O (VT20/zero end-expiratory pressure (ZEEP)). The animals were then ventilated during 180 minutes. Three series of experiments were performed: histological (n = 12); tissue cytokines (n = 12); and micro-computed tomography (microCT; n = 2). An additional six, non-ventilated, healthy animals were used as controls.ResultsAtelectasis was successfully induced in the basal region of the lung of 26 out of 29 animals. The microCT of two animals revealed that the volume of the atelectasis was 0.12 and 0.21 cm3. There were more alveolar disruption and neutrophilic infiltration in the peri-atelectasis region than the corresponding contralateral lung (control) in both groups. Edema was higher in the peri-atelectasis region than the corresponding contralateral lung (control) in the VT20/ZEEP than VT10/PEEP3 group. The volume-to-surface ratio was higher in the peri-atelectasis region than the corresponding contralateral lung (control) in both groups. We did not find statistical difference in tissue interleukin-1β and cytokine-induced neutrophil chemoattractant-1 between regions.ConclusionsThe present findings suggest that a local non-lobar atelectasis acts as a stress concentrator, generating structural alveolar injury and inflammation in the surrounding lung tissue.
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| 8. |
- Retamal, Jaime, et al.
(författare)
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Physiological and inflammatory consequences of high and low respiratory rate in acute respiratory distress syndrome
- 2021
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Ingår i: Acta Anaesthesiologica Scandinavica. - : John Wiley & Sons. - 0001-5172 .- 1399-6576. ; 65:8, s. 1013-1022
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Forskningsöversikt (refereegranskat)abstract
- Using protective mechanical ventilation strategies with low tidal volume is usually accompanied by an increment of respiratory rate to maintain adequate alveolar ventilation. However, there is no robust data that support the safety of a high respiratory rate concerning ventilator-induced lung injury. Several experimental animal studies have explored the effects of respiratory rate over lung physiology, using a wide range of frequencies and different models. Clinical evidence is scarce and restricted to the physiological impact of increased respiratory rate. Undoubtedly, the respiratory rate can influence respiratory mechanics in various ways as a factor of multiplication of the power of ventilation, and gas exchange, and also on alveolar dynamics. In this narrative review, we present our point of view over the main experimental and clinical evidence available regarding the effect of respiratory rate on ventilator-induced lung injury development.
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| 9. |
- Retamal, Jaime, et al.
(författare)
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Regional pulmonary deformation is positively correlated with regional lung inflammation assessed by 18F-FDG positron emission tomography / computed tomography
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Objective: Lung deformation beyond of physiological capacity is associated with cell death and inflammation. Lung strain has been estimated as a global strain, but uneven strain distribution may lead to regional stress concentrations and lung damage. Local lung inflammation can be estimated using PET imaging of [18F]fluoro-2-deoxy-D-glucose. We hypothesized that local lung deformation correlates well with local inflammation. The aim of this study was to assess local tidal deformations by using a new mathematical model of finite-elements to analyze CT images, and to correlate them with local inflammation in a porcine experimental model of early acute respiratory distress syndrome.Design: Retrospective images analysis, laboratory investigation.Setting: University animal research laboratory.Subjects: Seven piglets submitted to experimental ventilator-induced lung injury and five healthy ventilated controls.Intervention: Lung injury was induced by repeated lung lavages and 210 minutes of injurious mechanical ventilation using low positive end-expiratory pressure and high inspiratory pressures. All animals were subsequently studied with dynamic PET imaging of [18F]fluoro-2-deoxy-D-glucose. CT scans were acquired at end expiration and end inspiration. Then maps of deformation were constructed and regional deformation was estimated. We divided the lung parenchyma in 10 horizontal ROIs, and correlations of local volumetric strain and [18F]fluoro-2-deoxy-D-glucose uptake were analyzed in each ROI.Measurements and Main Results: The deformation maps showed a heterogeneous distribution with a greater concentration in the intermediate gravitational regions. We found a strong correlation between local strain and inflammation (R2 > 0.5) for the whole lung, when we eliminate the 3/10 dorsal ROIs R2 increased until>0.8.Conclusion: the present findings suggest that the greater local stretches were mainly concentrated in the intermediate gravitational zones of injured heterogeneous lungs. Additionally, local lung deformations correlated well with local inflammation in this experimental model of VILI. And the new proposed image-based estimation of regional volumetric strain based on finite element interpolations has the potential to give new insights of local pathogenic mechanisms of VILI and how best design protective-ventilations strategies.
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| 10. |
- Retamal Montes, Jaime, 1978-
(författare)
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Aspects on ventilation induced stress and strain on regional and global inflammation in experimental acute respiratory distress syndrome
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Mechanical ventilation (MV) is a life-saving therapy in acute respiratory distress syndrome (ARDS), a condition that affects 3000 patients/year in Sweden with a mortality rate of about 40%. However, MV may induce or worsen lung injury causing “ventilator-induced lung injury (VILI)”. From a mechanical perspective strain (deformation, or relative change in lung volume) and stress (tension) have been postulated as main determinants of VILI. High respiratory rate is potentially another factor that may exacerbate VILI by amplifying the total energy transmitted to the lungs during MV. In this thesis in animal ARDS models the hypotheses were that 1) lung parenchyma inhomogeneities concentrate stress and amplify lung damage and inflammation, 2) higher respiratory rates increase lung inflammation and lung edema in heterogeneous ARDS, and 3) local lung deformation is related to local inflammation.First, in a rat model the effect on inflammation and structural damage of regional lung collapse on the healthy surrounding lung tissue was assessed. Second, in porcine models the effect of respiratory rate on lung edema and inflammation was studied during two ventilatory modes; a) a permissive collapse mode and b) a homogenized lung parenchyma mode. Finally, lung deformation was correlated with lung inflammation assessed by positron emission tomography using 18F-FDG uptake.It was found that; 1) local inhomogeneities can act as stress amplifiers, increasing lung tissue inflammation and damage in the healthy surrounded lung. 2) high respiratory rate increases lung edema but decreases lung inflammation when permissive lung collapse is used and that these effects are prevented with lung parenchyma homogenization; 3) local lung deformation and inflammation are well correlated.In conclusion, lung inhomogeneities may aggravate VILI, respiratory rate may affect in different ways VILI progression depending on the ventilatory strategy, and finally, lung deformation is closely related to lung inflammation. With the caveat that the studies are performed in animal models, the results suggest that using ventilator strategies that homogenize the lungs, i.e., open collapsed lung regions and prevent re-collapse in ARDS will reduce VILI and in the end may decrease morbidity and the high mortality in this condition.
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| 11. |
- Retamal Montes, Jaime, 1978-, et al.
(författare)
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Open lung approach ventilation abolishes the negative effects of respiratory rate in experimental lung injury
- 2016
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Ingår i: Acta Anaesthesiologica Scandinavica. - : Wiley. - 0001-5172 .- 1399-6576. ; 60:8, s. 1131-1141
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: We recently reported that a high respiratory rate was associated with less inflammation than a low respiratory rate, but caused more pulmonary edema in a model of ARDS when an ARDSNet ventilatory strategy was used. We hypothesized that an open lung approach (OLA) strategy would neutralize the independent effects of respiratory rate on lung inflammation and edema. This hypothesis was tested in an ARDS model using two clinically relevant respiratory rates during OLA strategy.METHODS: Twelve piglets were subjected to an experimental model of ARDS and randomized into two groups: LRR (20 breaths/min) and HRR (40 breaths/min). They were mechanically ventilated for 6 h according to an OLA strategy. We assessed respiratory mechanics, hemodynamics, and extravascular lung water (EVLW). At the end of the experiment, wet/dry ratio, regional histology, and cytokines were evaluated.RESULTS: After the ARDS model was established, Cdyn,rs decreased from 21 ± 3.3 to 9.0 ± 1.8 ml/cmH2 O (P < 0.0001). After the lung recruitment maneuver, Cdyn,rs increased to the pre-injury value. During OLA ventilation, no differences in respiratory mechanics, hemodynamics, or EVLW were observed between groups. Wet/dry ratio and histological scores were not different between groups. Cytokine quantification was similar and showed a homogeneous distribution throughout the lung in both groups.CONCLUSION: Contrary to previous findings with the ARDSNet strategy, respiratory rate did not influence lung inflammatory response or pulmonary edema during OLA ventilation in experimental ARDS. This indicates that changing the respiratory rate when OLA ventilation is used will not exacerbate lung injury.
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