A more gradual positive end-expiratory pressure increase reduces lung damage and improves cardiac function in experimental acute respiratory distress syndrome.

Increases in positive end-expiratory pressure (PEEP) or recruitment maneuvers may increase stress in lung parenchyma, extracellular matrix, and lung vessels; however, adaptative responses may occur. We evaluated the effects of PEEP on lung damage and cardiac function when increased abruptly, gradually, or more gradually in experimental mild/moderate acute respiratory distress syndrome (ARDS) induced by Escherichia coli lipopolysaccharide intratracheally. After 24 h, Wistar rats (n = 48) were randomly assigned to four mechanical ventilation strategies according to PEEP levels: 1) 3 cmH2O for 2 h (control); 2) 3 cmH2O for 1 h followed by an abrupt increase to 9 cmH2O for 1 h (no adaptation time); 3) 3 cmH2O for 30 min followed by a gradual increase to 9 cmH2O over 30 min then kept constant for 1 h (shorter adaptation time); and 4) more gradual increase in PEEP from 3 cmH2O to 9 cmH2O over 1 h and kept constant thereafter (longer adaptation time). At the end of the experiment, oxygenation improved in the shorter and longer adaptation time groups compared with the no-adaptation and control groups. Diffuse alveolar damage and expressions of interleukin-6, club cell protein-16, vascular cell adhesion molecule-1, amphiregulin, decorin, and syndecan were higher in no adaptation time compared with other groups. Pulmonary arterial pressure was lower in longer adaptation time than in no adaptation (P = 0.002) and shorter adaptation time (P = 0.025) groups. In this model, gradually increasing PEEP limited lung damage and release of biomarkers associated with lung epithelial/endothelial cell and extracellular matrix damage, as well as the PEEP-associated increase in pulmonary arterial pressure.NEW & NOTEWORTHY In a rat model of Escherichia coli lipopolysaccharide-induced mild/moderate acute respiratory distress syndrome, a gradual PEEP increase (shorter adaptation time) effectively mitigated histological lung injury and biomarker release associated with lung inflammation, damage to epithelial cells, endothelial cells, and the extracellular matrix compared with an abrupt increase in PEEP. A more gradual PEEP increase (longer adaptation time) decreased lung damage, pulmonary vessel compression, and pulmonary arterial pressure.

Biological impact of restrictive and liberal fluid strategies at low and high PEEP levels on lung and distal organs in experimental acute respiratory distress syndrome.

Background: Fluid regimens in acute respiratory distress syndrome (ARDS) are conflicting. The amount of fluid and positive end-expiratory pressure (PEEP) level may interact leading to ventilator-induced lung injury (VILI). We therefore evaluated restrictive and liberal fluid strategies associated with low and high PEEP levels with regard to lung and kidney damage, as well as cardiorespiratory function in endotoxin-induced ARDS. Methods: Thirty male Wistar rats received an intratracheal instillation of Escherichia coli lipopolysaccharide. After 24 h, the animals were anesthetized, protectively ventilated (VT = 6 ml/kg), and randomized to restrictive (5 ml/kg/h) or liberal (40 ml/kg/h) fluid strategies (Ringer lactate). Both groups were then ventilated with PEEP = 3 cmH2O (PEEP3) and PEEP = 9 cmH2O (PEEP9) for 1 h (n = 6/group). Echocardiography, arterial blood gases, and lung mechanics were evaluated throughout the experiments. Histologic analyses were done on the lungs, and molecular biology was assessed in lungs and kidneys using six non-ventilated animals with no fluid therapy. Results: In lungs, the liberal group showed increased transpulmonary plateau pressure compared with the restrictive group (liberal, 23.5 ± 2.9 cmH2O; restrictive, 18.8 ± 2.3 cmH2O, p = 0.046) under PEEP = 9 cmH2O. Gene expression associated with inflammation (interleukin [IL]-6) was higher in the liberal-PEEP9 group than the liberal-PEEP3 group (p = 0.006) and restrictive-PEEP9 (p = 0.012), Regardless of the fluid strategy, lung mechanical power and the heterogeneity index were higher, whereas birefringence for claudin-4 and zonula-ocludens-1 gene expression were lower in the PEEP9 groups. Perivascular edema was higher in liberal groups, regardless of PEEP levels. Markers related to damage to epithelial cells [club cell secreted protein (CC16)] and the extracellular matrix (syndecan) were higher in the liberal-PEEP9 group than the liberal-PEEP3 group (p = 0.010 and p = 0.024, respectively). In kidneys, the expression of IL-6 and neutrophil gelatinase-associated lipocalin was higher in PEEP9 groups, regardless of the fluid strategy. For the liberal strategy, PEEP = 9 cmH2O compared with PEEP = 3 cmH2O reduced the right ventricle systolic volume (37%) and inferior vena cava collapsibility index (45%). Conclusion: The combination of a liberal fluid strategy and high PEEP led to more lung damage. The application of high PEEP, regardless of the fluid strategy, may also be deleterious to kidneys.

Impact of experimental obesity on diaphragm structure, function, and bioenergetics.

Obesity is associated with bioenergetic dysfunction of peripheral muscles; however, little is known regarding the impact of obesity on the diaphragm. We hypothesized that obesity would be associated with diaphragm dysfunction attributable to mitochondrial oxygen consumption and structural and ultrastructural changes. Wistar rat litters were culled to 3 pups to induce early postnatal overfeeding and consequent obesity. Control animals were obtained from unculled litters. From postnatal day 150, diaphragm ultrasound, computed tomography, high-resolution respirometry, immunohistochemical, biomolecular, and ultrastructural histological analyses were performed. The diaphragms of obese animals, compared with those of controls, presented changes in morphology as increased thickening fraction, diaphragm excursion, and diaphragm dome height, as well as increased mitochondrial respiratory capacity coupled to ATP synthesis and maximal respiratory capacity. Fatty acid synthase gene expression was also higher in obese animals, suggesting a source of energy for the respiratory chain. Myosin heavy chain-IIA was increased, indicating shift from glycolytic toward oxidative muscle fiber profile. Diaphragm tissue also exhibited ultrastructural changes, such as compact, round, and swollen mitochondria with fainter cristae and more lysosomal bodies. Dynamin-1 expression in the diaphragm was reduced in obese rats, suggesting decreased mitochondrial fission. Furthermore, gene expressions of peroxisome γ proliferator-activated receptor coactivator-1α and superoxide dismutase-2 were lower in obese animals than in controls, which may indicate a predisposition to oxidative injury. In conclusion, in the obesity model used herein, muscle fiber phenotype was altered in a manner likely associated with increased mitochondrial respiratory capability, suggesting respiratory adaptation to increased metabolic demand.NEW & NOTEWORTHY Obesity has been associated with peripheral muscle dysfunction; however, little is known about its impact on the diaphragm. In the current study, we found high oxygen consumption in diaphragm tissue and changes in muscle fiber phenotypes toward a more oxidative profile in experimental obesity.