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Regional distribution of acoustic-based lung vibration as a function of mechanical ventilation mode.

ABSTRACT: INTRODUCTION: There are several ventilator modes that are used for maintenance mechanical ventilation but no conclusive evidence that one mode of ventilation is better than another. Vibration response imaging is a novel bedside imaging technique that displays vibration energy of lung sounds generated during the respiratory cycle as a real-time structural and functional image of the respiration process. In this study, we objectively evaluated the differences in regional lung vibration during different modes of mechanical ventilation by means of this new technology. METHODS: Vibration response imaging was performed on 38 patients on assist volume control, assist pressure control, and pressure support modes of mechanical ventilation with constant tidal volumes. Images and vibration intensities of three lung regions at maximal inspiration were analyzed. RESULTS: There was a significant increase in overall geographical area (p < 0.001) and vibration intensity (p < 0.02) in pressure control and pressure support (greatest in pressure support), compared to volume control, when each patient served as his or her own control while targeting the same tidal volume in each mode. This increase in geographical area and vibration intensity occurred primarily in the lower lung regions. The relative percentage increases were 28.5% from volume control to pressure support and 18.8% from volume control to pressure control (p < 0.05). Concomitantly, the areas of the image in the middle lung regions decreased by 3.6% from volume control to pressure support and by 3.7% from volume control to pressure control (p < 0.05). In addition, analysis of regional vibration intensity showed a 35.5% relative percentage increase in the lower region with pressure support versus volume control (p < 0.05). CONCLUSION: Pressure support and (to a lesser extent) pressure control modes cause a shift of vibration toward lower lung regions compared to volume control when tidal volumes are held constant. Better patient synchronization with the ventilator, greater downward movement of the diaphragm, and decelerating flow waveform are potential physiologic explanations for the redistribution of vibration energy to lower lung regions in pressure-targeted modes of mechanical ventilation.

SUBMITTER: Dellinger RP

PROVIDER: S-EPMC2151859 | biostudies-other | 2007

REPOSITORIES: biostudies-other

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Regional distribution of acoustic-based lung vibration as a function of mechanical ventilation mode.

Dellinger R Phillip RP Jean Smith S Cinel Ismail I Tay Christina C Rajanala Susmita S Glickman Yael A YA Parrillo Joseph E JE

Critical care (London, England) 20070101 1

<h4>Introduction</h4>There are several ventilator modes that are used for maintenance mechanical ventilation but no conclusive evidence that one mode of ventilation is better than another. Vibration response imaging is a novel bedside imaging technique that displays vibration energy of lung sounds generated during the respiratory cycle as a real-time structural and functional image of the respiration process. In this study, we objectively evaluated the differences in regional lung vibration duri ...[more]

PMID: 17316449

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Project description:BACKGROUND:Protective mechanical ventilation (MV) aims at limiting global lung deformation and has been associated with better clinical outcomes in acute respiratory distress syndrome (ARDS) patients. In ARDS lungs without MV support, the mechanisms and evolution of lung tissue deformation remain understudied. In this work, we quantify the progression and heterogeneity of regional strain in injured lungs under spontaneous breathing and under MV. METHODS:Lung injury was induced by lung lavage in murine subjects, followed by 3 h of spontaneous breathing (SB-group) or 3 h of low Vt mechanical ventilation (MV-group). Micro-CT images were acquired in all subjects at the beginning and at the end of the ventilation stage following induction of lung injury. Regional strain, strain progression and strain heterogeneity were computed from image-based biomechanical analysis. Three-dimensional regional strain maps were constructed, from which a region-of-interest (ROI) analysis was performed for the regional strain, the strain progression, and the strain heterogeneity. RESULTS:After 3 h of ventilation, regional strain levels were significantly higher in 43.7% of the ROIs in the SB-group. Significant increase in regional strain was found in 1.2% of the ROIs in the MV-group. Progression of regional strain was found in 100% of the ROIs in the SB-group, whereas the MV-group displayed strain progression in 1.2% of the ROIs. Progression in regional strain heterogeneity was found in 23.4% of the ROIs in the SB-group, while the MV-group resulted in 4.7% of the ROIs showing significant changes. Deformation progression is concurrent with an increase of non-aerated compartment in SB-group (from 13.3%?±?1.6% to 37.5%?±?3.1%), being higher in ventral regions of the lung. CONCLUSIONS:Spontaneous breathing in lung injury promotes regional strain and strain heterogeneity progression. In contrast, low Vt MV prevents regional strain and heterogeneity progression in injured lungs.

Project description:BackgroundIn the Protective Ventilation in Cardiac Surgery (PROVECS) randomized, controlled trial, an open-lung ventilation strategy did not improve postoperative respiratory outcomes after on-pump cardiac surgery. In this prespecified subanalysis, the authors aimed to assess the regional distribution of ventilation and plasma biomarkers of lung epithelial and endothelial injury produced by that strategy.MethodsPerioperative open-lung ventilation consisted of recruitment maneuvers, positive end-expiratory pressure (PEEP) = 8 cm H2O, and low-tidal volume ventilation including during cardiopulmonary bypass. Control ventilation strategy was a low-PEEP (2 cm H2O) low-tidal volume approach. Electrical impedance tomography was used serially throughout the perioperative period (n = 56) to compute the dorsal fraction of ventilation (defined as the ratio of dorsal tidal impedance variation to global tidal impedance variation). Lung injury was assessed serially using biomarkers of epithelial (soluble form of the receptor for advanced glycation end-products, sRAGE) and endothelial (angiopoietin-2) lung injury (n = 30).ResultsEighty-six patients (age = 64 ± 12 yr; EuroSCORE II = 1.65 ± 1.57%) undergoing elective on-pump cardiac surgery were studied. Induction of general anesthesia was associated with ventral redistribution of tidal volumes and higher dorsal fraction of ventilation in the open-lung than the control strategy (0.38 ± 0.07 vs. 0.30 ± 0.10; P = 0.004). No effect of the open-lung strategy on the dorsal fraction of ventilation was noted at the end of surgery after median sternotomy closure (open-lung = 0.37 ± 0.09 vs. control = 0.34 ± 0.11; P = 0.743) or in extubated patients at postoperative day 2 (open-lung = 0.63 ± 0.18 vs. control = 0.59 ± 0.11; P > 0.999). Open-lung ventilation was associated with increased intraoperative plasma sRAGE (7,677 ± 3,097 pg/ml vs. 6,125 ± 1,400 pg/ml; P = 0.037) and had no effect on angiopoietin-2 (P > 0.999).ConclusionsIn cardiac surgery patients, open-lung ventilation provided larger dorsal lung ventilation early during surgery without a maintained benefit as compared with controls at the end of surgery and postoperative day 2 and was associated with higher intraoperative plasma concentration of sRAGE suggesting lung overdistension.Editor’s perspective

Project description:Rationale: In patients who are mechanically ventilated, diaphragm thinning on ultrasound is thought to correlate with diaphragm atrophy and has been associated with prolonged intubation. Factors other than atrophy, however, may cause changes in diaphragm thickness, which may confound studies examining changes in diaphragm thickness over time. Objectives: To determine if changes in the mode of mechanical ventilation or an interruption of sedatives have immediate effects on diaphragm thickness measurements in adult patients in the intensive care unit who are mechanically ventilated. Methods: Adult patients receiving invasive mechanical ventilation for less than 48 hours were included. Diaphragm thickness was measured at end-expiration and peak inspiration using ultrasound while patients were receiving both volume assist-control and pressure-support modes in a randomized crossover fashion. In patients receiving sedatives, additional measurements were taken after an interruption of sedatives. Measurements were compared between modes and on assist-control before and after an interruption of sedatives. Results: Of 85 patients enrolled, 66 had measurements on assist-control and spontaneous modes, and 40 had measurements before and after an interruption of sedatives. End-expiratory diaphragm thickness increased by a median of 0.08 mm after an interruption of sedatives (95% confidence interval [CI], 0.002 mm to 0.164 mm; P = 0.017), corresponding to a median increase of 6.5%. No difference was seen when comparing measurements taken on volume assist-control and pressure support (median difference, 0 mm; 95% CI, -0.07 mm to 0.08 mm; P = 0.98). Conclusions: End-expiratory diaphragm thickness increased by 6.5% after an interruption of sedatives. The effect of sedatives on measured diaphragm thickness should be considered in future studies examining changes in diaphragm thickness over time. Clinical trial registered with Clinicaltrials.gov (NCT04319939).

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Regional distribution of acoustic-based lung vibration as a function of mechanical ventilation mode.

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Regional distribution of acoustic-based lung vibration as a function of mechanical ventilation mode.

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