Summary:“First real-time imaging of bronchoscopic lung volume reduction by electrical impedance tomography”
Abstract Summary: This study investigated the real-time effects of inspired oxygen fraction (FIO₂) on regional lung volumes and ventilation/perfusion during bronchoscopic lung volume reduction (BLVR) using endobronchial valves (EBVs), utilizing electrical impedance tomography (EIT). The findings demonstrate that higher FIO₂ significantly accelerates and amplifies atelectasis, leading to faster lung volume reduction. EIT provided precise real-time monitoring, capturing immediate shifts in lung volumes, ventilation, and perfusion, offering critical insights for clinical decision-making during BLVR procedures.
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Computed tomography images. Computed tomography (CT) images from both occlusion methods and fraction of inspired oxygen (FIO2). Time points were Pre (under the standard mechanical ventilation settings) and T15 (15-minute occlusion). The Pre vs. T15 CT images were unequivocally different with FIO2 1.0. In addition, the T15 CT images with FIO2 1.0 were also clearly different between the two occlusion methods. The FIO2 1.0 resulted in complete atelectasis with the balloon and partial atelectasis with the valves. The images at T15 with FIO2 1.0 also show a visible expansion of the accessory lobe displaced towards the left hemithorax (white arrow), which was more prominent in the Balloon Occlusion Method
Key Points:
Purpose and Clinical Context: Bronchoscopic lung volume reduction (BLVR) with endobronchial valves (EBVs) is used to treat emphysema by reducing hyperinflation. Complete lobe atelectasis is crucial for its success, particularly in patients lacking collateral ventilation (CV-).
Study Objective: The study aimed to evaluate, in real-time, how different oxygen concentrations (FIO₂ 0.5 vs. 1.0) affect lung volume reduction and ventilation/perfusion dynamics during BLVR procedures, employing electrical impedance tomography (EIT).
Methodology: An animal study involved six anesthetized piglets subjected to lower lobe occlusion by balloon catheter and EBVs at two different FIO₂ levels (0.5 and 1.0). EIT measured real-time lung volumes (EELI), ventilation changes (TIV), and perfusion shifts, alongside computed tomography (CT) and local pocket pressures.
Impact of High FIO₂ on Lung Volume Reduction: Under high FIO₂ (1.0), there was a rapid and substantial reduction in lung volumes compared to lower FIO₂ (0.5), suggesting accelerated atelectasis due to faster oxygen absorption after airway occlusion.
Real-time EIT Monitoring: EIT effectively captured immediate regional lung changes, providing a dynamic, continuous, and accurate method to observe real-time lung volume, ventilation, and perfusion changes during BLVR.
Comparison with CT Imaging: Simultaneous CT and EIT data from one animal confirmed the EIT findings, with high FIO₂ causing more pronounced atelectasis and substantial lung volume reduction, validating EIT’s accuracy and reliability.
Local Pocket Pressure Dynamics: Local pocket pressures measured distal to occlusion mirrored EIT results, showing rapid pressure drops (including negative pressures) with higher FIO₂, reflecting significant interdependence forces and tissue strain.
Clinical Implications – Pneumothorax Risk: Rapid atelectasis triggered by higher FIO₂ could elevate the risk of pneumothorax due to increased local lung strain. However, real-time EIT monitoring can detect early signs of pneumothorax, potentially improving safety and clinical management.
Human Case Illustrations: Two clinical cases demonstrated practical EIT application, highlighting its ability to detect real-time changes associated with collateral ventilation assessment and to promptly diagnose complications such as pneumothorax during BLVR procedures.
Future Research Directions: The authors advocate for future clinical studies to validate real-time EIT application in diverse patient populations, refine intra-procedural decision-making, and enhance personalized strategies to optimize BLVR outcomes.
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Perfusion distributions. Electrical impedance tomography (EIT) and dynamic contrast-enhanced computed tomography (CT) perfusion distributions with Balloon (A) and Valves (B) under fraction of inspired oxygen 1.0. Pre (under the standard mechanical ventilation settings) and T15 (15-minute occlusion). The EIT and CT images were sub-segmented into two regions-of-interest (ROIs): right and left hemithoraces. Both imaging techniques showed a decreased perfusion in the left ROI at T15
Conclusion: Electrical impedance tomography successfully demonstrated in real-time that higher oxygen concentrations significantly accelerate lung volume reduction during BLVR, providing a robust tool for monitoring regional lung dynamics. EIT can enhance procedural decision-making, early detection of complications, and overall safety during bronchoscopic interventions.
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Observations from the second patient. A 71-year-old male with emphysema underwent a left single lung transplant seven years before. He developed progressive disabling dyspnea starting five years after transplantation, mainly because of progressive hyperinflation of the native lung. The forced expiratory volume in one second (FEV1) dropped from 1860 mL to 580 mL, and the post-transplant Modified Medical Research Council (mMRC) dyspnea scale shifted from 1 to 3 within the last year when he became full-time oxygen-dependent because of bronchiolitis obliterans and severe hyperinflation of the native lung. The observations from this patient focused on the periods before (briefly after sedation: Pre), during, and after bronchoscopic lung volume reduction (BLVR) with one-way endobronchial valves (EBV)-ZephyrTM (See Supplementary Video S1, Additional File 5). Electrical impedance tomography (EIT) continuous real-time imaging showed the changes in regional ventilation, and changes in regional end-expiratory lung impedance (EELI). The EIT images were sub-segmented into two regions-of-interest (ROIs): right (orange) and left (blue) hemithorax. A ChartisTM catheter was advanced into the right lower lobe bronchus, and a negative collateral ventilation (CV-) pattern was recorded by the ChartisTM console. Three EBV ZephyrTM valves were placed in the right lower lobe segmental bronchi. Upon completion of the BLVR procedure following the withdrawal of the laryngeal mask during recovery from the sedation, with the patient still in the operating room, he had a sudden coughing spell followed immediately by dyspnea, right-sided chest pain, and a steep decrease in peripheral capillary oxygen saturation (SpO2), from 98 to 80%. Immediately before the sudden coughing spell (See Supplementary Video S1, Additional File 5), the EIT tracings showed a quick rise in the regional EELI of the right hemithorax (orange EIT tracing), combined with a corresponding significant attenuation of the regional ventilation within the same right ROI (A), which are the typical changes of a pneumothorax in the EIT signals [23]. As the patient?s respiratory condition rapidly deteriorated, becoming critical, in addition to the accompanying real-time EIT tracings and images for pneumothorax altogether, allowed us to proceed with an emergency right-sided chest tube drainage. It was followed by improved dyspnea and pain, yielding stabilization of the ventilatory condition and SpO2 within a few minutes. (A) shows the EIT tracings and images of the events before (briefly after sedation: Pre), during each valve placement, and throughout the pneumothorax event, including post-drainage (See Supplementary Video S1, Additional File 5). The patient recovered in the operating room, and the air leak from the chest tube resolved gradually until its removal on the fifth day after the drainage procedure. Three months after the BLVR procedure, SpO2 increased from 89.6 to 93%, the FEV1 and the forced vital capacity (FVC) showed an increase of 130 mL and 250 mL, respectively. The dyspnea scale dropped from mMRC 3 to 2.(B): Chest radiograph and computed tomography scan of this patient showed in the upper panel (before BLVR) the hyperinflated right lung, primarily due to the right lower lobe displacing the mediastinum towards the left side. In the lower panel (three months after BLVR), the right lower lobe atelectasis with the endobronchial valves in place (arrow) and the mediastinal shifted towards the midline
First real-time imaging of bronchoscopic lung volume reduction by electrical impedance tomography
Watch the following video on “Exploring V/Q with Electrical Impedance Tomography – Prof Marcelo Amato” by Timpel Medical
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