Measuring Airway Compliance Of Pulmonary Fibrosis By Endobronchial Optical Coherence Elastography

Part 1:Establishing Clinically Applicable Endobronchial Optical Coherence ElastographyBackground:Optical Coherence Tomography（OCT）has been applied in the airway for more than 20 years.It is mostly used for structural imaging such as evaluating the morphology and structure of the airway,which has great application value in respiratory diseases.To enable endobronchial OCT（EB-OCT）to provide more information,recent researchers have used EB-OCT to detect the change of airway lumen area under different pressure to measure airway compliance,which named endobronchial optical coherence elastography（OCE）,expanded EB-OCT from structural imaging to functional imaging,which has a broad application prospect in respiratory diseases.However,it is rarely used in clinis,because of the problems of methodology such as unstable imaging and limited imaging sites.Objective:1)To establish a clinically applicable optical coherence elastography technique in the airway to explore the relevant factors affecting the assessment results of airway compliance;2)To explore the differences of airway compliance in normal people at different genertaions.Methods:Patients diagnosed with pulmonary nodules in Guangzhou Medical University of the First Affiliated Hospital from January 2022 to June 2023,aged older than 18 and younger than 70 years old,requiring endotracheal intubation under general anesthesia and undergoing bronchoscopy navigation guided lung biopsy were continuously included.1.Esophageal pressure monitoring equipment was inserted before surgery,and respiratory mechanics were used to monitor airway pressure and transpulmonary pressure;2.After endotracheal intubation,different levels of pressure are downward OCT scanned then injecting muscle relaxant drug and repeating the procedure of scanning when muscle relaxant drugs work.3.After the whole procedure,different generations of airway compliance were calculated,and the differences in airway compliance before and after the use of different respiratory mechanics and muscle relaxants were compared.4.Finally,an airway elastography schematic was generated and rendered by MAYA software.Results:A total of 4 patients with pulmonary nodules were enrolled,2 males and 2 females.1)All patients can stably detect that the lumen area of different stages increases with the increase of pressure,and the regression equation（R²=0.93）is fitted according to the change value of pressure area,and the regression coefficient is airway compliance,and the specific compliance is the luminal area at baseline pressure compared to the airway compliance.2)There was no significant difference between airway compliance and specific compliance at all generations between airway pressure and transpulmonary pressure assessment（p>0.05）,and no significant change in airway compliance and specific compliance at generations before and after muscle relaxation drugs（p>0.05）.3)The overall airway compliance of patients decreased with the increase of airway generation,and the airway compliance of generation 7 was higher than that of generation 6 but still less than that of generation 5,of which the airway compliance of generation 3 was greater than that of generation 7 airway without significant difference（p>0.05）;the overall airway specific compliance of patients increased with the increase of progression,and the specific compliance of generation 7 airway was significantly higher than that of generation 3 and 4（p<0.05）.4)Build a 3D model of the airway based on the OCT image and render the elastography schematic diagram according to the measured airway specific compliance.Conclusion:1)Establish endobronchial optical coherence elastography（EB-OCE）,which can detect the airway up to the 7^thairway;airway pressure is consistent with transpulmonary pressure assessment compliance;muscle relaxants have no significant effect on airway compliance.2)Distal airway is less than the proximal airway in airway compliance,but higher than the proximal airway in specific compliance;7^thairway is significantly higher than the 3^rdairway.Meaning:Expanding OCT imaging from structural imaging to functional imaging in airway;provide new technical means for clinical research on various respiratory diseases involving the airways.Part 2: Measuring Airway Compliance of Pulmonary Fibrosis by Endobronchial Optical Coherence ElastographyBackground:Pulmonary fibrosis is a life-limiting interstitial lung disease with abnormal deposition of fibers in the lung leading to the decline of lung diffusion function and compliance.There is a lack of early and accurate diagnostic means,and it is particularly important to understand its pathophysiology.In recent years,it has been found that small airway diseases are an important feature of pulmonary fibrosis.Small airway shrinkage and fibrosis have been observed in the early stage of pulmonary fibrosis,which is of great value for the pathogenesis research and early diagnosis of pulmonary fibrosis.Theoretically,small airway diseases,especially fibrosis,will affect its compliance,which has not been studied.Objective:Using EB-OCE technology to assess the difference in airway compliance between normal individuals and patients with pulmonary fibrosis,exploring potential clinical value.Methods:Patients diagnosed in Guangzhou Medical University of the First Affiliated Hospital from January 2022 to June 2023,aged over 18 and under 70 years old,who reported interstitial pulmonary disease with fibrosis and required TBCB operation by chest high-resolution CT were successively included.1.Divided into mild pulmonary fibrosis group and severe fibrosis group according to the degree of pulmonary fibrosis scoring.2.Preoperative esophageal pressure monitoring equipment was implanted to monitor airway pressure and transpulmonary pressure by respiratory mechanics.3.After endotracheal intubation,different levels of pressure were given through the ventilator,and OCT scanning was performed under different levels of pressure.4.Bronchial biopsies were performed at the 3rd and 7th airway in the lower lobe of the right lung after the scan.5.Airway compliance and specific compliance at different levels were calculated after the whole procedure.6.a-SMA and EVG staining were performed to quantitatively analyze the difference between airway smooth muscle and elastic fiber content in airway mucosa.Results:A total of 12 subjects were enrolled,4 were normal,and 8 patients with pulmonary fibrosis were grouped according to the degree of pulmonary fibrosis in the lower lobe of the right lung: 4 people with mild pulmonary fibrosis,1 male and 3 female;There were 4 people with severe pulmonary fibrosis,3 men and 1 woman.1)There were no significant differences in airway compliance and specific compliance between the mild pulmonary fibrosis group and the severe pulmonary fibrosis group（p>0.05）.2)Starting from 5th airway,the airway compliance of patients with mild pulmonary fibrosis group and the severe pulmonary fibrosis group is lower than normal group;In the 7th generation airway,the airway specific compliance of severe pulmonary fibrosis group was significantly lower than that of normal group（p<0.05）.3)FVC in lung function was correlated with the degree of fibrosis of the patient（r=-0.688,p<0.05）,and the specific compliance of 7th airway was more strongly correlated than FVC（r=-0.862,p<0.01）.4)The contents of elastic fiber and smooth muscle in 7th airway mucosa decreased with the aggravation of fibrosis degree between normal people and patients with different degrees of pulmonary fibrosis（P>0.05）.The content of smooth muscle in the airway of normal people was fairly significantly higher than that of patients with severe fibrosis（P=0.089）.Conclusion:1)The distal airway specific compliance of patients with pulmonary fibrosis is lower than that of normal people,especially in patients with severe pulmonary fibrosis,the specific compliance of the 7th airway is significantly lower than normal people.2)7^th airway specific compliance is more closely correlated with pulmonary fibrosis severity than FVC.Meaning:Provided new means and reference for assessing the severity,early diagnosis,and prognosis of pulmonary fibrosis.