Quantitative imaging analysis detects subtle airway abnormalities in symptomatic military deployers

Abstract

Background Exposure to inhalational hazards during post-9/11 deployment to Southwest Asia and Afghanistan puts military personnel at risk for respiratory symptoms and disease. Pulmonary function and qualitative chest high resolution computed tomography (HRCT) are often normal in “deployers” with persistent respiratory symptoms. We explored the utility of quantitative HRCT imaging markers of large and small airways abnormalities, including airway wall thickness, emphysema, and air trapping, in symptomatic deployers with clinically-confirmed lung disease compared to controls. Methods Chest HRCT images from 45 healthy controls and 82 symptomatic deployers with asthma, distal lung disease or both were analyzed using Thirona Lung quantification software to calculate airway wall thickness (by Pi10), emphysema (by percentage of lung volume with attenuation < -950 Hounsfield units [LAA%-950]), and three parameters of air trapping (expiratory/inspiratory total lung volume and mean lung density ratios, and LAA%-856). SAS v.9.4 was used to compare demographic and clinical characteristics between deployers and controls using Chi-Square, Fisher Exact or t-tests. Linear regression was used to assess relationships between pulmonary function and quantitative imaging findings. Results Gender and smoking status were not statistically significantly different between groups, but deployers were significantly younger than controls (42 vs 58 years, p < 0.0001), had higher body mass index (31 vs 28 kg/m2, p = 0.01), and had fewer total smoking pack-years (8 vs. 26, p = 0.007). Spirometric measures were not statistically significantly different between groups. Pi10 and LAA%-950 were significantly elevated in deployers compared to controls in unadjusted analyses, with the emphysema measure remaining significantly higher in deployers after adjustment for age, sex, smoking, BMI, and expiratory total lung volume. Air trapping parameters were more common in control images, likely due to differences in age and smoking between groups. Among deployers, LAA%-950 and Pi10 were significantly correlated with spirometric markers of obstruction based on ratio of forced expiratory volume in one second (FEV1)/forced vital capacity (FVC) and/or percent predicted FEV1. Conclusions Quantitative chest HRCT imaging analysis identifies emphysema in deployers with asthma and distal lung disease, and may be useful in detecting and monitoring deployment-related lung disease in a population where spirometry is typically normal.

Consensus Statements on Deployment-Related Respiratory Disease, Inclusive of Constrictive Bronchiolitis

“… 25 These techniques have shown promise in identifying associations with occupational exposures, 26 but only recently have been investigated in previously deployed individuals with respiratory symptoms. 27 , 28 , 29 Although specialty centers are most prepared to perform high-resolution CT scan image acquisition, quantitative analysis, and specialist interpretation, it may be feasible to explore developing and implementing a high-resolution CT scan scanning protocol at standard facilities and centralized quantitative analysis within an integrated health network such as the US Department of Veterans Affairs health-care system.…”

Findings on High Resolution Computed Tomography in Symptomatic Veterans with Deployment-Related Lung Disease

“…In conclusion, given the limitations of HRCT visual assessment for detection of DDLD observed in this cohort, along with cost and radiation dose, alternative approaches to diagnosis may be needed. Techniques such as quantitative image analysis of airway wall thickening and emphysema 37 and functional lung imaging for ventilation inhomogeneity 38 may be more sensitive than visual assessment of HRCT in detecting distal airways abnormalities. Other modalities such as lung clearance index testing, separately or in combination with quantitative image analysis, may enhance diagnostic sensitivity 39 and await further investigation.…”

Deployment-Related Respiratory Disease: Where Are We?

“…49 50 Another diagnostic tool that has been evaluated among military deployers is impulse oscillometry (iOS), which is commercially available and may be especially useful for patients that have trouble performing forced maneuvers. 51 Quantitative imaging parameters of emphysema, air trapping, and airway wall thickening can identify subtle abnormalities that may be useful in noninvasive diagnosis of DRRD 52 and are available commercially. 53 54 Davis et al used a technique called parametric response mapping (PRM) to assess degrees of functional small airways disease (fSAD) in military personnel with constrictive bronchiolitis (MPCB), a second group with COPD, and a control group of asymptomatic smokers.…”