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Objective:
Assess for any correlation between High Resolution Computed Tomography (HRCT) of the chest and Pulmonary Function Tests (PFT) in a unique patient population of active duty military personnel with post-COVID dyspnea. Initial evaluation is to assess for correlation between total lung capacity and residual volumes. The on-going evaluation is to assess whether CT findings of air trapping, ground glass opacification, and/or other findings correlate with PFT findings of obstruction or restriction. CT Densitometry was also performed to assess for a quantitative correlation between lung densities and PFT results.

Materials and Methods:
Active duty military personnel who were at least 3-6 month post COVID-19 infection were recruited for the study. As of this writing there are 144 patients enrolled with 86 of these patient meeting the inclusion criteria based on CT and PFT quality control parameters. Participants underwent a HRCT chest which included inspiratory, expiratory, prone, and supine acquisitions. Post-processing using Terrarecon was performed on the HRCT inspiratory and expiratory sequences which segmented the lungs using an automated algorithm and calculated volumes and densitometry. A qualitative assessment of air trapping was also performed. The participants also performed PFTs using spirometry, plethysmography, and bronchodilator responsiveness. These results were compared to assess for correlation and statistical significance using Pearson’s correlations.

Results:
Analysis of lung volume between HRCT and PFT in this unique patient population of 144 subjects had a correlation of 0.73 (<em>P</em> < 0.001). Due to limitations in CT techniques varying from institution and scanner protocols only 86 studies were deemed fit for analysis of the expiratory phase sequences. The lung volume correlation in this subset of 86 patients was 0.74 (<em>P</em> < 0.001) for TLC and 0.51 (<em>P</em> < 0.001) for RV. CT inspiratory volume was 1.4 L (17%) lower than TLC on PFT on average. Densitometry has been performed on all 144 subjects on the inspiratory and expiratory lung series at this point and statistical analysis is currently in progress using the 86 patients who met inclusion criteria based on scan quality parameters.

Conclusion:
Comparison between PFT and HRCT lung volumes in this unique patient cohort of military personnel with post-COVID dyspnea demonstrated lung volume correlation that is similar to other studies performed previously on patients with chronic pulmonary diseases as well as and healthy volunteers. This further validates HRCT as an accurate method of assessing TLC and its utility in preoperative planning and pulmonary disease evaluation and surveillance. Ongoing analysis is being performed to using densitometry on inspiratory and expiratory HRCT series to identify the qualitative and quantitative degree of air trapping. This data will then be used to assess for any potential correlation between PFT findings of restriction and/or obstruction and CT qualitative and quantitative findings of air trapping which might lead to more accurate diagnoses and prognostication in the future.