Reproducibility of airway luminal size in asthma measured by HRCT

Abstract

Brown RH, Henderson RJ, Sugar EA, Holbrook JT, Wise RA, on behalf of the American Lung Association Airways Clinical Research Centers. Reproducibility of airway luminal size in asthma measured by HRCT. J Appl Physiol 123: 876-883, 2017. First published July 13, 2017; doi:10.1152/japplphysiol.00307.2017.-High-resolution CT (HRCT) is a well-established imaging technology used to measure lung and airway morphology in vivo. However, there is a surprising lack of studies examining HRCT reproducibility. The CPAP Trial was a multicenter, randomized, three-parallel-arm, sham-controlled 12-wk clinical trial to assess the use of a nocturnal continuous positive airway pressure (CPAP) device on airway reactivity to methacholine. The lack of a treatment effect of CPAP on clinical or HRCT measures provided an opportunity for the current analysis. We assessed the reproducibility of HRCT imaging over 12 wk. Intraclass correlation coefficients (ICCs) were calculated for individual airway segments, individual lung lobes, both lungs, and air trapping. The ICC [95% confidence interval (CI)] for airway luminal size at total lung capacity ranged from 0.95 (0.91, 0.97) to 0.47 (0.27, 0.69). The ICC (95% CI) for airway luminal size at functional residual capacity ranged from 0.91 (0.85, 0.95) to 0.32 (0.11, 0.65). The ICC measurements for airway distensibility index and wall thickness were lower, ranging from poor (0.08) to moderate (0.63) agreement. The ICC for air trapping at functional residual capacity was 0.89 (0.81, 0.94) and varied only modestly by lobe from 0.76 (0.61, 0.87) to 0.95 (0.92, 0.97). In stable well-controlled asthmatic subjects, it is possible to reproducibly image unstimulated airway luminal areas over time, by region, and by size at total lung capacity throughout the lungs. Therefore, any changes in luminal size on repeat CT imaging are more likely due to changes in disease state and less likely due to normal variability.NEW & NOTEWORTHY There is a surprising lack of studies examining the reproducibility of high-resolution CT in asthma. The current study examined reproducibility of airway measurements. In stable well-controlled asthmatic subjects, it is possible to reproducibly image airway luminal areas over time, by region, and by size at total lung capacity throughout the lungs. Therefore, any changes in luminal size on repeat CT imaging are more likely due to changes in disease state and less likely due to normal variability.

Keywords: asthma; computer tomography; precision.

Fig. 1.

Box-and-whisker plot of luminal airway diameter (mm) at functional residual capacity (FRC) by lung segment at the first visit in the 6 airway segments that were measured across all subjects at both time points. Airway segments included the bronchus intermedius segment (BronInt), left lower bronchus number 6 segment (LLB6), left middle lobe segment (LMB), left upper lobe segment (LUL), right middle lobe segment (RMB), and right upper lobe segment (RUL).

Fig. 2.

Bland-Altman plot showing average of the 2 luminal area measures (mm²) of each of the 258 airways among the 6 airway segments for all the subjects vs. the difference in the 2 size measures (mm²) of each airway at total lung capacity (TLC). △,  BronInt; ○, LLB6; ◇, LMB; ×, LUL; □, RMB; ☆, RUL. Note excellent reproducibility at TLC.

Fig. 3.

Bland-Altman plot showing average of the 2 airway wall areas (as a fraction of total airway area) of each of the 258 airways among the 6 airway segments for all the subjects vs. the difference in the 2 airway wall areas (as a fraction of total airway area) of each airway at TLC. △,  BronInt; ○, LLB6; ◇, LMB; ×, LUL; □, RMB; ☆, RUL. Note modest reproducibility.