Functional Respiratory Imaging Offers Value in Cystic Fibrosis

Air trapping and pulmonary blood distribution were found to be clinically relevant functional respiratory imaging (FRI) parameters associated with spirometry and the 6-minute walk test (6MWT) in patients with cystic fibrosis (CF), suggesting these FRI variables could offer value in the assessment of functional characteristics of the CF respiratory system, according to research findings published in BMC Pulmonary Medicine.

The FRI modality comprises a combination of high-resolution computed tomography (CT) images and computational fluid dynamics to gain objective and quantitative insights into lung structure and function. While FRI has demonstrated value in chronic obstructive pulmonary disease and asthma, few studies have been conducted to demonstrate its utility in the assessment of CF.

To close this research gap, a team of Belgian investigators conducted a cross-sectional analysis of 39 chest CTs from 24 patients with CF (mean age, 24±9 years). At the time of their first CT scan, patients had a mean percentage predicted of forced expiratory volume in 1 second (ppFEV₁) of 71±25%.

The FRI outcomes assessed in this study were regional airway volume, airway wall volume, airway resistance, lobar volume, air trapping, and pulmonary blood distribution. The CF-CT score was used by 2 investigators to independently evaluate structural abnormalities on the CT scans. Patients also underwent spirometry and the 6MWT.

There were significant associations between the total CF-CT score per lung lobe and air trapping (r=0.43, P <.001), airway volume (r=0.35, P <.001), airway wall volume (r = 0.30, P <.001), and airway resistance (r=-0.15, P =.0495). Other significant associations were found between airway volume and percentage of bronchiectasis (r=0.40, P <.001), as well as between air trapping on FRI and percent of air trapping of the CF-CT score (r=0.38, P <.001). The investigators observed a negative correlation between total CF-CT score and BV5%, which represents the proportion of blood vessels with a cross-sectional area less than 5 mm² (P <.001).

In regression analyses, the researchers found a significant association between ppFEV₁ and FRI parameters of air trapping (r=-0.85, P <.001), lobar volume at FRC (r=-0.72, P <.001), BV10% (r=-0.57, P =.003), BV5_10% (the percentage of blood vessels between 5 and 10 mm²; r=- 0.61, P =.002), and BV5% (r=0.64, P <.001). Air trapping was the only variable significantly associated with the distance covered in the 6MWT, while oxygen saturation (SpO₂₎ at the end of the walking test was associated with air trapping, lobar volume at functional residual capacity (FRC), vessels between 5 and 10 mm², and BV5%.

A potential limitation of this study included the lack of controls without CF. Additionally, the researchers noted that additional investigation is needed to evaluate the association between longitudinal changes of FRI parameters and other relevant clinical outcomes.

“Nevertheless,” the researchers added, “the set of structural components of FRI providing quantitative, objective and regional information have the potential to complement results derived from conventional outcome measures in future CF research as an alternative to visual CT scores.”

Reference

Lauwers E, Snoeckx A, Ides K, et al. Functional respiratory imaging in relation to classical outcome measures in cystic fibrosis: a cross-sectional study. BMC Pulm Med. 2021;21(1):256. doi:10.1186/s12890-021-01622-3