Relationship between quantitative CT metrics and health status and BODE in chronic obstructive pulmonary disease

Abstract

Background: The value of quantitative CT (QCT) to identify chronic obstructive pulmonary disease (COPD) phenotypes is increasingly appreciated. The authors hypothesised that QCT-defined emphysema and airway abnormalities relate to St George's Respiratory Questionnaire (SGRQ) and Body-Mass Index, Airflow Obstruction, Dyspnea and Exercise Capacity Index (BODE).

Methods: 1200 COPDGene subjects meeting Global Initiative for Chronic Obstructive Lung Disease (GOLD) criteria for COPD with QCT analysis were included. Total lung emphysema was measured using the density mask technique with a -950 Hounsfield unit threshold. An automated programme measured mean wall thickness (WT), wall area percentage (WA%) and 10 mm lumenal perimeter (pi10) in six segmental bronchi. Separate multivariate analyses examined the relative influence of airway measures and emphysema on SGRQ and BODE.

Results: In separate models predicting SGRQ score, a 1 unit SD increase in each airway measure predicted higher SGRQ scores (for WT, 1.90 points higher, p=0.002; for WA%, 1.52 points higher, p=0.02; for pi10, 2.83 points higher p<0.001). The comparable increase in SGRQ for a 1 unit SD increase in emphysema percentage in these models was relatively weaker, significant only in the pi10 model (for emphysema percentage, 1.45 points higher, p=0.01). In separate models predicting BODE, a 1 unit SD increase in each airway measure predicted higher BODE scores (for WT, 1.07-fold increase, p<0.001; for WA%, 1.20-fold increase, p<0.001; for pi10, 1.16-fold increase, p<0.001). In these models, emphysema more strongly influenced BODE (range 1.24-1.26-fold increase, p<0.001).

Conclusion: Emphysema and airway disease both relate to clinically important parameters. The relative influence of airway disease is greater for SGRQ; the relative influence of emphysema is greater for BODE.

Figure 1

Frequency distribution of BODE index scores (left panel) and St. George's Respiratory Questionnaire (SGRQ) total scores (right panel).

Figure 2

Figure 2A. Three dimensional plot demonstrating the relationship between increasing pi10, emphysema % and St. George's Respiratory Questionnaire score (left upper panel). Figure 2B. Density plot of COPD subjects with SGRQ score approximately 90^th percentile (score ≥ 64, n=146) demonstrating degree of pi10 and emphysema in this subgroup. Percent of subjects displayed at right, high density in red, low density in blue (right upper panel). Figure 2C. Three dimensional plot demonstrating the relationship between increasing pi10, emphysema% and BODE index score (left lower panel). Figure 2D. Density plot of COPD subjects with BODE score approximately 90^th percentile (score ≥ 6, n=142) demonstrating the degree of pi10 and emphysema in this subgroup. Percent of subjects displayed at right, high density in red, low density in blue (right lower panel).