Novel spirometric parameters and small airway disease in COPD

<bold>Background:</bold> Chronic obstructive pulmonary disease (COPD) is characterised by progressive small airway disease (SAD), resulting in increased small airway resistance and gas trapping. Spirometric SAD is measured as the flow during the middle portion of the test (FEF_25%-75%). Characteristics of the flow-volume loop (FVL) can also be calculated, such as size or shape, that may have a role in assessing SAD. <bold>Aim:</bold> To compare alternative spirometric parameters with FEF_25%-75% for markers of SAD in COPD. <bold>Methods:</bold> Spirometry data from 111 patients with COPD (GOLD 1-4) was assessed. Alternative parameters assessed the size (area, AFV%) and shape (area of obstruction, Ao%AR) of the FVL. We propose novel parameters that assess the mid (3rd and 4th quartile area, AFV_Q3+Q4%) and end (volume exhaled between 0.5 and 0.1 L/s, Vf_0.1-0.5%FVC) regions of the FVL. Associations with small airway resistance (R₅-R₂₀) and gas trapping (residual volume/total lung capacity, RV/TLC) were performed using spearman rho, with p <0.05 considered significant. <bold>Results:</bold> 87 and 82 patients had R₅-R₂₀ and RV/TLC data, respectively. Results are shown in table 1. All parameters were moderately associated with small airway resistance, other than a weak association for Vf_0.1-0.5%FVC. All parameters showed a good association with gas trapping. R₅-R₂₀ and RV/TLC were associated (rho = 0.38, p <0.05). <bold>Conclusion:</bold> AFV% and Ao%AR performed best in relation to small airway resistance and gas trapping. These have potential for assessment of SAD. Table 1. Associations with small airway resistance and gas trapping (all p <0.05). <table-wrap><object-id>erj;64/suppl_68/PA3951/T1</object-id><object-id>T1</object-id><object-id>t1</object-id><table><colgroup><col></col><col></col><col></col></colgroup><tbody><tr><td>Parameter</td><td>R₅-R₂₀</td><td>RV/TLC</td></tr><tr><td>rho</td><td>rho</td></tr><tr><td>FEV₁%</td><td>−0.49</td><td>−0.61</td></tr><tr><td>FEF_25%-75%%</td><td>−0.41</td><td>−0.61</td></tr><tr><td>AFV%</td><td>−0.51</td><td>−0.71</td></tr><tr><td>Ao%AR</td><td>0.53</td><td>0.71</td></tr><tr><td>AFV_Q3+Q4%</td><td>−0.46</td><td>−0.65</td></tr><tr><td>Vf_0.1-0.5%FVC</td><td>0.32</td><td>0.56</td></tr></tbody></table></table-wrap>