Obstruction Grade and Preserved Lung Function assessed with Ventilation/Perfusion SPECT and its association with Lung Function in COPD and healthy smokers

Ventilation/Perfusion (V/P) Single-Photon Emission Computed Tomography (SPECT) is informative in early diagnosis and grading of chronic obstructive pulmonary disease (COPD) as shown earlier. We aimed to investigate the associations between comprehensive pulmonary function tests, symptoms, % preserved lung function (%PLF), and obstruction grade (OG) assessed with V/P SPECT. 53 patients with COPD and 16 healthy smoking /former smoking subjects with FEV1/FVC ≥0.7 completed the COPD Control Questionnaire (CCQ). They were examined with spirometry, body plethysmography, diffusion capacity test (DLCO), impulse oscillometry system (IOS) followed by V/P SPECT. %PLF was estimated semi-quantitively from images of ventilation and perfusion, and OG was estimated from the ventilation analyses (score0-3). We found readable obstruction grades in 15 healthy smoking individuals (OG1:n=7;OG2:n=7; OG3:n=1), despite normal spirometry. Moreover, %PLF correlated with symptoms (CCQ score: r=-0.55), airway obstruction (measured as FEV1/FVC; r=0.66), and diffusion capacity(r=0.74), p<0.0001 for all. Moreover, %PLF also correlated with total airway resistance (R5 as % of predicted; r= −0.46; p=0.048) and reactance (X5%pred, r= −0.47; p<0.0001). OG correlated with symptoms (r=0.50), airway obstruction (FEV1/FVC: r=-0.64), diffusion capacity (r=-0.65), total airway resistance (R5%pred; r=0.46) and reactance (X5%pred; r=0.42), p<0.0001 for all.V/P SPECT findings correlated significantly with the other lung function measurements, but the classification of obstruction grade in healthy smokers showed an obstruction not reflected by symptoms or other lung function measurements. This raises questions about the possible use of novel methods such as IOS in the early detection of obstruction as good as V/P SPECT.