A comparison of spirometry performed with two different methods

<bold>Background:</bold> Spirometry is the most common test that measures pulmonary function, and the primary outcomes are Forced Vital Capacity (FVC) and Forced Expiratory Volume in 1 second (FEV1). Different types of equipment are used, and manufacturers must ensure that all spirometers meet the ATS/ERS standards. It is known that the Digital Volume Transducer (DVT) method can provide lower forced spirometry values than the pneumotach method, but the values should be in the repeatable range of ±150 ml. <bold>Aim:</bold> To compare two different methods for spirometry <bold>Methods:</bold> In this retrospective study, 62 in-patients (39 % female, age 58 (13) years) referred to pulmonary rehabilitation, performed spirometry with two different methods. For diagnostic purpose spirometry was performed with pneumotach. Prior to the cardiopulmonary exercise test (CPET), spirometry was performed with DVT. Results as mean (SD): Spirometry performed with pneumotach; FVC 3,52 (1,08) L, FEV1 2,29 (1,01) L, with DVT; FVC 3,09 (1,05), FEV1 2,10 (0,95). Paired samples t-test showed significant difference (p<0,001) between the two methods, both in FVC and FEV1. The difference in volume between the two methods was FVC: 430 mL (395) and FEV1:187 mL (238). 87% of the patients had differences > 150 ml between the two methods, in FEV1 and/or FVC. <bold>Conclusion:</bold> We found a clinically and a statistically significant difference between the pneumotach and the DVT. In our laboratory we find it reasonable to follow the manufacturer’s recommendation to perform diagnostic spirometry with pneumotach and only use the DVT to provide a reference flow-volume loop when performing expiratory flow-volume loop (EFVL) during CPET.