A pilot comparison of helium dilution and plethysmographic lung volumes to assess the impact of a long-acting bronchodilator on lung hyperinflation in COPD

BackgroundCurrently, two methods for measuring TLC, RV, and FRC are used in clinical pulmonary function laboratories: body plethysmography and helium dilution. However, these methods are not interchangeable. In moderate-to-severe airflow obstruction, dilution method tends to underestimate and body plethysmography tends to overestimate RV.PurposeIn 21 patients suffering from COPD (basal FEV1: 56.69 ± 13.64), we investigated whether the two methods of measuring FRC and RV could respond differently to a 2-week treatment with tiotropium 18 μg/day.Main resultsTiotropium induced a significant increase in FEV1 and FVC but not in IC. At baseline, FRCpleth, RVpleth and TLCpleth were higher than FRCHe, RVHe and TLCHe. At the end of the study FRCpleth, RVpleth and TLCpleth decreased and FRCHe, RVHe and TLCHe increased but only changes in FRCpleth and RVpleth were statistically significant.ConclusionThe use of body plethysmography seems to be more appropriate in clinical trials aimed at assessing the impact of a therapeutic procedure in patients with COPD and lung hyperinflation.