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

BACKGROUND: Currently, 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. PURPOSE: In 21 patients suffering from COPD (basal FEV(1): 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 microg/day. MAIN RESULTS: Tiotropium induced a significant increase in FEV(1) and FVC but not in IC. At baseline, FRC(pleth), RV(pleth) and TLC(pleth) were higher than FRC(He), RV(He) and TLC(He). At the end of the study FRC(pleth), RV(pleth) and TLC(pleth) decreased and FRC(He), RV(He) and TLC(He) increased but only changes in FRC(pleth) and RV(pleth) were statistically significant. CONCLUSION: The 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.