Comparison of plethysmographic and helium dilution lung volumes in patients with a giant emphysematous bulla as selection criteria for endobronchial valve implant

OBJECTIVES: To assess whether the difference in lung volume measured with plethysmography and with the helium dilution technique could differentiate an open from a closed bulla in patients with a giant emphysematous bulla and could be used as a selection criterion for the positioning of an endobronchial valve. METHODS: We reviewed the data of 27 consecutive patients with a giant emphysematous bulla undergoing treatment with an endobronchial valve. In addition to standard functional and radiological examinations, total lung capacity and residual volume were measured with the plethysmographic and helium dilution technique. We divided the patients into 2 groups, the collapse or the no-collapse group, depending on whether the bulla collapsed or not after the valves were put in position. We statistically evaluated the intergroup differences in lung volume and outcome. RESULTS: In the no-collapse group (n = 6), the baseline plethysmographic values were significantly higher than the helium dilution volumes, including total lung capacity (188 +/- 14 vs 145 +/- 13, P = 0.0007) and residual volume (156 +/- 156 vs 115 +/- 15, P = 0.001). In the collapse group, there was no significant difference in lung volumes measured with the 2 methods. A difference in total lung capacity of <= 13% and in residual volume of <= 25% measured with the 2 methods predicted the collapse of the bulla with a success rate of 83% and 84%, respectively. Only the collapse group showed significant improvement in functional data. CONCLUSIONS: Similar values in lung volumes measured with the 2 methods support the hypothesis that the bulla communicates with the airway (open bulla) and thus is likely to collapse when the endobronchial valve is implanted. Further studies are needed to validate our model.