We thank D. Stanescu for his interest in our paper 1 and for giving us the opportunity to clarify an important methodological issue. First of all, we would like it to be remembered that our document was intended for use in designing clinical trials on pharmacological treatments of chronic obstructive pulmonary disease. The point we wanted to make clear is that, because of the well known potential errors inherent to dilution methods and body plethysmography 2–4, they should not be used interchangeably within a clinical trial. We are aware that keeping the panting frequency below 1 Hz helps reduce overestimation of lung volumes measured by body plethysmography in the presence of airflow obstruction 5, 6, but this has to be confirmed in very severe chronic obstructive pulmonary disease and it may not be easily feasible in large multicentre clinical trials. Notwithstanding, we agree that, whenever possible, the plethysmographic method should be adopted, not only because it is less time consuming, but also because it allows assessment of repeatability of measurements within sessions and, thus, better quality control.
Statement of interest
Statements of interest for M. Cazzola and V. Brusasco can be found at www.erj.ersjournals.com/misc/statements.shtml
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