Breath-by-breath fluctuations of pulmonary gas exchange and ventilation in COPD patients.

The purpose of the study was to characterise statistically the inherent fluctuations in breath-by-breath measurements of pulmonary gas exchange (oxygen uptake and carbon dioxide output, V*O2 and V*CO2, respectively) and pulmonary ventilation (V*E) in patients with chronic obstructive pulmonary disease (COPD) and to compare them with those of healthy control subjects. Thirty subjects with COPD [mean (SD): 67 (6) years old; forced expiratory volume in 1 min, FEV1 1.25( 0.