165 participants (100 chronic obstructive lung disease patients (COPD), 30 bronchial asthma patients (BA), and 35 healthy subjects) were examined. This study has aim to investigate possibilities of diagnosis gas exchange abnormalities in COPD patients with the use of capnometry. Capnometry allows to assess such ventilation and gas exchange abnormalities in stage III and IV COPD patients: decrease carbon dioxide production and its elimination impairment; decrease oxygen consumption, increase rest minute lung volume ventilation; tachypnoe and total duration of the respiratory cycle reduction; increase the "dead" space volume and its fraction in the tidal volume.