Differences in gas exchange between severities of chronic obstructive pulmonary disease

Impaired ventilation on cardiopulmonary exercise test (CPET) is seen in patients with chronic obstructive pulmonary disease (COPD). However, evaluation of the differences of abnormal gas exchange in COPD according to GOLD severity criteria is limited. A retrospective review was performed on all COPD patients referred for CPET at our center between 1998 and 2010. There were 548 patients compared according to GOLD severity. GOLD groups were significantly different from each other in regards to pressure of end-tidal carbon dioxide (PETCO2) with progressively higher PETCO2 with increasing GOLD severity. Ratio of minute ventilation to carbon dioxide production (V˙E/V˙CO2) and exercise capacity as measured by and V˙O2 % and work rate in watts% was inversely proportional to GOLD severity. Breathing reserve, minute ventilation, and tidal volume at peak exercise were significantly decreased with increasing disease severity between GOLD groups. We concluded that gas exchange is distinctive among different GOLD severity groups; specifically, GOLD 3 and 4 have a significantly higher PETCO2 and a significantly lower V˙E/V˙CO2 than GOLD 2.

► The chief finding of this study is that there is altered gas exchange with exercise, as measured by V˙E/V˙CO2 and PETCO2, between patients with various severities of COPD. ► Patients with GOLD 3 and 4 COPD have a significantly higher PETCO2 and lower V˙E/V˙CO2 at peak exercise than GOLD 2 patients. ► We speculate that true physiology with exercise includes both lower PETCO2 and higher V˙E/V˙CO2 in GOLD 2 COPD, reflecting less efficient ventilation, and high PETCO2 and low V˙E/V˙CO2 in GOLD 3 and 4 COPD, reflecting ventilatory limitations. ► Our novel finding is that we demonstrate ventilatory changes over the spectrum of advanced COPD with complete ventilatory parameters on CPET.