Changes in pCO₂ levels during 6-minute walking test in patients with very severe COPD

Abstract

Background

Current literature provides only scarce information on the development of carbon dioxide pressure (pCO₂) in patients with COPD during physical activities. Therefore aim of this study was to investigate pCO₂ levels during exercise (6-minute walking test; 6MWT) and at night rest in patients with very severe COPD.

Methods

75 COPD patients (age: 63±8y, FEV₁: 33±9 % pred.) participated in this prospective study. PCO₂ was transcutaneously measured by the Sentec^® device during a 6MWT and during one night. These measurements where repeated after 1 week and mean values were used for analyses. Peak pCO₂ during 6MWT was the primary outcome parameter.

Results

Patients increased their pCO₂ level by 3.4±3.7 mmHg to a peak value of 43.6±6.5 mmHg during the 6MWT. A higher pCO₂ during the 6MWT correlated slightly with higher perceived dyspnoe (r=0.32, p<0.05). It seems to be more likely that a higher pCO₂ level during the 6MWT occurs in patients that are younger (correlation with age: r=-0.34, p<0.001) and who suffer from more airflow limitation (correlation with FEV₁: r=-0.28, p<0.05). Additionally there was a positive correlation (r=0.63, p<0.0001) between the peak pCO₂ values measured at night and during 6MWT. In 36% of the patients pCO₂ level increased more than 5mmHg. This group of pCO₂-increasers reached a level of 47.4 mmHg at the end of 6MWT.

Conclusions

In general the increase of pCO₂ in patients with very severe COPD during 6MWT seems to be slight and not to cause relevant clinical symptoms. However, younger patients with more advanced airflow limitation may need special attention with regard to hypercapnia.