Sublingual positioning of a silicon capillary system is applied. After 15 min, while the individual is in resting position with closed mouth and normal tidal breathing through the nose is performed, the silicon capillary system is connected to a capnometer and CO2 tension is measured.

The investigators hypothesis is that this setup offers a non-invasive assessment of ventilatory efficiency with similar accuracy as arterial PCO2.

We have developed a new silicon capillary system for sublingual monitoring of CO2 tension in order to assess tissue perfusion. This set up is non-invasive, cheaper than previous tonometry devices and easier to apply in clinical routine. We have recruited patients with stable COPD and healthy individuals.

Sublingual tonometry results were evaluated after 15 min of tidal breathing with a capnometer for CO2 tension. Corresponding end tidal CO2 (PETCO2)and arterial blood gas values (pH, PaCO2, PaCO2) were also investigated.

Inclusion Criteria:

• COPD patients with stable disease

Exclusion Criteria:

• acute exacerbation of COPD