Assessment of Continuous Measurement of Transcutaneous CO2 for Evaluation of Alveolar Dead Space During Exercise

The study aim is to monitor, during exercise tests carried out in various conditions, the alveolar dead space, by means of continuous transcutaneous measurement of Pt CO2, which would be used as a surrogate for arterial PaCO2. Validity of this measurement needs to be assessed against arterial sampling (either arterial, or arterialized capillary), especially with regards to the lag time required by the CO2 diffusion from the arterial compartment (PaCO2) to the cutaneous one (PtCO2), in particular when rapid changes of CO2 might be induced by exercise. The evaluation will be done in 2 different settings: * intensive care patients, equipped, for their routine clinical care, with an arterial line; this allows for a precise timed comparison between PaCO2 and PtCO2 readouts; * routine exercise test, where blood gas evaluation is done essentially by means of arterialized earlobe capillary sampling. Following assessment of validity of the measurement (and the lag time PaCO2-PtCO2 which might be necessary to introduce as a correction), evolution of dead space during excise test will be tested in different conditions: Healthy subjects, patients with Chronic Obstructive Pulmonary Disease (COPD), chronic heart failure (CHF), hyperventilation, Pulmonary artery hypertension (PAH), or interstitial lung disease (ILD)

Inclusion Criteria: * Written and informed consent, and assent where required. * Either: Patients in intensive care, conscious and in stable hemodynamic condition, who are already equipped with an arterial line for blood gas analysis (as required by the routine practice in intensive care; no arterial line shall be inserted for the purpose of this study) (Part A1) Or patients/subjects scheduled for routine cardio-pulmonary exercise testing. Among these, the following patients will be included: COPD, PAH, healthy subjects, hyperventilation, chronic cardiac failure, interstitial lung diseases (ILD) (Part A2 and Part B) Exclusion Criteria: * Non-French speaking patients/subjects * Unstable hemodynamics * Local cutaneous lesion or infection * Arterial disease such as fistula * Women with the following condition: pregnancy, breast feeding * Persons deprived of liberty (according to article L1121-5 to L1121-8 of the French Public Health Code)