Evaluation by Electrical Impedancemetry of the Variation in Lung Volumes Under Non-invasive Ventilation (NIV) in Patients With Chronic Obstructive Pulmonary Disease (COPD)

The aim of this physiologic research is to assess lung volumes variations under NIV in stable COPD patients to understand the impact of "high-intensity" ventilation following the current recommendations. The main objective is to evaluate the variation of End-expiratory lung volume (EELV) reflecting the functional residual capacity (FRC), via the End-tidal lung impedance (EELI) obtained by electrical impedance tomography during a 20 minutes NIV session.

In patients with COPD, European recommendations recommend the use of NIV with a "high pressure" setting (1). These ventilatory modalities go against what is done in acute. Indeed, in this case, the pressures are much lower, because the risk of asynchronies and dynamic hyperinflation under NIV is then very important. The usual techniques for evaluating lung volume and dynamic hyperinflation do not allow this to be measured under NIV. Assessing lung volumes under NIV in stable COPD patients is therefore of major interest in understanding the impact of "high-intensity" ventilation. Electrical impedance tomography (EIT) is a non-invasive evaluation tool, without radiation, simple to set up at the patient's bedside and validated, making it possible to monitor the distribution of ventilation and lung recruitment with high temporal resolution, dynamic way and at a regional level.(2) Among these measures, the End-Expiratory Lung Impedance (EELI), strongly correlated to the End-Expiratory Lung Volume (EELV), is the reflection of the FRC and can be dynamically monitored in real time at the patient's bedside(3). However, it has never been used in stable COPD patients on NIV, and could be an interesting tool for analyzing the impact of NIV on lung volumes. The main objective is to evaluate the variation of EELV reflecting the functional residual capacity (FRC), via the End-tidal lung impedance (EELI) obtained by electrical impedance tomography, during a 20-minute session of NIV in patients with COPD at the stable state The secondary objectives will be: * To evaluate the variation of the EELV reflecting the FRC, via the EELI obtained by electrical impedance tomography, before, during and after a 20-minute session of NIV in stable-state COPD patients. * Evaluate the relationship between the variation of PtCO2, and that of EELV under NIV, reflection of the FRC, via the EELI obtained by electrical impedance tomography. * Identify responder and non-responder patient subgroups.