Analysis of the Relationship Between Dyspnea and Cerebral Cortex Activation Measured by Functional Near-Infrared Spectroscopy During a Spontaneous Breathing Trial

Patient management will not be altered by the study. Patients will be included if the clinician in charge of the patient has decided to perform a SBT on the patient. SBT conditions will be those of current practice. The methods used to measure dyspnea will be those used in current practice in our department (D-VAS and MV-RDOS).

1. Types of measures and techniques used The presence of dyspnea will be defined by a positive response to at least 2 of the following questions: "Does participant feel short of breath?"; "Does participant feel short of air?"; "Is participant's breathing difficult?"; "Does participant have difficulty breathing?". The intensity of dyspnea will be measured by the D-VAS in communicating patients. The dyspnea-VAS will also define patients with clinically significant dyspnea ("D-VAS" > 3) or non-clinically significant dyspnea (D-VAS ≤ 3). Measurement of dyspnea by the MV-RDOS scale will be performed in all patients, and clinically significant dyspnea will be strongly suspected by the MV-RDOS value ≥ 2.6.

Surface EMG of the extra-diaphragmatic inspiratory muscles (Alae Nasi and Parasternal) will be collected via self-adhesive surface electrodes (ECG Electrods, HG91TSG 48x34mm Kendall/Arbo, Covidien, Dublin, Ireland). Bilateral recording of the parasternal muscles will be performed by a pair of electrodes placed in the second intercostal space near the sternum. The recording of the Alae nasi muscles will be performed by placing an electrode on each nostril. Electrical signals of inspiratory muscle activity will be retrieved using the Labchart Peak Analysis MLS380/8 module to extract the root mean square (RMS) of the EMG (RMS-EMG). This envelope of the inspiratory RMS-EMG signal will be used to calculate the maximum EMG amplitude (EMGmax) and its area under the curve (EMGAUC). To minimize artifacts related to ECG activity, the parasternal EMG signal will be filtered before the RMS averaging process, using a low-pass filter (50-400 Hz).

Electroencephalographic activity will be measured with an active electrode system comprising 30 electrodes positioned according to the international EEG 10-20 system, referenced to Fcz (EEG/NIRS device, Artinis Medical Systems®, Einsteinweg, The Netherlands). The impedance of the electrodes will be kept below 5 kΩ. The signals will be amplified and digitized at a frequency of 1000 Hz.

Cerebral perfusion will be assessed using a 27-channel fNIRS tool (EEG/NIRS device, Artinis Medical Systems®, Einsteinweg, The Netherlands). This fNIRS device uses two wavelengths of near-infrared light (695 and 830 nm) to measure relative changes in oxyhemoglobin and deoxyhemoglobin at a sampling rate of 10 Hz. The transmitter and detector optodes are placed 3 cm apart. The cortical areas between each pair of transmitters and detectors are called channels. Anatomically, the channels correspond to the cortical regions located 2-3 cm below the surface of the skin and scalp. The optodes are placed on the forehead and scalp, with the lowest optodes placed along the T4-Fpz-T3 line, defined by the 10/20 system. The fNIRS signals will be processed as described by Schecklmann et al. Oxyhemoglobin, deoxyhemoglobin, and total hemoglobin are derived from the optical densities using the modified Beer-Lambert law. Corrective factors will be applied to remove motion artifacts. An average oxyhemoglobin and deoxyhemoglobin waveform will be generated for each channel. The regions of interest being the premotor cortical areas (supplementary motor area).