The goal of this pilot observational study is to learn about the dynamic impact of the non invasive ventilation on the diaphragm in patient with amyotrophic lateral sclerosis. The main question it aims to answer : can diaphragmatic ultrasound detect differences in diaphragmatic motion (diaphragmactic excursion and diaphragmatic thickening between spontaneous breathing and non-invasive ventilation ?

Participants will receive diaphragmatic ultrasound assessments both under spontaneous breathing and during non-invasive ventilation on their day hospital evaluation for ventilatory support.

Each diaphragmatic ultrasound assessment will be performed on both the right and left hemidiaphragms, with the patient in a semi-recumbent position at 30°, during a maximal inspiratory effort. The following parameters will be measured:

• Diaphragmatic excursion using M-mode ultrasound with a low-frequency convex (abdominal) probe via a subcostal approach
• Diaphragmatic thickening using B-mode ultrasound with a high-frequency linear (vascular) probe via the lateral axillary line

Measurements will be obtained during spontaneous breathing and after 10 to 20 minutes of non-invasive ventilation (NIV), using ventilator settings deemed optimally adjusted by the supervising physician.

Inclusion Criteria:

• Adult patient (≥18 years old)
• Diagnosis of bulbar or spinal amyotrophic lateral sclerosis (ALS) established by a neurologist
• Indication for non-invasive ventilation (NIV) confirmed by the referring pulmonologist for daytime and/or nocturnal alveolar hypoventilation

Exclusion Criteria:

• Continuous (24-hour) non-invasive ventilation
• Patient refusal to participate
• Individual under legal guardianship or judicial protection

Diagnosis of bulbar or spinal amyotrophic lateral sclerosis (ALS) established by a neurologist