The study of diaphragmatic function is usually measured by the pressures and volumes generated by contraction of the diaphragm, which is often difficult (cumbersome technique, difficulty to obtain a perfect cooperation of the subjects, and difficulty to specifically analyze the diaphragm compared to other accessory respiratory muscle groups). In this study, the investigators aimed at analysing diaphragmatic function by measuring the shortening, stiffness, strain and thickening of the diaphragm by ultrasound.