The volunteer will remain lying down for a period of 5 minutes in spontaneous breathing and after this period the diaphragmatic and inferior vena cava ultrasound outcomes will be evaluated.

When using CPAP, these same outcomes will be evaluated at three different PEEP levels, namely: 5, 10 and 15 cmH2O after 5 minutes of use.

During the use of Bi-level, we will maintain the PEEP value at 5cmH2O and modify the pressure support (PS) ventilation values, establishing the following values: 5, 7 and 10 cmH2O of PS, with all outcomes also being evaluated at the same time. end of 5 minutes.

Ventilation support that does not require an artificial airway that aims to reverse respiratory muscle fatigue and decrease the work of the respiratory muscles, maintaining a positive pressure, allows alveolar recruitment, preventing atelectasis and airway collapse. NIV can be administered using continuous positive airway pressure (CPAP) or two levels of airway pressure (Bi-level).

Diaphragmatic ultrasound is a useful technique for evaluating diaphragm function. To evaluate atrophy, it will be necessary to evaluate the thickening fraction (EF). A high-frequency linear transducer (7-13 MHz) will be placed over the ZA, between the eighth and ninth intercostal space, usually 0.5-2.0 cm below the costophrenic angle, between the anterior axillary line and the axillary line. medium, at a depth of 1.5 to 3 cm. The thickening fraction will be measured from the center of the pleural line to the center of the peritoneal line, at the end of expiration (Tdi-exp) and then at the end of inspiration (Tdi-insp), in modes B and M. calculated as follows:

FE = Tdi-insp - Tdi-exp × 100 Tdi-exp

Diaphragmatic mobility (MD) is measured by visualizing the hemidiaphragms through the anterior subcostal route with the convex probe below the costal margin between the midclavicular line and the anterior axillary line, the ultrasound shows the diaphragm as a deep curved structure that separates the thorax from the abdomen. To quantify mobility and diaphragmatic thickening objectively, it is necessary to evaluate at least three images and calculate the average of the MD and FE values. During the assessments, we visualize the MD during calm breathing.

The assessment of distension of the inferior vena cava is carried out with a convex transducer, in the subcostal window, below the xiphoid process, so that the evaluator monitors changes in diameter in real time, according to the participant's respiratory movements, thus evaluating the inspiratory and expiratory diameter of the inferior vena cava, which will later be analyzed to obtain the inferior vena cava collapsibility index:

[(Maximum diameter - Minimum diameter) / Maximum diameter] X 100.