Effects of Transcutaneous Electrical Phrenic Nerve Stimulation and Transcutaneous Electrical Diaphragmatic Stimulation

The assessment of diaphragmatic mobility will use a "convex" type transducer (2-6 MHz), positioned in the right subcostal space, at the midclavicular line, tilted in the cephalic direction. The B-mode visualization window will initially be used to locate the diaphragmatic hemi-dome. Upon acquiring a good quality image, respiratory excursions will be measured in M-mode, using the inferior vena cava and the gallbladder as anatomical parameters. Diaphragmatic mobility measurement will be considered as the distance, in centimeters, between the baseline at expiration and its greatest vertical displacement at inspiration produced by diaphragmatic movement.

Diaphragm thickness (Tdi) will be obtained using a high-frequency "linear" type transducer (7-13 MHz), positioned over the zone of apposition (ZA) of the diaphragm muscle. The approximate location is between the 8th and 9th intercostal space, between the anterior axillary line and the midaxillary line, 0.5 to 2.0 cm below the costophrenic angle. The depth will be 1.5 to 3.0 cm, and the diaphragm muscle will be identified as the innermost portion of the hypoechoic muscular layer bounded by two hyperechoic membranes, the pleura - superficial line, and the peritoneum - deeper line. "Tdi" will be measured from the inner edge of the pleural line to the inner edge of the peritoneal line at the end of expiration (Tdi-exp); and at the end of inspiration (Tdi-insp).

The thickening fraction will be obtained using a high-frequency "linear" type transducer (7-13 MHz), positioned over the zone of apposition (ZA) of the diaphragm muscle. The approximate location is between the 8th and 9th intercostal space, between the anterior axillary line and the midaxillary line, 0.5 to 2.0 cm below the costophrenic angle. The depth will be 1.5 to 3.0 cm, and the diaphragm muscle will be identified as the innermost portion of the hypoechoic muscular layer bounded by two hyperechoic membranes, the pleura - superficial line, and the peritoneum - deeper line. The localization of structures and measurements will be performed in B-mode. The diaphragm thickening fraction will be calculated as the percentage of thickness increment during inspiration relative to the thickness at the end of expiration.

The assessment of reported sensory discomfort will be measured through the application of the horizontal numerical scale of sensory discomfort. The numerical scale will be presented to participants in its printed version, on standardized paper measuring 10 centimeters in length. The value "0" (zero) will be assigned to the concept of "absence of discomfort," and the value "10" (ten) will be assigned to the concept of "greatest imaginable discomfort."

Safety criteria will be measured through the occurrence of the number of adverse events, including: Mean arterial pressure < 65 mmHg; heart rate > 140 bpm or < 50 bpm; arrhythmias occurrence; oxygen saturation dropping below 88%; temperature increase (above 37.7°C); presence of reported pain above 7 on the visual analog pain scale; presence of burns at the site where electrodes were placed for electrostimulation. The numbers of adverse events will be recorded, along with their classification according to the World Health Organization Patient Safety Document as follows: no harm, minor, moderate, severe, and death.