Two channels with two electrodes each were placed above and below the right and left sides of the xiphoid process within the seventh and eighth anterior intercostal space. In addition, two channels with two electrodes each were placed on the right and left midaxillary line of the seventh and eighth anterior intercostal space.

Transcutaneous electrical stimulation settings: Frequency (2 hertz); wave length (300 µs);

Two channels with two electrodes each were placed above and below the right and left sides of the xiphoid process within the seventh and eighth anterior intercostal space. In addition, two channels with two electrodes each were placed on the right and left midaxillary line of the seventh and eighth anterior intercostal space.

Transcutaneous electrical stimulation settings: Frequency (35 hertz); wave length (300 µs); Intensity to achieve a visual contraction

A non invasive sham diaphragm electrical stimulation using transcutaneous thoracic probes

Diaphragm ultrasound was conducted using a 4-12-MHz linear array transducer. Diaphragm thickness was measured at end-expiration (Tdi,ee) and end inspiration (Tdi,ei), and thickening fraction (TFdi) was calculated offline as (Tdi,ei-Tdi,ee)/Tdi,ee.

Diaphragm thickeness is measured each day of the study until mechanical ventilation weaning