Modes of SPI
SPI (NC, inspiration) processed in four modes of different duration (0, 1, 3 and 5 seconds) consecutively, as depicted in Figure 1b. Each SPI maneuver was performed twice at same duration, then processed to the next mode. Each SPI was followed by an open-nose (deflation) period of 10 seconds for expiration and spontaneous breathing. PIP reading was measured and recorded levels for these maneuvers in the PLS.