PIP measurement
Figure 1a shows the configuration of this study. A short (25 cm) working-length FB (OD 3.8mm, HYF-V, Olympus), with an inner channel (1.2 mm), inserted via one side (left) nostril. A small pressure transmitting catheter linked the working channel to a real-time pressure monitor (GB30, Galemed, Taiwan). Therefore, the real-time dynamic intra-pharyngeal pressures could be immediately revealed when the FB tip was freely located in the PLS. The PIP was measured at the end of SPI.