Variables and measurements
The main outcome variable of this study was FIO2, prior to beginning the experiment, the oxygen analyzer was calibrated according to the manufacturer’s instructions using 50 psi wall oxygen and air source. Oxygen concentrations were recorded as FO2 insp. and FO2 pre-insp., which are defined as the peak inspiratory and pre-inspiratory phase, respectively (Fig. 3). Oxygen concentrations measurements were obtained at equilibrium, which was assumed to occur when the reading was steady over the 3-min period. FO2 insp. and FO2pre-insp. were recorded for 10breaths and triplicate in each experimental condition.