Data will be analysed and graphs will be created with SPSS version 22 (IBM SPSS Statistics, New York, US) and MedCalc version 13.1 (MedCalc Software, Mariakerke, Belgium). Bland-Altman plots will be used to visualize agreement between the two measurement techniques. For each pair of measurements, the pairwise mean of the breathing parameters will be plotted on the x-axis, and the pairwise difference expressed as a percentage of their mean value on the y-axis. The mean difference and the 95% limits of agreement and their confidence intervals will be represented by horizontal lines in the graphs.