Filling indices for the three gas mixtures in each of four body positions. The FI for the anterior lung was significantly different to the posterior lung for supine and prone position (P < 0.001). Similarly the FI of the left lung was significantly different to the right lung in both the right and left lateral position (P < 0.001). The mean and 95% confidence interval are presented. The dotted line indicates an FI = 1, where the rate of impedance change in the ROI is similar to the global impedance change. # indicates significant differences (P < 0.001) between anterior and posterior, and between left and right respectively.