Polar plots assessing trending ability of EELV
to track changes in EELV. Panel A refers to the whole set of measurements, and panel B is restricted to data related to changes in EELV greater than 100 mL since a small change in EELV does not reflect trending ability but mainly random error measurement. The radial axis joining 0 to 180° is a 45° clockwise rotation of the line of identity in the four-quadrant plots, and represents agreement. The better the agreement between ΔEELV measurements, the closer data pairs will lie along the horizontal radial axis. The distance from the center of each plot represents the mean change in EELV between methods (mean ΔEELV) at each consecutive time point. Data points located between 315° and 45° refer to time points in which both EELVCT and EELVWI-WO increased (upper right quadrant of the four quadrant plot), while data points located between 135° and 225° refer to consecutive time points in which both EELVCT and EELVWI-WO decreased (lower left quadrant of the four quadrant plot). Data points located between 45 and 135° or 225 and 315° correspond to disagreement in the directional change of EELV between the washin-washout technique and computed tomography. Continuous line represents the angular bias, while dashed lines represent radial limits of agreement. EELVWI-WO, end-expiratory lung volume assessed with the nitrogen washin-washout technique; EELVCT, end-expiratory lung volume assessed by computed tomography; ΔEELV, change in EELV between consecutive measurements.