Influence of leak location and breathing cycle on functional residual capacity (FRC) and lung clearance index (LCI): overview of the influence of continuous leaks on FRC and LCI applied at different locations and phases of the breath cycle

InspiratoryFRC ↑#NAFRC ↑#FRC ↑#
ExpiratoryFRC ↓NAFRC ↓FRC –
Inspiratory and expiratoryFRC ↑#FRC ↑#FRC ↑#FRC ↑#
LCI ↑#LCI ↑#LCI ↑#LCI ↑#

Arrows indicate the direction of change of FRC and LCI from baseline values. NA: not applicable. #: in continuous leaks of a certain size, the end of washout criteria were not reached, and FRC and LCI could not be calculated; : side-stream leaks are independent of inspiration and expiration as there is a constant flow into the side-stream and results are similar to inspiratory and expiratory leaks; +: the change in LCI following pre-capillary expiratory leaks is dependent on when the leak was applied during the washout (further details provided in table 2).