Impedance pneumography (IPG) is the method which measures changes in transthoracic electrical impedance with electrodes fastened on patient’s thorax. Respiratory-related changes are a signal which may provide a valuable index of respiration and are considered to be measured in the same way as in impedance cardiography (ICG). These changes are mainly a result of the following effects:1. gas volume increase in relation to the fluid volume displacement during inspiration which causes decrease in conductance, 2. as a result of expansion during inspiration there is an increase of the length of the conductance paths.