The present invention relates to a method and an apparatus for measuring
Functional Residual Capacity (CO). Further, it relates to a method and an
apparatus for measuring cardiac output (CO). The method comprises the
steps of determining the amount of oxygen and carbon dioxide being
inhaled and exhaled during at least two breathing cycles, identifying at
least one difference between said breathing cycles, and estimating the
FRC and/or CO based on the determined uptake of oxygen and excretion of
carbon dioxide and said identified difference.