Rapid computer-aided radiographic calculation of total lung capacity (TLC).

Methods currently used for determining total lung capacity are either simple but inaccurate in the presence of airways disease (gas dilution) or accurate but not generally available (body plethysmography). The manual radiographic method is accurate both in normals and in patients with airways disease but is very tedious to use. The authors have developed a semi-automatic radiographic method utilizing a position transducer and a small computer which reduces the time for each determination from approximately 20 min. to 1 min. Agreement with manual calculations in 80 controls and 80 patients with airways disease is excellent (average correlation coefficient, 0.9872; average residual error, 2.65% or 156 ml).