Retrospective estimation of values for total lung capacity by plethysmography, helium gas dilution, and chest radiography in patients with cystic fibrosis.

In children with cystic fibrosis, total lung capacity was estimated by helium dilution, plethysmography, and radiography. None of these methods should be used interchangeably as the 95% confidence intervals for estimating were large at 58-144% for radiography and 45.3-100.4% for helium dilution.