EVALUATION OF SINGLE-BREATH HELIUM DILUTION TOTAL LUNG CAPACITY IN OBSTRUCTIVE LUNG-DISEASE

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Abstract
The effect of obstructive lung disease was examined on the single-breath He dilution method of measuring total lung capacity (TLC). In test results of 79 patients, this dilution method underestimated the TLC determined by a radiographic method by a mean of 2.3% in normal subject, 10.4% in patients with mild, 21.8% in those with moderate and 38.0% in those with severe obstruction. The ratio of forced expiratory volume in 1 s to forced vital capacity was used to group the patients; the differences in the degree of underestimation of TLC between groups were significant (P < 0.05). A strong correlation was found between degree of underestimation of TLC by the He method and the severity of obstruction when patients were considered as a continuous population. Using a regression equation based on this correlation, a method for correcting the He dilution TCL was derived. This allows use of this test in patients whose obstructive disease would otherwise render it inaccurate.

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