MERITS OF OXYGEN AIR + HELIUM AS SINGLE-BREATH INDICATORS OF NONUNIFORM DISTRIBUTION OF INSPIRED GAS

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Abstract
Fowler''s single-breath test has been carried out in 23 normal subjects and in 21 patients with pulmonary emphysema, using N2, air, and He as the indicator gas in different experiments. In normal subjects the slope of the alveolar plateau (expressed as addition of unmixed alveolar gas) was, for the single-breath O2 test, 1.0 [plus or minus] 0.87% per 1,000 ml.; and for the He test, 5.3 [plus or minus] 1.9% per 1,000 ml. The N2 slope was believed to be due mainly to inequality of ventilation, but its magnitude might be reduced in normal subjects (but not in patients with obstructive lung disease) by pre-inspiratory, regional inequality of N2 concentration. Because of this, it discriminated better between normality and disease than the He test (which was not affected by VA/Qc Inequality) and appeared to yield a better measure of disability in the present tests. It was consistent with this hypothesis that the single-breath air test (1 breath of air after O2 inhalation) also yielded a significantly larger mean slope than the single-breath N2 test. These single-breath tests have some clinical value as objective methods of assessing defects of gas distribution within the lung, confirming the evidence of simple measures of pulmonary function.