Measurement of O2 diffusing capacity of the lungs with a stable O2 isotope.

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Abstract
The rate of disappearance of a stable 02 isotope, 02 34, from the alveoli during breath holding was used to measure the single breath O2 diffusing capacity of the lungs (DLO2SB). In 5 resting subjects at an average O2 pressure (Po2) of 42 mm Hg DL02SB was 33 ml/(min. x mm Hg) and the simultaneously measured CO diffusing capacity was 44 ml/(min. x mm Hg). In 3 of the subjects DL02SB was measured at a Po2 of approximately 220 mm Hg and found to be only 6 ml/(min. x mm Hg). This finding is attributed to the slower velocity of the reaction of 02 and hemoglobin at the higher 02 tensions. The alveolar-end capillary 02 gradient (A-a gradient) calculated from the average values of DL02SB found in our subjects by the Bohr integration procedure was 2 to 3 mm Hg at an alveolar Po2 of 47 mm Hg and less than 0.5 mm Hg at an alveolar Po2 of 100 mm Hg. DL02 SB calculated from the CO diffusing capacity was almost twice as great as the value obtained by directly measuring DLO2SB with 0234. This discrepancy could not be explained by uneven distribution of alveolar volume and diffusing capacity throughout the lungs but could be explained by uneven distribution of diffusing capacity and blood flow (uneven DL/Qc).