Study objectives: The aim of the study was to measure the single-breath diffusing capacity of the lung for carbon monoxide (D(LCO)sb) in healthy subjects in the following two conditions originally proposed by the American Thoracic Society (ATS) guidelines: relaxation against the shutter; and full inspiration without straining.
Setting: D(LCO)sb was measured in 76 young adults in duplicate, in the two conditions. Mouth pressure was recorded during all of the trials.
Results: The mean (+/- SD) value of the duplicate D(LCO)sb measurements was higher when measured with the patient in the nonrelaxed condition than in the relaxed condition (32.65 +/- 7.65 vs 31.54 +/- 7.11 mL/min/mm Hg, respectively; p < 0.001). The mean effective alveolar volume measured during the single-breath maneuver (VAeff) was also higher in the nonrelaxed condition (VAeff: nonrelaxed condition, 5,779 +/- 1,093 mL; relaxed condition, 5,596 +/- 1,097 mL; p < 0.001), at least as a consequence of a higher inspiratory volume (Vin) in the nonrelaxed condition (nonrelaxed condition, 4,378 +/- 900 mL; relaxed condition, 4,232 +/- 902 mL; p < 0.001). Asking the subject performing a D(LCO)sb maneuver to relax on the shutter during apnea lowers the D(LCO)sb value by approximately 3.4% in comparison to full inspiration without straining, at least in part because it results in a reduced Vin.
Conclusion: These data lend further support to the new European Respiratory Society/ATS Task Force recommendations (full inspiration maintained with near atmospheric intrapulmonary pressure).