Performing the apnea of the single-breath carbon monoxide diffusing capacity: relaxation on the shutter or full inspiration with near atmospheric intrapulmonary pressure?
OBJECTIVE
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.


METHODS
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.


CONCLUSIONS
These data lend further support to the new European Respiratory Society/ATS Task Force recommendations (full inspiration maintained with near atmospheric intrapulmonary pressure).
Normand
Hervé
H
Université de Caen-Basse-Normandie, Faculté de Médecine, Laboratoire de Physiologie, Caen, France. normand-h@chu-caen.fr
Lavigne
François
F
Mouadil
Amèle
A
D000328:Adult; D001049:Apnea / Q000378:metabolism*; D002248:Carbon Monoxide / Q000378:metabolism*; D005260:Female; D006801:Humans; D008297:Male; D011659:Pulmonary Gas Exchange / Q000502:physiology*; D012063:Relaxation / Q000502:physiology*; D012119:Respiration
D002248:Carbon Monoxide