EFFECT OF PREINSPIRATORY MANEUVER ON THE SINGLE-BREATH D-LCO

We have observed in some patients with pulmonary disease and normal su bjects that the difference between two successive measurements for sin gle-breath D-LCO amounted to 10%. By scrutinizing data from these subj ects, we observed that they spontaneously changed their preinspiratory maneuver just before inhaling the test gas mixture. The purpose of th e present work is to assess the influence of five different preinspira tory maneuvers on D-LCO Nine healthy males were investigated. They per formed at random the five following maneuvers: (A) rapid exhalation fr om functional residual capacity (FRC) to residual volume (RV), (B) rap id exhalation from FRC to RV and long apnea at RV, (C) rapid exhalatio n from FRC to RV and short apnea at RV, (D) slow exhalation at a const ant speed from FRC to RV, and (E) curvilinear exhalation from FRC to R V. The D-LCO values after maneuver B were higher than those after the four other maneuvers; there was a significant relationship between D-L CO and the duration of the preinspiratory maneuver. The data are best explained by an alteration in the distribution of the inspired gas mix ture to areas with different diffusing capacities. In conclusion, the preinspiratory maneuvers must be standardized in order to improve the reproducibility of the single-breath D-LCO measurements.