A REBREATHING METHOD TO DETERMINE CARBON-MONOXIDE DIFFUSING-CAPACITY IN CHILDREN - REFERENCE VALUES FOR 6 18-YEAR-OLDS AND VALIDATION IN ADULT VOLUNTEERS

The diffusing capacity of carbon monoxide (D-L,D-CO) and its value nor malized to alveolar volume (D-L,D-CO/V-A) are usually estimated with t he single breath method at total lung capacity (TLC). Severely ill pat ients and small children are not able to deliver a satisfactory vital capacity (VC) or hold their breath for 10 s at TLC. The aim of this st udy was to develop a rebreathing procedure in which diffusing capacity can be determined during spontaneous tidal breathing. The conventiona l rebreathing method during hyperventilation was modified so that rebr eathing volume and gas concentrations were kept constant by CO2 absorp tion and O-2 supplementation. In adult healthy volunteers and in patie nts who were able to perform both tests, the diffusion indices obtaine d with this rebreathing method during resting ventilation were compare d with those obtained by the single breath method. Predicted (referenc e) values for rebreathing D-L,D-CO and D-L,D-CO/V-A for children were determined. D-L,D-CO/V-A decreased with alveolar volume (V-A) and incr eased with alveolar ventilation (V-A'). In adults at V-A' above 35 L.m in(-1) rebreathing D-L,D-CO/V-A was similar to single breath D-L,D-CO/ V-A at similar alveolar volumes. The D-L,D-CO/V-A relative to their co rresponding reference values were the same for both methods in adult p atients, irrespective of ventilation distribution disturbances. In chi ldren the newly described diffusing capacity obtained by the rebreathi ng method during resting ventilation can serve as a valuable index to assess and follow a diffusion disorder. (C) 1998 Wiley-Liss, Inc.