The effect of inert gas choice on multiple breath washout in healthy infants: differences in lung function outcomes and breathing pattern.

The detrimental effects on breathing pattern during multiple breath inert gas washout (MBW) have been described with different inhaled gases [100% oxygen (O) and sulfur hexafluoride (SF)] but detailed comparisons are lacking. N- and SF-based tests were performed during spontaneous quiet sleep in 10 healthy infants aged 0.7-1.3 yr using identical hardware. Differences in breathing pattern pre and post 100% O and 4% SF exposure were investigated, and the results obtained were compared [functional residual capacity (FRC) and lung clearance index (LCI)]. During 100% O exposure. mean inspiratory flow ("respiratory drive") decreased transiently by mean (SD) 28 (9)% ( P < 0.001), and end-tidal CO (carbon dioxide) increased by mean (SD) 0.3 (0.4)% units ( P < 0.05) vs. air breathing prephase. During subsequent N washin (i.e., recovery phase), the pattern of change reversed. No significant effect on breathing pattern was observed during SF testing. In vitro testing confirmed that technical artifacts did not explain these changes. Mean (SD) FRC and LCI in vivo were significantly higher with N vs. SF washout: 216 (33) vs. 186 (22) ml ( P < 0.001) and 8.25 (0.85) vs. 7.55 (0.57) turnovers ( P = 0.021). Based on these results, SF based MBW is the preferred methodology for tests in this age range. NEW & NOTEWORTHY Inert gas choice for multiple breath inert gas washout (MBW) in infants has important consequences on both breathing pattern during test performance and the functional residual capacity and lung clearance index values obtained. Data suggest the detrimental effect of breathing pattern of 100% O and movement of O across the alveolar capillary membrane, with direct effects on MBW outcomes. SF MBW during infancy avoids this and can be further optimized by addressing the sources of technical artifact identified in this work.