The Effect of Inert Gas Choice on Multiple Breath Washout in Healthy Infants - Differences in Lung Function Outcomes and Breathing Pattern

Detrimental effects on breathing pattern during multiple breath inert gas washout (MBW) have been described with different inhaled gases (100% oxygen, O₂, and sulfur hexafluoride, SF₆) but detailed comparisons are lacking. N₂ and SF₆ based tests were performed during spontaneous quiet sleep in 10 healthy infants aged 0.7-1.3 years using identical hardware. Differences in breathing pattern pre and post 100% O₂ and 4% SF₆ exposure were investigated, and the results obtained compared (FRC and Lung Clearance Index, LCI). During 100% O₂ exposure mean inspiratory flow ("respiratory drive") decreased transiently by mean (SD) 28 (9)% (p<0.001), and end-tidal CO₂ (carbon dioxide) increased by mean (SD) 0.3 (0.4)% units (p<0.05), vs. air breathing pre-phase. During subsequent N₂ washin (i.e. recovery phase) pattern of change reversed. No significant effect on breathing pattern was observed during SF₆ testing. In vitro testing confirmed that technical artifacts did not explain these changes. Mean (SD) FRC and LCI in vivo were significantly higher with N₂ vs. SF₆ 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, SF₆ based MBW is the preferred methodology for tests in this age range.

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