To the Editor.—

The study by Martinón-Torres et al using heliox therapy in infants with acute bronchiolitis makes me question the diagnosis of “bronchiolitis” in those infants. It appears from the study that the use of heliox helped to decrease the work of breathing in these infants. It is conceivable that this was achieved by its property of having lower density. It is also known that heliox has higher viscosity, which affects the laminar flow. Laminar flow is the predominant flow in the peripheral airways or bronchioles. Therefore, patients with true “bronchiolitis” where the inflammation and obstruction is in the peripheral airways will have decreased flow with heliox and increased work of breathing. Because this didn’t happen in these infants, one could say that they didn’t have “bronchiolitis” but bronchitis, where the inflammation and obstruction is in the more central airways. These infants had wheezing, implying that they...

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