The normalized delivered helium concentration, [He]
, is plotted against a composite parameter that includes the ratio between the supply gas flow rate and minute ventilation, Q
, and the ratio between inspiratory and expiratory times, t
, for a) the Hi-Ox mask, b) the Heliox21 mask, and c) the standard mask. Error bars represent standard deviations around mean values (n = 3). For each mask, the exponents in the composite parameter were determined through a least-squares fit of Equation (1) to the experimental data. Best-fit curves, and associated R2 values, are shown for each mask.