Fractional ventilation (i.e. the distribution between left and right lung), as well as the center of ventilation of the left and right lung, also remained constant throughout the study period (Table 3) . Table 4 summarizes the effect of mechanical ventilation with heliox on indices of gas exchange and V D /V T . Elimination of CO 2 defined by the VI (P = 0.661), as well as a reduction in V D /V T (P = 0.929) was not positively influenced by MV with heliox. Importantly, oxygenation as defined by the OI (P = C stat = static compliance; EIT = electrical impedance tomography; N/A = not available; PaCO 2 = partial pressure of arterial carbon dioxide; PaO 2 = partial pressure of arterial oxygen; PEEP = positive end-expiratory pressure; PEFR = peak expiratory flow rate; PIP = positive inspiratory pressure; Pt = patient; R rs = respiratory system resistance.