Heliox improves aerosol deposition and tidal volume in a model of acute airway obstruction

Heliox has been reported to reduce work of breathing and to improve aerosol deposition in patients with acutely obstructed airways. We wanted to evaluate the effects of an aerosol delivery system (Aerogen, Inc, Mountain View, CA, USA) with a prototype heliox delivery system (Datex-Ohmeda, Inc, Madison, WI, USA) incorporating an electronic demand valve with an active exhalation valve, and its impact on aerosol deposition and tidal volume (V_t).

Methods

Air and heliox (70% He, 30% O₂) were administered through a 60 inch coaxial circuit to an absolute filter and active servo test lung (IngMar) set to simulate spontaneous tidal ventilation (rate 20, V_t 500 ml). To simulate airway obstruction, fixed orifice resistors producing resistive pressures of 20 cmH₂O/l per s (Rp20) and 50 cmH₂O/l per s (Rp50) were placed between the distal end of the coaxial circuit and the filter. Three milliliters of 0.083% albuterol (Dey Labs) was aerosolized in an Aeroneb^® Professional Nebulizer placed in the inspiratory limb of the circuit, at the outlet of the prototype heliox delivery device, with both gases and both resistors (n = 3 for each test). Drug was eluted from the filter and assayed to quantify deposition as a percent of the total dose. The delivered tidal volume was measured at the test lung.

Results

Presented in Table 1.

Table 1

Both aerosol deposition and tidal volume were lower with the greater resistance of the Rp50 than with the Rp20. Compared with air, heliox increased tidal volume 30% with both resistors, while deposition increased 30% and 38% (with Rp20 and Rp50, respectively). We conclude that heliox administration improved both tidal volume and aerosol deposition in this in vitro model of airway obstruction.