Heliox

[6] Patients with these conditions may develop a range of symptoms including dyspnea (breathlessness), hypoxemia (below-normal oxygen content in the arterial blood) and eventually a weakening of the respiratory muscles due to exhaustion, which can lead to respiratory failure and require intubation and mechanical ventilation.

[7] Heliox has also found utility in the weaning of patients off mechanical ventilation, and in the nebulization of inhalable drugs, particularly for the elderly.

Heliox's low density produces a lower Reynolds number and hence higher probability of laminar flow for any given airway.

In the small airways where flow is laminar, resistance is proportional to gas viscosity and is not related to density and so heliox has little effect.

In the large airways where flow is turbulent, resistance is proportional to density, so heliox has a significant effect.

Because sound travels faster in heliox than in air, voice formants are raised, making divers' speech very high-pitched and hard to understand to people not used to it.

Trimix is a less expensive alternative to heliox for deep diving, which uses only enough helium to limit narcosis and gas density to tolerable levels for the planned depth.