Helium is an inert gas which is used to reduce the specific gravity of inhaled gas mixtures. It is typically provided as a 0.79/0.21 Helium-Oxygen (Heliox) mixture (though other dilutions exist).

Helium Heliox (0.79/0.21) Oxygen
Specific Gravity (as compared to air) 0.18 0.34 1.09

Reduced specific gravity results in a proportional reduction in Reynolds Number, improving laminar flow within the airways.

Property Action
Class Inert Gas
Uses Obstructive lung disease, deep water diving
Presentation Clear, colourless solution
Route of Administration Inhaled
Dosing Typically as Heliox: 79% He/21% O2
Absorption Diffusion across the alveolar capillary membrane in proportion to membrane area and partial pressure gradient, and inversely proportional to membrane thickness
Distribution Distributes proportionally to solubility and tissue partial pressures
Metabolism Not metabolised
Elimination Respiratory exhalation along a pressure gradient
Resp Significantly decreases the specific gravity of inhaled gas mixtures
Toxic Effects High Pressure Neurologic Syndrome at >16 atm


  1. RAH Advanced Diving Medicine Course Notes: Chapter 6 Oxygen and Carbon Dioxide Toxicity
Last updated 2017-12-22

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