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Medical gas therapy


Medical gas therapy has been used in medicine since the use of oxygen therapy.

Nitric oxideNitric oxide is a gas that is inhaled. It works by relaxing smooth muscle to widen (dilate) blood vessels, especially in the lungs.Nitric oxide is used together with a mechanical ventilator to treat respiratory failure in premature infants.

Heliox — In medicine heliox generally refers to a mixture of 21% O2 (the same as air) and 79% He, although other combinations are available.

Heliox generates less airway resistance than air and thereby requires less mechanical energy to ventilate the lungs. "Work of Breathing" (WOB) is reduced. It does this by two mechanisms:

Heliox has a similar viscosity to air but a significantly lower density (0.5 g/l versus 1.2 5g/l at STP). Flow of gas through the airways comprises laminar flow, transitional flow and turbulent flow. The tendency for each type of flow is described by the Reynolds number. Heliox's low density produces a lower Reynolds number and hence higher probability of laminar flow for any given airway. Laminar flow tends to generate less resistance than turbulent flow.

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. The Hagen–Poiseuille equation describes laminar resistance. In the large airways where flow is turbulent, resistance is proportional to density, so heliox has a significant effect.


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