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Physiology and clinical use of heliox

David J Feller-Kopman, MD
Robert Hallowell, MD
Section Editor
Bruce S Bochner, MD
Deputy Editor
Helen Hollingsworth, MD


Helium is an inert, nontoxic gas that is lower in density than nitrogen and oxygen and second only to hydrogen in universal abundance. Discovered in the late 19th century, the first clinical use of helium is indicated by a patent filed by Charles Cook in 1923 for the use of a helium and oxygen mixture (heliox) to decrease the risk of decompression sickness in divers. In 1934, Barach first described the airway physiology of breathing heliox and advocated for its use in a variety of diseases [1]. Heliox has been revisited over the years as a potential therapeutic option for a variety of upper and lower airway conditions.

The physiology and clinical applications of helium-oxygen mixtures in patients with pulmonary disease will be reviewed here. The general management of central airway obstruction is discussed separately. (See "Clinical presentation, diagnostic evaluation, and management of central airway obstruction in adults".)


Therapeutic interventions to improve ventilation often aim to increase static compliance (lung stiffness), decrease airway resistance, or both. To decrease resistance to airflow, bronchodilators and glucocorticoids are often used to increase airway caliber. Another potential method to improve airflow is to alter inhaled gas composition. While the density and viscosity of oxygen, nitrogen, and air are very similar (table 1), substituting helium, a low-density gas, for nitrogen changes the physical properties of the inhaled gas and underlies the theoretical rationale for the clinical application of heliox. Stated differently, by decreasing gas density, airflow resistance can be decreased in the absence of any anatomical change. The following discussion describes the physiology that underlies the effect of gas density on airflow.

Airflow resistance — The mechanics of the respiratory system are determined by both static and dynamic properties. Static properties are measured in the absence of airflow and define the basic pressure-volume characteristics of the respiratory system. Respiratory system compliance (Crs) is a static property that is determined by the elastic recoil of the lung and chest wall.

Dynamic properties of the respiratory system are measured during inhalation or exhalation, when there is a gas flow. Airflow resistance is a dynamic property determined by multiple factors, including:

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Literature review current through: Nov 2017. | This topic last updated: Mar 30, 2017.
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