Second only to hydrogen in universal abundance, helium is an inert, low density gas under atmospheric conditions. 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 medical conditions . Used sporadically for several decades, heliox has been revisited as a 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 mechanics of the respiratory system are determined by both static and dynamic properties. Static properties define the basic pressure-volume characteristics of the respiratory system, and are measured in the absence of airflow. Respiratory system compliance (Crs) is a static property that is determined by the elastic recoil of the lung and chest wall. It can be expressed as:
Crs = change in volume ÷ change in pressure
When applied to tidal breathing, the compliance can be expressed as: