The history and physics of heliox.

Since the discovery of helium in 1868, it has found numerous applications in industry and medicine. Its low density makes helium potentially valuable in respiratory care applications, to reduce work of breathing, improve distribution of ventilation, reduce minute volume requirement, and improve aerosol delivery. This review includes a brief history of the use of heliox (a mixture of helium and oxygen) and addresses issues related to the physics of gas flow when heliox is used. Specifically covered are the Hagen-Poiseuille equation, laminar versus turbulent flow, the Reynolds number, orifice flow, Bernoulli's principle, Graham's law, wave speed, and thermal conductivity.

Cost-effectiveness of Advair: fluticasone propionate and salmeterol combination.

The National Heart, Lung and Blood Institute guidelines for the treatment of asthma suggest that inhaled corticosteroids, with the addition of a long-acting bronchodilator, may be the most effective long-term control medication for asthma. Five inhaled corticosteroids are approved for use in the USA, including beclomethasone dipropionate, budesonide, flunisolide, triamcinolone acetonide and fluticasone propionate. Fluticasone propionate (Flixotide) and the long-acting beta2 agonist salmeterol (Serevent), are now available in the USA together in an easy to use dry powder inhaler Advair. The cost-effectiveness of this combination in the treatment of persistent asthma is reviewed. This review evaluates all the cost-effectiveness studies comparing fluticasone propionate and salmeterol from two separate inhalers or one single inhaler available in the literature. Cost-effectiveness was compared with inhaled corticosteroids alone, leukotriene receptor antagonists and other combination therapies in patients with persistent asthma.