THEORETICAL VALIDATION OF THE RESPIRATORY BENEFITS OF HELIUM-OXYGEN MIXTURES

A theoretical analysis of convective gas transport validates the clini cally demonstrated advantage of using helium-oxygen mixtures in treati ng patients with respiratory problems. Previous studies have attribute d that advantage to the ability of helium-oxygen to stay laminar at hi gher velocities than nitrogen-oxygen. The present work shows that heli um-oxygen does not need to be laminar to provide higher flow rates and that its benefits persist under turbulent conditions. The analysis is applied to steady flow through the lungs and through a circular airwa y obstruction. A simplified model of the lungs gives pressure-flow rel ations that show a significant increase in oxygen flow rate when nitro gen is substituted by helium. A similar improvement is found for flow through an obstruction. For a given pressure difference across the lun gs or across an obstruction, the turbulent flow rate of oxygen increas es by approximately 50% when nitrogen is replaced by helium in a mixtu re containing 20% oxygen.