<prompt> In a patient with fixed respiratory obstruction Helium is used along with Oxygen instead of plain oxygen becauseIt decreases oxygenationIt decreases turbulenceIt decreases the dead spaceIt provides analgesia  <response>: Helium is given as Heliox HeO2,, a mixture of 20 to 80 He and 80 to 20 O2 . It has about 13rd the density of O2 or air.Because helium is highly diffusible, the use of the mixture greatly reduces the work of breathing in a patient with narrowed airways and thus leads to improved aerosol delivery and increased oxygenation in severe asthma. It may also reduce the risk of barotrauma.It decreases turbulence. In COPD, Helium is used along with O2 to decrease the viscosity of gaseous mixture which increases its linearity decreases resistance in pathway.It has lower Reynauds number, is 3 times faster, has low specific gravity low solubility. 