Which property differentiates helium from nitrogen that makes helium-oxygen mixtures advantageous in airway resistance?

Which property differentiates helium from nitrogen that makes helium-oxygen mixtures advantageous in airway resistance?

• A. Lower density
• B. Higher density
• C. Greater opacity
• D. Higher reactivity

Answer: (A)

The key idea is how gas density affects flow through narrowed airways. Helium is much less dense than nitrogen (and than the nitrogen-oxygen mix that makes up air). In obstructed airways, flow tends to become turbulent and inertial forces from the gas density contribute to higher resistance. By using a helium-oxygen mixture, the overall density of the inhaled gas is reduced, which lowers the Reynolds number for the same flow and decreases turbulent energy losses. This makes the gas move more easily through constricted passages, reducing airway resistance and the work of breathing. The other properties listed aren’t relevant to this effect—heavier gas would worsen resistance, opacity and reactivity don’t drive this outcome.

The key idea is how gas density affects flow through narrowed airways. Helium is much less dense than nitrogen (and than the nitrogen-oxygen mix that makes up air). In obstructed airways, flow tends to become turbulent and inertial forces from the gas density contribute to higher resistance. By using a helium-oxygen mixture, the overall density of the inhaled gas is reduced, which lowers the Reynolds number for the same flow and decreases turbulent energy losses. This makes the gas move more easily through constricted passages, reducing airway resistance and the work of breathing. The other properties listed aren’t relevant to this effect—heavier gas would worsen resistance, opacity and reactivity don’t drive this outcome.