Time constant in the respiratory system is the product of which two factors?

• A. True
• B. False
• C. Not always
• D. Not defined

Answer: (A)

The time constant in the respiratory system is the product of airway resistance and respiratory system compliance. This means how fast the lungs fill or empty depends on both how easily air flows through the airways (resistance) and how stretchable the lungs and chest wall are (compliance).

In a simple view, a single time constant gives about 63% of the change toward the new volume, and three time constants get you about 95%. If either resistance increases or compliance increases, the time constant grows, so filling or emptying is slower. If both decrease, the system responds more quickly.

So the statement that the time constant is the product of two factors is true, with those two factors being airway resistance and respiratory system compliance.