Which expression defines expiratory time Te in terms of total cycle time TCT and Ti?

Which expression defines expiratory time Te in terms of total cycle time TCT and Ti?

• A. Te = TCT - Ti
• B. Ti = TCT / (I + E)
• C. Te / Ti
• D. 60 / RR

Answer: (A)

Expiratory time is the duration of the expiratory phase of the breath. The total cycle time equals the sum of inspiratory and expiratory times, so TCT = Ti + Te. Solving for Te gives Te = TCT − Ti, which is the direct way to define Te in terms of the total cycle time and inspiratory time. The other expressions don’t match how cycle timing is related: Te/Ti is a ratio, not an absolute time; 60/RR gives the total cycle time, not the expiratory portion; and Ti = TCT / (I + E) misapplies the relationship between cycle time and the I:E proportions.

Expiratory time is the duration of the expiratory phase of the breath. The total cycle time equals the sum of inspiratory and expiratory times, so TCT = Ti + Te. Solving for Te gives Te = TCT − Ti, which is the direct way to define Te in terms of the total cycle time and inspiratory time.

The other expressions don’t match how cycle timing is related: Te/Ti is a ratio, not an absolute time; 60/RR gives the total cycle time, not the expiratory portion; and Ti = TCT / (I + E) misapplies the relationship between cycle time and the I:E proportions.