What is the inspiratory time-to-expiratory time ratio given the following data: frequency of 12 breaths/min; inspiratory time of 0.90 second?

a. 1:0.22 c. 1:4.6
b. 1:2 d. 1:6.4

ANS: C
Inspiratory time-to-expiratory time ratio = Inspiratory time/Expiratory time and Expiratory time = Total cycle time – Inspiratory time. Inspiratory time-to-expiratory time ratio = Inspiratory time/Total cycle time – Inspiratory time. Total cycle time = 60 ÷ 12 = 5 s. Inspiratory time-to-expiratory time ratio = 0.9/5 – 0.9 = 0.9/4.1. Reduce the inspiratory time-to-expiratory time ratio to its simplest form; divide the numerator and the denominator by inspiratory time. 0.9 ÷ 0.9/4.1 ÷ 0.9 = 1:4.56, or 1:4.6.