An I:E ratio of 1:2 means the inspiratory time is related to the expiratory time how?

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Interpreting an I:E ratio is about comparing how long each phase of the breath lasts. A ratio of 1:2 means the inspiratory phase is one part and the expiratory phase is two parts. So the inspiratory time is shorter, exactly half of the expiratory time. For example, if inhalation lasts 0.5 seconds, exhalation lasts 1.0 second, giving a complete breath cycle of 1.5 seconds. The idea is that the ratio expresses duration, not volume: an I:E of 1:2 indicates the breath spends more time on expiration than on inspiration. If the ratio were 1:1, both phases would be equal, and if it were 2:1, inspiration would be longer than expiration.