Which of the following is false about the application of flow triggering on a mechanical ventila-tor?

a. The ventilator measures both input and output flow.
b. Between patient breaths, input flow ex-ceeds output flow.
c. A relative drop in output flow triggers the machine to turn on.
d. Gas flows continuously through the venti-lator circuit.

ANS: B
The ventilator measures the flow coming out of the main flow control valve and also the flow through the exhalation valve. Between breaths, these two flows are equal (assuming there are no leaks in the patient circuit). When the patient makes an inspiratory effort, the flow through the exhalation valve falls below the flow from the output valve. The difference between these two flows is the flow trigger variable.