T I can be determined when V T and flow are known and the flow pattern is a constant or square waveform.

T I = V T / Flow

If V T is 1.0 L and flow is 2 L/sec, then T I equals 1.0 L/2 L/ sec, or 0.5 sec. The flow control on adult ventilators is usually calibrated in L/min, so the value for flow needs to be converted to L/sec.

Conversely, V T can be determined when T I and flow are known and flow is constant:

V T = flow X T I

If T I is 2 sec and flow is 0.5 L/sec, V T = (2 sec) X (0.5 L/sec) = 1 L