Which equation defines tidal volume in terms of flow and inspiratory time?

Which equation defines tidal volume in terms of flow and inspiratory time?

• A. Tidal volume / Ti = Flow required
• B. Te = TCT - Ti
• C. Flow x Ti = Tidal volume
• D. PIP - PEEP = Flow

Answer: (C)

During a controlled inspiration with constant flow, the amount of air delivered (tidal volume) is the flow rate multiplied by the duration of the inspiration. Flow is the volume per unit time, and inspiratory time is the duration, so multiplying them gives the volume delivered: Vt = Flow × Ti. This straight multiplication is why the correct form is the product of flow and to-be-inhaled time. If you rearrange it, Flow = Vt / Ti, which is mathematically the same relationship but the direct expression used in practice is the product, tying flow and time directly to the volume. The other expressions don’t define tidal volume: Te = TCT − Ti concerns timing of the breath (the expiratory time), not the amount of air delivered; PIP − PEEP describes a pressure difference, not the volume moved.

During a controlled inspiration with constant flow, the amount of air delivered (tidal volume) is the flow rate multiplied by the duration of the inspiration. Flow is the volume per unit time, and inspiratory time is the duration, so multiplying them gives the volume delivered: Vt = Flow × Ti. This straight multiplication is why the correct form is the product of flow and to-be-inhaled time.

If you rearrange it, Flow = Vt / Ti, which is mathematically the same relationship but the direct expression used in practice is the product, tying flow and time directly to the volume.

The other expressions don’t define tidal volume: Te = TCT − Ti concerns timing of the breath (the expiratory time), not the amount of air delivered; PIP − PEEP describes a pressure difference, not the volume moved.