Question

The normal value of Tidal Volume (TV) in a healthy adult is approximately:

• A. \(500\ \text{mL}\)
• B. \(2500-3000\ \text{mL}\)
• C. \(1100-1200\ \text{mL}\)
• D. \(4500-5000\ \text{mL}\)

Hint:

Tidal Volume is one of four basic lung volumes checked during a spirometry test, along with Inspiratory Reserve Volume, Expiratory Reserve Volume and Residual Volume. Remember that Tidal Volume refers specifically to a single normal, quiet breath, not a forced deep breath, which is why it is much smaller than the reserve volumes.

Answer 1

The Correct Option is A

Concept: Tidal Volume (TV) is the volume of air that is inhaled or exhaled during a normal, relaxed breath. It is one of the important parameters used to measure lung function.

Step 1: Definition of tidal volume. Tidal volume refers to the amount of air moved in or out of the lungs during a single normal breathing cycle.

Step 2: Normal value in humans. In a healthy adult at rest, the average tidal volume is approximately: \[ TV \approx 500\ \text{mL} \]

Step 3: Comparison with other lung volumes. For reference:
• Inspiratory Reserve Volume (IRV) \(\approx 2500-3000\ \text{mL}\)
• Expiratory Reserve Volume (ERV) \(\approx 1100-1200\ \text{mL}\)
• Vital Capacity (VC) \(\approx 4500-5000\ \text{mL}\)

Answer 2

Concept:

• Minute ventilation, the total volume of air breathed in one minute, equals the volume moved in a single breath multiplied by the number of breaths taken per minute: $MV = TV \times RR$.
• Both minute ventilation and the normal resting breathing rate of a healthy adult are separately known physiological constants, so tidal volume can be worked out by rearranging this relationship instead of quoting it directly.

Step 1: Recall the two known physiological constants.
Average minute ventilation of a healthy adult at rest, $MV \approx 6000\ \text{mL/min}$.
Average resting respiratory rate, $RR \approx 12\ \text{breaths per minute}$.

Step 2: Rearrange the minute ventilation relationship to solve for tidal volume.
$TV = \dfrac{MV}{RR}$

Step 3: Substitute the constants and calculate.
$TV = \dfrac{6000}{12} = 500\ \text{mL}$

Final Answer: 500 mL