What is the normal total lung capacity (TLC)?

• A. 4,000 mL
• B. 5,000 mL
• C. 6,000 mL
• D. 7,000 mL

Answer: (C)

Total lung capacity (TLC) refers to the maximum amount of air the lungs can hold at the end of maximum inhalation. In healthy adults, normal total lung capacity typically ranges from approximately 5,000 to 6,000 mL. The value of 6,000 mL represents a common average for normal TLC, being characteristic of a well-functioning respiratory system.

This capacity takes into account several components, including tidal volume, inspiratory reserve volume, expiratory reserve volume, and residual volume. Each of these volumes contributes to the overall lung capacity, allowing for proper gas exchange and ventilation. The selected answer accurately reflects the general accepted physiological standards for an adult population, supporting the functional needs of the respiratory system in accommodating different breathing demands.

Values such as 4,000 mL or 5,000 mL would be considered on the lower end and may indicate certain pulmonary conditions or reduced lung volume, while 7,000 mL is above normal and could suggest hyperinflation or other pathological conditions. Understanding the normal range is crucial for assessing respiratory health and diagnosing potential lung disorders.