Which components comprise vital capacity?

• A. VT only
• B. VT plus inspiratory reserve volume and expiratory reserve volumes
• C. Residual volume plus tidal volume
• D. Tidal volume plus inspiratory reserve and expiratory reserve volumes

Answer: (B)

Vital capacity is the maximum amount of air you can forcefully exhale after a deep, maximal inhalation. It consists of three parts: the air you normally inhale and exhale in a breath (tidal volume), the extra air you can inhale with a strong effort beyond a normal inspiration (inspiratory reserve volume), and the extra air you can exhale with a strong effort beyond a normal exhalation (expiratory reserve volume). Residual volume—the air left in the lungs after a maximal exhale—is not part of vital capacity because it cannot be expelled. So, adding tidal volume to the two reserve volumes gives you the total vital capacity. In numbers, tidal volume is about 0.5 L, IRV around 1.5–3 L, and ERV about 0.7–1.2 L, totaling roughly 3–5 L depending on body size.