Vital Capacity Calculator

Vital Capacity equals Inspiratory Reserve Volume plus Tidal Volume plus Expiratory Reserve Volume

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What Is Vital Capacity?

Vital Capacity (VC) is the maximum amount of air a person can expel from the lungs after a maximum inhalation. It represents the total exchangeable air volume and is one of the most important measurements in pulmonary function testing. VC is the sum of the inspiratory reserve volume, tidal volume, and expiratory reserve volume.

Worked Example

A spirometry test on an adult female reveals an inspiratory reserve volume of 2.0 L, tidal volume of 0.5 L, and expiratory reserve volume of 0.8 L. Using the formula VC = IRV + TV + ERV, the vital capacity is 2.0 + 0.5 + 0.8 = 3.3 L. This is consistent with a normal vital capacity for an adult female (typical range 3.1 L), suggesting no significant restrictive impairment.

Normal Values and Clinical Significance

Normal vital capacity is approximately 4.8 L in adult males and 3.1 L in adult females, though values vary with age, height, and sex. Reduced VC is a hallmark of restrictive lung diseases (pulmonary fibrosis, scoliosis, neuromuscular disease) and can also occur in severe obstructive disease. Serial VC measurements help track disease progression and assess respiratory muscle strength, particularly in conditions like amyotrophic lateral sclerosis (ALS) and myasthenia gravis.

Frequently Asked Questions

What is the difference between VC and FVC?

Vital Capacity (VC) is measured during a slow, complete exhalation, while Forced Vital Capacity (FVC) is measured during the fastest possible exhalation. In healthy individuals, VC and FVC are nearly identical. In obstructive diseases, FVC may be lower than VC because rapid exhalation causes airway collapse and air trapping.

How does VC relate to Total Lung Capacity?

Total Lung Capacity (TLC) = VC + Residual Volume (RV). The residual volume is the air that remains in the lungs after a maximal exhalation and cannot be measured by spirometry alone. VC accounts for approximately 80% of TLC in healthy adults.

Why is serial VC monitoring important in neuromuscular disease?

In conditions like ALS and myasthenia gravis, declining vital capacity signals progressive respiratory muscle weakness. A VC below 25 mL/kg or a drop below 1 L often prompts discussion of noninvasive ventilation or intubation. Serial VC measurements are among the most reliable bedside indicators of respiratory decline.

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