What is Vital Capacity?
Vital capacity (VC) is the maximum volume of air that can be exhaled after a maximal inspiration. It is one of the most important measurements in pulmonary function testing and reflects the overall ability of the lungs to expand and contract. Vital capacity is composed of three lung volumes:
In healthy adults, vital capacity typically ranges from 3,000 to 5,500 mL (3.0 to 5.5 L), depending on sex, age, height, and ethnicity. It is a critical parameter for assessing respiratory health, surgical fitness, and disease progression.
Lung Volumes and Capacities
| Volume/Capacity | Definition | Typical Value (Adult Male) |
|---|---|---|
| Tidal Volume (TV) | Air moved in/out during normal breathing | 500 mL |
| Inspiratory Reserve Volume (IRV) | Extra air that can be inspired beyond TV | 3,000 mL |
| Expiratory Reserve Volume (ERV) | Extra air that can be expired beyond TV | 1,100 mL |
| Residual Volume (RV) | Air remaining after maximal expiration | 1,200 mL |
| Vital Capacity (VC) | TV + IRV + ERV | 4,600 mL |
| Total Lung Capacity (TLC) | VC + RV | 5,800 mL |
| Functional Residual Capacity (FRC) | ERV + RV | 2,300 mL |
| Inspiratory Capacity (IC) | TV + IRV | 3,500 mL |
Prediction Formulas
This calculator uses the following prediction equations based on height (in cm) and age (in years):
These equations produce predicted values for healthy, non-smoking individuals. Actual measured values are compared to predicted values to determine the percentage of predicted VC, which is the key clinical metric.
Lung Volumes Diagram
Spirometry Basics
Spirometry is the most common pulmonary function test. It measures how much air you can breathe in and out, and how quickly you can expel air. Key measurements include:
- FVC (Forced Vital Capacity): The total volume of air exhaled during a forced expiratory maneuver. In healthy individuals, FVC is essentially equal to VC.
- FEV1 (Forced Expiratory Volume in 1 second): The volume of air exhaled in the first second of a forced expiration. Normally about 75-80% of FVC.
- FEV1/FVC ratio: The key ratio for distinguishing obstructive from restrictive disease. Normal is ≥ 0.70 (70%).
- PEF (Peak Expiratory Flow): The maximum speed of expiration.
Interpretation of Results
| % of Predicted VC | Classification | Clinical Significance |
|---|---|---|
| ≥ 80% | Normal | Lung function within expected range |
| 60% – 79% | Mild Restriction | Slight reduction in lung expansion capacity |
| 40% – 59% | Moderate Restriction | Significant limitation; further evaluation needed |
| < 40% | Severe Restriction | Serious impairment of pulmonary function |
Restrictive vs Obstructive Disease
Reduced vital capacity can indicate different types of pulmonary disease:
| Feature | Restrictive Disease | Obstructive Disease |
|---|---|---|
| VC / FVC | Decreased | Normal or decreased |
| FEV1 | Decreased (proportionally) | Decreased (disproportionately) |
| FEV1/FVC Ratio | Normal or increased (≥ 0.70) | Decreased (< 0.70) |
| TLC | Decreased | Normal or increased |
| Examples | Pulmonary fibrosis, scoliosis, obesity, neuromuscular disease | COPD, asthma, bronchiectasis, cystic fibrosis |
Factors Affecting Vital Capacity
- Height: Taller individuals have larger lungs and higher VC. Height is the strongest predictor of vital capacity.
- Age: VC decreases with age due to loss of lung elasticity and chest wall compliance, starting around age 25-30.
- Sex: Males have approximately 20-25% higher VC than females of the same height and age.
- Physical fitness: Regular aerobic exercise can increase VC by 5-15%.
- Smoking: Chronic smoking reduces VC through inflammation, mucus production, and lung tissue destruction.
- Altitude: Living at high altitude may increase VC as an adaptation to lower oxygen levels.
- Body position: VC is slightly higher when standing compared to sitting or supine positions.
- Ethnicity: Some reference equations include correction factors for ethnicity (e.g., 12% reduction for African American individuals).
- Pregnancy: While tidal volume increases during pregnancy, VC remains relatively unchanged as IRV decreases while ERV decreases.
Worked Example
A 35-year-old male, 175 cm tall:
VC = 175 × (27.63 − 3.92)
VC = 175 × 23.71 = 4,149 mL (4.15 L)
If a spirometry test measured this patient's actual VC at 3,800 mL:
Frequently Asked Questions
What is the difference between VC and FVC?
Vital Capacity (VC) is measured during a slow, relaxed exhalation, while Forced Vital Capacity (FVC) is measured during a forced, maximal-effort exhalation. In healthy individuals, they are essentially the same. In obstructive lung diseases, FVC may be lower than VC because airways collapse during forced expiration (air trapping).
Can vital capacity be improved?
Vital capacity can be modestly improved through regular aerobic exercise, breathing exercises, and smoking cessation. However, the predicted value based on age, sex, and height represents a population norm, and individual variation is normal. Improvements of 5-15% are typical with sustained exercise programs.
Why does vital capacity decrease with age?
As we age, the lungs lose elastic recoil (the tissue becomes less springy), the chest wall stiffens, and respiratory muscles weaken. These changes reduce the total range of motion of the respiratory system, decreasing vital capacity by approximately 20-30 mL per year after age 30.
What does a low vital capacity indicate?
A low vital capacity (below 80% of predicted) may indicate restrictive lung disease (pulmonary fibrosis, chest wall deformity), neuromuscular disease (ALS, muscular dystrophy), obesity, or pleural effusion. However, it can also occur in obstructive diseases when air trapping is present. Further pulmonary function testing (including lung volumes and diffusion capacity) is needed for a definitive diagnosis.
Is vital capacity the same as lung capacity?
No. "Lung capacity" often refers to Total Lung Capacity (TLC), which includes the residual volume (air that cannot be expelled). Vital capacity excludes the residual volume, so TLC = VC + RV. Vital capacity is typically about 80% of total lung capacity.