Pulmonary Function Tests Measured by Spirometry
Spirometry is a common and essential test to evaluate lung function. It measures the volume and flow of air that a person can inhale and exhale. The key parameters assessed include:
- Forced Vital Capacity (FVC)
- Forced Expiratory Volume in 1 Second (FEV₁)
- FEV₁/FVC Ratio
- Peak Expiratory Flow (PEF)
- Forced Expiratory Flow (FEF) at 25–75% of FVC
- Inspiratory Vital Capacity (IVC)
Detailed Description of Pulmonary Function Tests
1. Forced Vital Capacity (FVC)
- Definition: The total volume of air that can be forcibly exhaled after a deep inhalation.
- Significance:
- Normal: Indicates adequate lung capacity.
- Reduced: Suggestive of restrictive lung diseases (e.g., pulmonary fibrosis) or severe obstruction.
2. Forced Expiratory Volume in 1 Second (FEV₁)
- Definition: The volume of air exhaled during the first second of the forced expiration.
- Significance:
- Reflects the degree of airway obstruction.
- Reduced: Indicative of obstructive diseases like asthma or COPD.
3. FEV₁/FVC Ratio
- Definition: The proportion of FVC exhaled in the first second (FEV₁ ÷ FVC).
- Significance:
- Normal: ≥ 85% in children and ≥ 70% in adults.
- Reduced: Indicates obstructive lung disease (e.g., asthma).
- Normal or Increased: Seen in restrictive lung diseases.
4. Peak Expiratory Flow (PEF)
- Definition: The maximum flow rate achieved during forced expiration.
- Significance:
- Indicates the effort and caliber of large airways.
- Useful for monitoring asthma control.
5. Forced Expiratory Flow (FEF 25–75%)
- Definition: The average flow rate during the middle half (25–75%) of FVC.
- Significance:
- Reflects small airway function.
- Reduced: Early indicator of small airway obstruction.
6. Inspiratory Vital Capacity (IVC)
- Definition: The maximum volume of air inhaled after a complete exhalation.
- Significance:
- Assesses inspiratory effort and lung compliance.
Spirometry Diagrammatic Representation
Below is a description of what a typical spirometry graph looks like, with two main components:
- Flow-Volume Loop:
- X-axis: Volume of air (L).
- Y-axis: Airflow rate (L/sec).
- The shape of the loop helps differentiate between obstructive (scooped-out appearance) and restrictive (narrowed loop) lung diseases.
- Volume-Time Curve:
- X-axis: Time (seconds).
- Y-axis: Volume of air exhaled (L).
- A steeper curve indicates normal function, while a plateau or delayed rise indicates obstruction.
Here is a diagram representing the key spirometry graphs:
- Flow-Volume Loop: Shows patterns for healthy, obstructive, and restrictive lung diseases.
- Volume-Time Curve: Demonstrates normal lung function alongside obstructive and restrictive abnormalities.
These graphs are vital for interpreting spirometry results and diagnosing respiratory conditions.
