Spirometry is a common breathing test that measures the amount and speed of air you can inhale and exhale. It evaluates lung function and helps understand conditions affecting the respiratory system. Interpreting these results provides insights into your lung health.
Key Measurements Explained
Several key measurements provide distinct information about lung function. Forced Vital Capacity (FVC) is the total volume of air you can forcibly exhale after a full, deep breath. A lower FVC can indicate restricted lung capacity. Forced Expiratory Volume in 1 Second (FEV1) measures the air you can forcibly exhale during the first second of this breath. A reduced FEV1 often suggests airway obstruction.
The FEV1/FVC Ratio is the percentage of FVC you can exhale in the first second. A ratio below 70% is generally considered abnormal and points towards potential airway obstruction. Peak Expiratory Flow (PEF) represents the fastest speed you can exhale air. While FEV1 is considered a more precise indicator of airway obstruction, PEF is often used for daily monitoring, especially for conditions like asthma.
Interpreting the Patterns
Spirometry measurements, especially FEV1 and FVC, help identify distinct lung function patterns. An obstructive pattern is indicated by a low FEV1/FVC ratio, less than 0.70. This suggests resistance or narrowing in the airways, making exhalation difficult. Conditions associated with an obstructive pattern include asthma, chronic obstructive pulmonary disease (COPD), and emphysema.
A restrictive pattern is characterized by a reduced FVC, below 80% of the predicted value, while the FEV1/FVC ratio remains normal, above 0.70. This indicates a reduction in overall lung volume or capacity. Causes include pulmonary fibrosis, obesity, and chest wall deformities like scoliosis. Some individuals may exhibit a mixed pattern, showing features of both obstructive and restrictive issues.
Reading the Graphs
Spirometry results are presented through graphs. The Flow-Volume Loop plots airflow rate on the vertical axis against lung volume on the horizontal axis. A healthy loop shows a rapid rise to a peak flow during exhalation, followed by a steady decline. Deviations from this smooth shape, such as a “scooping out” appearance during exhalation, indicate obstructive lung conditions.
The Volume-Time Curve displays the volume of air exhaled over time. In a healthy individual, this graph shows a rapid increase in volume during the first second, followed by a plateau as exhalation is completed, typically within six seconds. A slower rise to the plateau or a lower overall plateau can suggest impaired lung function.
Personalizing Your Results
Spirometer test results are interpreted by comparing your measured values to “predicted values.” These predicted values are statistical averages derived from large populations of healthy individuals. Factors such as age, sex, height, and ethnicity significantly influence what is considered a typical range for lung function. For example, taller individuals generally have greater lung volumes.
Your results are commonly expressed as a percentage of these predicted values. A score of 80% or higher of the predicted value is generally considered within the normal range for FEV1 and FVC. This personalized comparison accounts for individual characteristics, making the interpretation of your spirometry results more accurate and relevant to your specific lung health.