Interpretation of Spirometry Readings
The spirometry results indicate normal lung function with no evidence of obstructive or restrictive ventilatory defects. The FEV1/FVC ratio of 80% is within normal limits, and there are no concerning findings in the other parameters.
Analysis of Individual Parameters
FEV1/FVC ratio = 80%: This is the most important parameter for identifying obstructive impairment. A normal ratio is typically above the 5th percentile of predicted value 1. The value of 80% is within normal range, ruling out obstructive disease.
FEV1 = 3.77: Without predicted values, we cannot determine the exact percentage of predicted. However, when considered alongside the normal FEV1/FVC ratio, this suggests normal lung function.
FVC = 4.72: Similar to FEV1, without predicted values, we cannot determine the exact percentage of predicted, but in the context of a normal FEV1/FVC ratio, this suggests normal lung volumes.
FEF25-75 = 3.79: This represents mid-expiratory flow and can be helpful in detecting early small airway disease. However, it has greater variability than FEV1 and is less reliable for diagnosis 1.
FET (Forced Expiratory Time) = 5.59: This represents the duration of the forced expiratory maneuver and is typically within normal limits.
Interpretation Framework
When interpreting spirometry, it's important to follow a systematic approach:
Assess FEV1/FVC ratio first:
If FEV1/FVC is normal, check FVC:
- If FVC is below the 5th percentile, this suggests restriction
- Without predicted values, we cannot definitively assess this, but the normal ratio suggests normal function
Consider severity if abnormalities are present:
- Not applicable here as values appear normal
Important Considerations
Using a fixed FEV1/FVC ratio of 70% (as in some GOLD criteria) rather than the statistically defined 5th percentile can lead to misclassification, particularly in younger and older adults 2, 3
Even with a normal FEV1 (≥80% predicted), other spirometric measures may show abnormalities, particularly in conditions like cystic fibrosis 4
When FEV1 and FVC are both decreased but the FEV1/FVC ratio is normal, this could reflect:
- Incomplete inhalation or exhalation
- Very slow flow where the subject cannot exhale long enough
- Patchy collapse of small airways early in exhalation 1
Without predicted values for comparison, we cannot determine if the absolute values of FEV1 and FVC are reduced relative to what would be expected for this individual. However, the normal FEV1/FVC ratio of 80% strongly suggests normal lung function without evidence of obstructive disease.