Abnormality on pulmonary function testing Reduced forced vital capacity 2019-02-21T12:48:52Z Decreased forced vital capacity An abnormal reduction in the amount of air a person can expel following maximal inspiration. Reduced FVC The threshold for an abnormally low FVC is defined as less than the LLN for adults or less than 80 percent of predicted for those five to 18 years of age, indicating a restrictive pattern. The LLLN (lower limit of normal) is a measurement less than the fifth percentile of spirometry data obtained from the Third National Health and Nutrition Examination Survey (NHANES III).