Given the patient's FEV1/FVC ratio of 13.6%, which of the following is the most appropriate clinical interpretation?
The patient has mild obstructive lung disease, as reflected by the FEV1/FVC ratio. The patient has restrictive lung disease, as indicated by the low FEV1/FVC ratio. The patient has severe airflow obstruction, consistent with advanced COPD. The patient has normal lung function, as the FEV1/FVC ratio is within normal limits.