FEV1/FEV6 is a ratio that can be used to determine if a person has an obstructive respiratory disease, such as chronic obstructive pulmonary disease (COPD). FEV1 (forced expiratory volume in the first second) is the amount of air a person can exhale in the first second after a deep breath. FEV6 (forced expiratory volume in six seconds) is the amount of air a person can exhale in six seconds after a deep breath.