Abnormality on pulmonary function testing Abnormal RV/TLC ratio 2021-05-01T15:42:55Z Any deviation from the normal ratio of residual volume (RV) to total lung capacity (TLC) on pulmonary function testing. RV is the amount of air remaining aftermaximal expiration and TLC is the total amount of air in theungs at full inspiration. These volumes cannot be determined by spirometry, but can be measured by inert gas dilution, nitrogen washout, and body plethysmography.