A reduction in FVC can be due to either an obstructive or restrictive impairment. Because asbestos exposure is only associated with restrictive impairment, the FEV1/FVC actual measured ratio is necessary to make the distinction. If the FEV1/FVC is below 65% this would indicate that the reduced FVC is a consequence of impaired lung mechanics and, as such, obstructive lung impairment. If the FEV1/FVC is 65% or greater, the reduced FVC would be a consequence of reduced lung volumes and, as such, restrictive lung disease.