Correlation of Vital Capacity with Other Indices of Disease in Obstructive Emphysema

Abstract

The pulmonary function studies of 170 patients with evidence of chronic obstructive pulmonary emphysema have been analyzed to determine the status of the vital capacity in this disease and its degree of correlation with other lung volumes and capacities, the RV/TLC ratio and the maximum breathing capacity. Ten per cent of the group with evidence of “moderate” or “advanced” disease demonstrated a VC from 90-130 per cent of normal predicted and would, on the basis of VC measurement alone, be falsely judged as “normal.” Conversely, 35 patients or 21 per cent of the group classified in the “mild” or “moderate” disease categories had abnormally low VC's. Thus, utilizing VC as the sole indicator of disease severity, nearly one-third of the group would be incorrectly evaluated and would represent either “false positive” or “false negative” diagnoses. Although the general trend is for VC to deteriorate with advanced degrees of COPE, exceptions to this occur with sufficient frequency to invalidate use of the VC alone for diagnosis of this condition or estimation of its severity. From the standpoint of function testing, evaluation of a patient should rather be based on complete lung volume determinations, MBC, RV/TLC ratio and pulmonary nitrogen washout curves.20, 21