To Correlate the Difference between Slow Vital Capacity and Forced Vital Capacity with the Severity of Chronic Obstructive Pulmonary Disease

Chronic Obstructive Pulmonary Disease (COPD) is characterized functionally by a decrease in maximal or forced expiratory flow rates. In addition patients with COPD have uneven ventilation, which result in arterial hypoxemia and hypercapnia. Various pulmonary function tests are available to detect lung diseases as well as grading the severity of the diseases using Spirometer, which can include both quiet and forced Vital Capacity maneuver. The Forced Vital Capacity (FVC) is lower than the Slow Vital Capacity (SVC) even in normal individuals and in obstructive patients. In obstructive patients, the difference between the FVC and the SVC increases with the degree of obstruction. Hyperinflation in patients with airway obstruction is determined by the degree of obstruction and by the difference in the vital capacity between forced and slow maneuvers. In clinical settings, FEV1 percent is commonly used to assess the severity of COPD. This study was done to correlate the SVC-FVC difference with severity of the COPD.

This study was carried out in two groups with 30 in each group, Group A as controls and Group B with established COPD patients. Group B were again subdivided into Mild subgroup, Moderate subgroup and Severe subgroup depending on their FEV1% which is commonly used to assess the severity of COPD. Pulmonary function tests parameters (mainly FEV1%, FEV1/FVC%, SVC, FVC) were assessed by Spirometer.

The difference between Slow Vital Capacity and Forced Vital Capacity was increased significantly with increasing severity of COPD. Slow vital capacity and forced vital capacity difference can be used as the predictor of severity of COPD.