Variability and reversibility of the slow and forced vital capacity in chronic airflow obstruction

The variability of the forced (FVC) and slow vital capacity (SVC) manoeuvres were compared in 33 adult patients with chronic airflow obstruction. The reversibility of the two manoeuvres to nebulized salbutamol were compared in 18 of the patients. Both manoeuvres had equally small variances both before and after bronchodilator. The degree of reversibility of the FVC was however significantly greater (P less than 0.05) than the SVC. Although both measurements are equally variable, the FVC has a greater capacity for reversibility, which may have clinical significance.