Dependence of forced vital capacity manoeuvre on time course of preceding inspiration in patients with restrictive lung disease.

In normal subjects and patients with airway obstruction, flows during a forced vital capacity (FVC) manoeuvre are higher after a fast inspiration without an end-inspiratory pause (manoeuvre 1) as compared to a slow inspiration with an end-expiratory pause of approximately 5 s (manoeuvre 2). In this study, we investigated the influence of these manoeuvres on maximal expiratory volume-time and flow-volume curves in patients with restrictive lung disease. Eleven patients with restrictive lung disease were studied. Their average (+/-SD) lung function test results were: FVC=55+/-12% predicted value, forced expiratory volume in one second (FEV1) 52+/-20% pred, FEV1/FVC 85+/-6%, total lung capacity 55+/-8% pred, and carbon monoxide transfer factor 47+/-18% pred. The patients performed the two FVC manoeuvres in random order. We compared the ensuing spirograms and maximal expiratory flow-volume curves from which peak expiratory flow, FEV1, FEV1/FVC, maximal mid-expiratory flow, and maximal flows were computed. All spirometric indices were significantly higher with manoeuvre 1 than 2. Maximal expiratory flows at the same lung volume were also significantly higher with manoeuvre 1 than 2, in all patients. Routine spirometric indices, obtained during a forced vital capacity manoeuvre depend on the time course of the preceding inspiration in patients with restrictive lung disease. Therefore, the forced vital capacity manoeuvre should be standardized if used in clinical, epidemiological and research studies.