FEV1 - forced expiratory volume in 1 second, FEV1%VC
The FEV1 is the volume exhaled during the first second of a forced expiratory maneuver started from the level of total lung capacity.
report the largest value of three technically satisfactory maneuvers.
the start of the forced expiration is obtained by linear extrapolation of the steepest part of the volume-time diagram.
the extrapolated volume should not be more than 5% of the FVC or 150 mL, whichever is greater.
the FEV1 reported should not differ by more than 150 mL from the next largest FEV1, or 100 mL if the FVC is 1.0 L or less (procedures, ref. 3) If the difference is larger up to 8 maneuvers (ref. 1) should be performed.
if more than 8 maneuvers would be required to satisfy the criteria, then report the largest FEV1 with a note that reproducible measurements could not be obtained.
FEV1 is by far the most frequently used index for assessing airway obstruction, bronchoconstriction or bronchodilatation; FEV1 expressed as a percentage of the VC is the standard index for assessing and quantifying airflow limitation. In adults, but not in children and adolescent, FEV1%VC declines with age and height.
As IVC > EVC > FVC in patients with obstructive lung disease, the VC should be specified when using the FEV1/VC ratio, hence FEV1%FVC or FEV1%IVC. The Tiffeneau-index is FEV1%IVC (ref. 2).
Ref. 1 - If 8 maneuvers have not led to a FVC or FEV1 meeting the above requirements for reproducibility, then further attempts are useless:
Ferris BG Jr, Speizer FE, Bishop Y, Prang G, Weener J. Spirometry for an epidemiologic study: deriving optimum summary statistics for each subject. Bull Europ Physiopathol Respir 1978; 14: 145-166.
Kanner RE,Schenker MB, Munoz A, Speizer FE. Spirometry in children: methodology for obtaining optimal results for clinical and epidemiological studies. Am Rev Respir Dis 1983; 127: 720-724.
Ref. 2 - Tiffeneau index
Tiffeneau R, Pinelli A. Air circulant et air captif dans lí»exploration de la fonction ventilatoire pulmonaire. Paris Med 1947; 133: 624-631.
Quanjer PhH, Tammeling GJ, Cotes JE, Pedersen OF, Peslin R, Yernault JC. Lung volumes and forced ventilatory flows. Official Statement of the European Respiratory Society. Eur Respir J 1993; 6 suppl. 16: 5-40. Erratum Eur Respir J 1995; 8: 1629.
American Thoracic Society. Standardization of spirometry: 1994 update. Am J Respir Crit Care Med 1995; 152: 1107-1136.
Miller MR et al. Standardisation of spirometry. ATS/ERS task force: standardisation of lung function testing. Eur Respir J 2005; 26: 319-338.