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Forced expiratory time in lung function testing

Distribution of forced expiratory timeThe ATS/ERS recommend that an FVC maneuver should take an effort of at least 6 s, and at least 3 s in a child < 10 yrs. However, the FVC maneuver is mostly completed well within this time. In the general populations of Vlaardingen and Vlagtwedde expiratory times in excess of 10 s were rare (see figure). Here is a citation from the Global Lung Function Initiative [1]:
“In a study of adults, carried out in a laboratory [2] that adhered to the quality assurance programme now widely adopted in New Zealand and Australia [3], over 30% of measurements needed to be discarded because they did not meet ATS quality criteria [4]. The great majority of these exclusions related to subjects <30 years; the major stumbling block was the requirement that subjects should exhale for at least 6 seconds. It illustrates that present day quality criteria are not compatible with what is achievable in professionally run laboratories, and need reviewing so as to be uniformly applicable in the field. Strict adherence to the present end of test criteria will lead to biased datasets, for example by favouring young adults with the longest forced expiration times and hence, in all likelihood, a smaller FEV1 and FVC than their counterparts who consistently empty their lungs within 6 seconds. Similar reasoning applies to children.”

A forced expiration resembles a Valsalva maneuver. Particularly when a high intrathoracic pressure is maintained over a longer period, as may occur in patients with obstructive lung disease performing an FVC maneuver, this impedes the venous return of blood into the thoracic cage and leads to blood accumulating in the peripheral vascular bed. This may lead to dizziness, tendency to faint or headache. Therefore it is better not to extend the time of a forced expiration beyond 10-15 s.

The duration of the forced expiration is an important determinant of the FVC; therefore, do not stop the maneuver prematurely.


  1. Quanjer PH, Stanojevic S, Cole TJ, Baur X, Hall GL, Culver B, Enright PL, Hankinson JL, Ip MSM, Zheng JP, Stocks J and the ERS Global Lung Function Initiative. Multi-ethnic reference values for spirometry for the 3-95 year age range: the Global Lung Function 2012 Equations. Eur Respir J 2012; 40: 1324–1343.
  2. Swanney MP, Jensen RL, Crichton DA, Beckert LE, Cardno LA, Crapo RO. FEV6 is an acceptable surrogate for FVC in the spirometric diagnosis of airway obstruction and restriction. Am J Respir Crit Care Med 2000; 162: 917–919.
  3., geraadpleegd 24 maart 2012.
  4. American Thoracic Society. Standardization of spirometry, 1994 update. Am J Respir Crit Care Med 1995; 152: 1107–1136.
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