Forced expiratory time
The
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 wihtin this time. In the general populations of Vlaardingen
and Vlagtwedde
expiratory times in excess of 10 s were rare (see figure).
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.