CHANGES IN PULMONARY FUNCTION VALUES
The primary dysfunction of hyperinflation results in an increase in the residual volume (air that cannot be exhaled from the lungs even after a forced effort), which results in the overall increase in FRC. Increased residual volume means there is less effective air exhange.
Forced expiratory manuevers accentuate the collapse of the airways, therefore the patient will have a very prolonged expiratory phase, not uncommon to exceed 6 seconds. While they may be able to eventually exhale a relatively normal VC - the time parameters of 1, 2 or 3 seconds will show greatly reduced volumes at those times in comparison to a normal person without obstruction. Airway collapse also limits exhaled flow rates so those parameters will also be reduced.