Decreased expiratory peak flow measurement achieved during forced expiration that primarily reflects changes in upper airway conductance and may be of limited use in evaluation of changes in peripheral airway conductance. Evaluation of peak flow performance is subjective, and, therefore, acceptability criteria are lacking. Because the maneuver is effort and volume dependent, the patient must be encouraged to perform as vigorously as clinically feasible. The results of subjective evaluation may be difficult to interpret consistently. A validated dyspnea rating scale may be useful. [from
NCI]