An increase of at least 12% and 200 ml in FEV after inhaling a short-acting bronchodilator indicates significant reversibility and confirms the presence of asthma. The FEV/FVC ratio is less than 65% predicted. Airway resistance is increased, so FEV is reduced out of proportion to FVC reduction. Portable peak flow meters are used to monitor ongoing lung function. Patients are instructed how to measure peak expiratory flow, an indicator of the degree of airflow obstruction in the large airways by using the peak flow meter on a regular basis.