Flow-volume loop (flow-volume plot) and spirometry (volume-time plot) in a patient with moderate airflow limitation (reduced FEV1/FVC ratio and reduced FEV1) on spirometry, but normal PEF. This discrepancy reflects rapid emptying of gas from the trachea and central bronchi, but slowed expiratory flow from the remainder of the bronchial tree.
95%: the low end of the 95% confidence intervals around the mean; FVC: forced vital capacity; FEV1: forced expiratory volume in one second; FET: forced expiratory time; PEF: peak expiratory flow.