(a) Preoperative flow volume loop; (b) flow volume loop post-laser treatment. FVC, forced vital capacity; FEV1, forced expiratory volume in 1 s; PEFR, peak expiratory flow rate; FEF₇₅, forced expiratory flow at 75% FVC; FEF₅₀, forced expiratory flow at 50% FVC; FEF_{50 and 75%} maximal expiratory flow measured at the point where 50% of the FVC has expired and after 75% has expired. X-axis, volume in litres; Y-axis, flow in litre s⁻¹.