2. Calculate the total exhaust volume (vital capacity) from the recorded curve, and then calculate the exhaust volume (FEV) of 0.5, 0.75, 1, 2 and 3 seconds, the percentage of exhaust volume per second to vital capacity (FEV%) and the maximum expiratory middle flow rate (MMF). 1, 2 and 3 seconds of exhaust volume and the percentage of exhaust volume per second to vital capacity are commonly used evaluation indexes. Normal people can exhale 80%, 95% in 2 seconds and 99% in 3 seconds within the expiratory time of 1 second. Time vital capacity is a commonly used sensitive index to monitor the impact of air pollution on health.