Lab Lung function test: decrease of airflow rate and tidal volume increase of reserve volume. Blood gas test shows a decrease in Pao2 an initial Paco2 decline may be noted and an elevation follows with progression. ph decreases in the late stage. during the interval of attack, lung function is usually normal except the reserve volume is increased. Daily test of Pef and its variance is helpful for the judgement of the existence of subclinical asthmaLab •Lung function test：decrease of airflow rate and tidal volume, increase of reserve volume. Blood gas test shows a decrease in PaO2; an initial PaCO2 decline may be noted and an elevation follows with progression. pH decreases in the late stage.during the interval of attack, lung function is usually normal except the reserve volume is increased. Daily test of PEF and its variance is helpful for the judgement of the existence of subclinical asthma