《2007SATS青少年和成人慢性哮喘治疗指南》内容预览

Spirometric lung function tests, including measurement ofpeak expiratory flow, are useful in the diagnosis, assess-ment of severity and management (monitoring) of asthma.It may be abnormal even when symptoms and signs areabsent. It may also be normal when asthma is quiescent.The commonest abnormality is a reduction in forced ex-piratory volume in 1 sec (FEV1) and peak expiratory flow(PEF). The ratio of FEV1to forced vital capacity (FVC) tobelow 70% is characteristic of obstructive airways disease.The degree of reduction is generally related to severity ofthe asthma. Asthma improvement is usually mirrored by animprovement in FEV1and PEF.
Significant reversibility of the airway obstruction is themajor physiological characteristic of asthma. The stan-dardised criteria are an increase in FEV1of >12% and200 ml, 15-30 min following the inhalation of 200-400 μg ofsalbutamol, or a 20% improvement in PEF from baseline.It should be noted, however, that many asthma patientswill not exhibit reversibility at each assessment, particularlythose on treatment, and thus the test lacks sensitivity andrepeated testing at different visits is advised.
Conversely, asthma can also be confirmed by demonstrat-ing increased hyperresponsiveness to bronchoconstrictorstimuli, particularly in subjects with normal spirometry. Thisis the principle of the methacholine/histamine challengetest. Exercise-induced bronchoconstriction may also beused to diagnose inducible airway obstruction. The FEV1or PEF is measured at baseline and the patient asked toexercise (e.g. run for about 6 min) and the measurementsrepeated 5-10 minutes following cessation of exercise. Afall of 20% in PEF (15% in FEV1) in this setting is supportiveof a diagnosis of asthma. Exercise induced bronchocon-striction may be the only manifestation of asthma in some.

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