最大呼气低段流速足指用力肺活量时间曲线(FVC-t)上在肺活量为75～85％之间的流速(FEF75～85％)。该段流速主要由肺弹性回缩力和气道阻力所决定,不受呼气用力强度的影响,能反映小气道的功能。不少呼吸系统疾病在未出现通气障碍的自觉症状之前,常因肺泡的病理变化而累及小气道功能。此时,用常规的肺功能检查法往往未能发现异常,所以探讨敏感指标,争取早期诊断,是呼吸系统临床甚为关注的问题。支气管哮喘患者多表现为 The maximum expiratory flow in the lower expiratory flow means a flow rate (FEF75 to 85%) between 50% and 85% of vital capacity on a FVC-t curve. This section of the flow rate is mainly determined by the lung elastic retraction force and airway resistance, not affected by the intensity of expiratory force, can reflect the function of small airways. Many respiratory diseases in the absence of symptoms of ventilatory disorders before, often due to alveolar pathological changes involving the small airway function. At this point, with conventional pulmonary function tests often failed to find abnormalities, so to explore sensitive indicators for early diagnosis, the respiratory system is very concerned about the clinical issues. Patients with bronchial asthma and more performance