Kern D G, Patel S R
Division of General Internal Medicine, Memorial Hospital of Rhode Island, Pawtucket 02860.
Chest. 1991 Sep;100(3):636-9. doi: 10.1378/chest.100.3.636.
Seeking an inexpensive, readily available, clinical, screening, and field surveillance test of airway obstruction, we determined the validity of current dogma that forced expiratory time (FET) is a good clinical test of airway obstruction yet is of no epidemiologic use given excessive intrasubject variability.
Two hundred twenty-nine white male plumbers and pipefitters were evaluated by spirometry, chest roentgenography, and a standardized respiratory questionnaire during a union-sponsored asbestos screening program. Subjects were classified as having large airway obstruction (LAO), small airway obstruction (SAO) alone, or no obstruction, on the basis of standard spirometric prediction equations. Two physicians, blinded to clinical and spirometric data, independently measured FET while auscultating the trachea with a stethoscope. The FET was defined as the time taken for an individual to forcefully exhale through an open mouth from total lung capacity until airflow became inaudible. Five such times were recorded for each subject. The mean of the three times having the narrowest range was deemed the FET for calculating test sensitivity and specificity. Based on previous literature, an FET greater than or equal to 6 s was considered abnormally prolonged.
Two hundred five subjects completed both spirometry and FET testing; 67 had LAO, 5 SAO, and 133 no obstruction. A total of 83 percent had three FETs reproducible within a range of less than or equal to 1 s. The sensitivity and specificity of FET for LAO were 92 and 43 percent, respectively, while for SAO alone, 60 and 44 percent, respectively. Overall, FET misclassified 56 percent of nonobstructed subjects. Adjusting the normal-abnormal cutoff points for both FET and SAO minimally improved the performance of FET.
Although FET is a simple, inexpensive, sensitive, and fairly reproducible clinical test of LAO, it cannot be recommended as a clinical or an epidemiologic tool because of its extremely low specificity.
为寻找一种廉价、易于获得的用于气道阻塞的临床筛查和现场监测测试，我们确定了当前一种观点的正确性，即用力呼气时间（FET）是气道阻塞的一项良好临床测试，但鉴于受试者个体内差异过大，它在流行病学方面并无用处。
在一项工会赞助的石棉筛查项目中，对229名白人男性水管工和管道安装工进行了肺功能测定、胸部X线检查以及标准化呼吸问卷评估。根据标准肺功能预测方程，将受试者分为患有大气道阻塞（LAO）、仅患有小气道阻塞（SAO）或无阻塞。两名对临床和肺功能数据不知情的医生，在使用听诊器听诊气管的同时独立测量FET。FET定义为个体从肺总量通过张开的嘴用力呼气直至气流听不见所花费的时间。为每位受试者记录5次这样的时间。取范围最窄的3次时间的平均值作为FET，用于计算测试的敏感性和特异性。根据以往文献，FET大于或等于6秒被认为异常延长。
205名受试者完成了肺功能测定和FET测试；67人患有LAO，5人患有SAO，133人无阻塞。总共83%的受试者的3次FET在小于或等于1秒的范围内可重复。FET对LAO的敏感性和特异性分别为92%和43%，而仅对SAO而言，分别为60%和44%。总体而言，FET将56%的无阻塞受试者误分类。对FET和SAO的正常 - 异常分界点进行调整，对FET性能的改善微乎其微。
尽管FET是一种简单、廉价、敏感且相当可重复的LAO临床测试，但由于其特异性极低，不能推荐将其作为临床或流行病学工具。
