Little is known about a fairly frequent abnormal pattern of pulmonary function test results: reduced FEV1 and FVC with a normal FEV1/FVC and normal total lung capacity. We term this a nonspecific pattern (NSP). We sought to identify medical conditions having this pattern and to explore mechanisms producing it.
From a database of 80,929 test results, the NSP was found in 7,702 subjects from whom was drawn a random sample of 100 subjects. Medical records and all available tests were examined.
Airway hyperresponsiveness (AHR) and obesity were common. Two groups of subjects were identified. Group A consisted of 68 subjects with evidence of airway disease, including AHR and chronic lung disease. A volume derecruitment model was proposed to explain their NSP. Group B consisted of 32 subjects with no evidence of airway disease. Restricted expansion of the thorax or lung may explain the NSP in most of these subjects. Forty subjects had repeated tests, and in only 17 were the test results consistently nonspecific.
In a random sample of 100 subjects with the NSP, the probable underlying cause of the pattern in 68 subjects was airway disease. In most of the remaining 32 subjects, restricted expansion of the thorax or lung may be implicated.