People with older age and lower FEV1%pred tend to have a smaller FVC than VC in pre-bronchodilator spirometry

• Characteristics of pre-bronchodilator VCmax > FVC group and VCmax = FVC group were compared.
• Age, gender, FEV1%pred and airway obstruction have independent predicted value for categorization to VCmax = FVC.
• Subjects with older age and lower FEV1%pred tend to have a smaller FVC than VC in pre-bronchdilator spirometry.
• For population with older age and lower FEV1%pred, using FEV1/VC rather than FEV1/FVC as diagnostic indicator will have a greater chance to be classified as obstructive ventilatory defect.

We enrolled 1772 subjects who underwent pulmonary function test before preoperative examination in our study. Pre-bronchodilator forced expiratory volume in one second (FEV1), vital capacity (VC) and forced vital capacity (FVC) were measured as primary data. According to the numerical relationship between VCmax and FVC, two groups were divided: VCmax > FVC and VCmax = FVC. Age, gender, height, weight, BMI and FEV1/FVC, FEV1%pred, FEV1/VCmax were compared between the two groups. Using multivariate logistic regression, factors related to classification of VCmax = FVC or VCmax > FVC were estimated. Of the 1772 spirometric results analyzed, 614 (34.65%) with VCmax = FVC and 1158 (65.35%) with VCmax > FVC were identified. Compared to VCmax = FVC group, subjects in VCmax > FVC group have older age (95%CI [1.50, 3.99], P < 0.001), lower FEV1%pred (95%CI [−12.22, −8.07], P < 0.001) and lower FEV1/VCmax (95%CI [−0.07, −0.05], P < 0.001), parameters such as height, weight, BMI, FEV1/FVC showed no statistical significance. We made a conclusion that people with older age and lower FEV1%pred tend to have a smaller FVC than VC in pre-bronchdilator spirometry.