PURPOSE: A prior retrospective study determined that a normal forced expiratory volume in one second (FEV1) > 90% predicted with obstructive indices may not represent a normal variant as 11% of patients were found to have underlying airway hyperreactivity. This study sought to prospectively determine if patients with an FEV1 > 90% and obstructive indices have objective evidence of airway hyperreactivity based on multiple measures of lung function.
METHODS: Pulmonary function testing (PFTs) databases were reviewed on a monthly basis and patients with technically adequate spirometry studies were enrolled in the study based on an FEV1 > 90% predicted and a forced expiratory volume in one second to forced vital capacity ratio (FEV1/FVC) below the lower limit of normal based on 95th percentile confidence intervals. All patients underwent a standardized evaluation to include full PFTs, post-bronchodilator testing, impulse oscillometry, methacholine challenge testing, and exhaled nitric oxide analysis to evaluate for the presence of airway hyperreactivity.
RESULTS: To date, six patients (4 females, 2 males) have been enrolled in the protocol and completed testing procedures. PFTs demonstrated a mean FEV1 (% pred) = 92.6%, FVC (% pred) = 103.9%, FEV1/FVC = 70.9%; TLC (% pred) = 105.7%, RV(% pred) = 85.7%, and DLCO (% pred) = 79.2%. None of the patients meet the 12% criteria for positive bronchodilator testing with a mean FEV1 increase of 7.2%. Methacholine challenge testing was positive in only one patient. Impulse oscillometry values at 5 Hz/20 Hz and exhaled nitric oxide analysis values were not consistent with the presence of airway hyperreactivity.
CONCLUSION: The majority of patients with an obstructive indices and elevated FEV1 > 90% do not have airway hyperreactivity based on post-bronchodilator and methacholine challenge testing despite the presence of airway symptoms such as cough and dyspnea.
CLINICAL IMPLICATIONS: A normal FEV1 > 90% predicted with obstructive indices may not consistently represent a normal physiological variant. Based on airway symptoms, clinicians should evaluate for airway hyperreactivity even in the presence of an elevated FEV1.
DISCLOSURE: Tokunbo Matthews, No Financial Disclosure Information; No Product/Research Disclosure Information