Evaluation of Supranormal Spirometry Values With an Obstructive Ratio for Airway Hyperreactivity

Area of Science:

• Pulmonary Medicine
• Respiratory Physiology

Background:

• Published guidelines suggest elevated FEV1 (>100% predicted) with an obstructive ratio might be a physiological variant.
• Further evidence is needed to determine if this finding signifies symptomatic airway obstruction and guides further evaluation.

Purpose of the Study:

• To investigate whether spirometry findings of normal FEV1 (>90% predicted) and obstructive indices represent a physiological variant or symptomatic airway obstruction.
• To assess the utility of additional pulmonary function tests in differentiating these conditions.

Main Methods:

• Prospective enrollment of 49 patients with FEV1 >90% predicted and FEV1/FVC below the lower limit of normal.
• Comprehensive testing including full pulmonary function tests, impulse oscillometry (IOS), post-bronchodilator testing, fractional exhaled nitric oxide (FeNO), and methacholine challenge testing (MCT).

Main Results:

• Symptomatic patients (n=33) showed higher baseline IOS R5 values compared to asymptomatic patients (n=16).
• Methacholine challenge testing (MCT) was positive in 29% of symptomatic patients.
• The dysanapsis ratio was significantly higher in the symptomatic group.

Conclusions:

• Normal FEV1 (>90% predicted) with obstructive indices may not always be a normal physiological variant.
• Symptomatic patients are more likely to exhibit airway hyperresponsiveness (positive MCT) and elevated IOS values.
• Clinicians should consider evaluating for airway hyperresponsiveness in symptomatic patients presenting with these spirometry findings.