Supramaximal Flows: Comparison between Asthmatics and Patients with Chronic Obstructive Pulmonary Disease

Abstract

Background: The major motive that prompted this study was to investigate whether or not the differences in supramaximal flow (SF) behavior between patients suffering from asthma and patients suffering from chronic obstructive pulmonary disease (COPD) might aid in clarifying the differences in the physiopathology of the two diseases. Objectives: The aim of the present study was therefore to compare SFs in asthma and COPD patients with similar degrees of air-flow limitation. Methods: Twelve asthmatic patients were individually matched with 12 COPD patients by forced expiratory volume during the first second (FEV₁) as a percent (±5%) of the reference value (ΔFEV₁) and by age (±4 years). The subjects performed baseline maximal expiratory flow-volume curves (MEFV) and then repeated the same maneuvers through a valve that occluded the air flow 6 times per second with an open/closed time ratio of 4/1. We then plotted an envelope of the expiration-interrupted curve passing through the SF peaks, measured the increase in flow at 50% of the forced vital capacity between the baseline curve and the envelope curves (ΔVmax₅₀), and compared the FEV₁ of the interrupted curve to the FEV₁ obtained from control MEFV curves (ΔFEV₁). Results: We found significantly higher values for ΔVmax₅₀ (p < 0.03) and ΔFEV₁ (p < 0.01) in the asthmatics compared to the COPD patients. Conclusions: The differences reported here are best explained by a greater preservation of elastic recoil pressure at a similar degree of air-flow limitation in the asthmatics than in the COPD patients.