Bronchial Reactivity Tested by a Simplified Eucapnic Hyperventilation System

Abstract

We compared bronchial responsiveness to a simplified method of eucapnic hyperventilation with dry air at an ambient temperature delivered by a simplified system, with eucapnic cold dry air hyperventilation in 20 normal subjects and 20 asthmatic patients. Ventilation calculated to cause a 40% decrease in specific airway conductance for these two methods was almost identical (P>0.05) both in normal subjects (115.45±39.18 and 120.53±59.07 L/min respectively) and asthmatic patients (39.00±12.50 and 38.88±15.14 L/min respectively) ; and they all correlated well with the methacholine inhalation test. All three challenge techniques were almost equally accurate in separating normal and asthmatic subjects. The end-tidal PCO_2 measured by a capnograph confirmed that a single fraction of inspired CO_2 (4.9%) will produce near normal end-tidal CO_2 over a wide range of hyperventilation. The results indicate that this simplified system makes it possible to perform eucapnic hyperventilation challenge without requiring a cooling system or CO_2 monitoring equipment and show that it is potentially a very useful clinical and investigative tool.