THE REFRACTORY PERIOD AFTER EUCAPNIC VOLUNTARY HYPERVENTILATION CHALLENGE AND ITS EFFECT ON CHALLENGE TECHNIQUE

To evaluate whether there is a refractory period (RP) after hyperventilation challenge, we compared the bronchoconstrictive response to repetitive eucapnic voluntary hyperventilation challenge with dry, room temperature air (EVH). The serial challenges were identical with 11 known asthmatics hyperventilating for 6 min at a target minute ventilation of 30 times their FEV(1) measured before either challenge. There was a significant difference between the mean postchallenge fall in FEV(1) to the initial EVH challenge (27.4+/-9.8%) and the response to the second EVH challenge (16.1+/-5.9%) (p=0.0001), indicating refractoriness. We then evaluated whether 6 min of uninterrupted EVH challenge gives a similar bronchospastic response to that which results from an equivalent (by total minute ventilation) interrupted challenge of 2 min of EVH repeated three times. The mean postchallenge fall in FEV(1) in response to this interrupted challenge was 18.9+/-10.6%, which was significantly different from the 27.4% fall in response to 6 consecutive minutes of EVH (p=0.036). This study demonstrates that there is a refractory period after repeated EVH challenges and this refractoriness affects the response to interrupted, or dosed, EVH challenge.