Figure 1
Plot of BDVAS and A 1 ratings during limited volume ventilation as a function of change in stimulus intensity (∆P ET CO 2 ). The BDVAS was used to continuously rate breathing discomfort throughout a trial lasting 10 to 15 min; the value shown in this graph is the mean BDVAS over the final 30 seconds of the trial. BDVAS scale ranged from zero to ‘stop now’, which indicated that the subject had reached his or her limit of tolerance. A1 was assessed immediately following the trial, and the subject was asked to focus on the last 30 seconds of the trial when responding. The A1 scale of unpleasantness ranged from ‘neutral’ to ‘unbearable’.