Effects of voluntary changes in breathing frequency on respiratory comfort

Previous experiments on voluntary breathing have suggested that spontaneous breathing is partly determined by the minimization of respiratory sensations. However, during instructed breathing, respiratory sensations may be confounded with difficulty in achieving the prescribed pattern. In the present experiment, we tested the hypothesis that the subjective assessment of respiratory comfort and the difficulty in following breathing instructions are closely related. A total of 15 subjects adjusted breathing frequency to prescribed values ranging from 40 to 250% of individual spontaneous levels. Then, they scored the difficulty of this task and the discomfort associated with the target frequency. Difficulty scores sharply increased above 100% (spontaneous level) and discomfort scores displayed a similar shape. A significant positive correlation between discomfort and difficulty was found, thus suggesting a possible influence of the difficulty to follow ventilatory instructions on respiratory sensation scores.