Suprathreshold resistive load perception in normal and asthmatic subjects.

The perception of external suprathreshold loads (2.5-44 cm H2O.1-1.s) was determined in 5 normal and 16 asthmatic subjects in order to (1) study the role of the wording given to the subject for rating the inspiratory loads, either 'intensity' or breathing 'discomfort', and (2) compare the sensation to low (2.5-8 cm H2O.1-1.s) and to high (17-44 cm H2O.1-1.s) loads. Normal subjects exhibited accurate rating of the loads regardless of the wording; high loads were estimated as more severe than the low ones, in spite of a long time interval between the two experiments. They were able to discriminate between each pair of loads. On the contrary, asthmatics with chronic airway obstruction demonstrated a poor perception in all experimental conditions. The physiological variables of breathing pattern and mouth pressure were modified in the same manner in the two populations and could not account for the differences in perception. In conclusion, the differences in sensitivity observed between normal and asthmatic subjects were verified for suprathreshold load perception whatever the wording and the level of the loads. Therefore, for this kind of experimental study, it is not useful to study the full scale of the loads. Furthermore, the present methodological approach provides an additional support to the assumption that the asthmatics' poor sensitivity is related to psychological factors such as past experience of loaded breathing.