Tidal volume inflection and its sensory consequences during exercise in patients with stable asthma

Sixteen patients with stable asthma performed a symptom-limited constant work-rate CWR cycle exercise during which breathing pattern, operating lung volumes, dyspnea intensity and its qualitative descriptors were measured.An inflection in the relation between tidal volume (VT) and ventilation (V˙E) was observed in each subject. The sense of “work/effort” was the dominant dyspnea descriptor selected up to the VT/V˙E inflection, whereas after it dyspnea intensity and the selection frequency of “unsatisfied inspiration” rose steeply in 37.5% of subjects in whom inspiratory reserve volume (IRV) had decreased to a critical level of 0.6 L at the VT inflection point. In contrast, dyspnea increased linearly with exercise time and V˙E, and “work/effort” was the dominant descriptor selected throughout exercise in 62.5% of subjects in whom the VT/V˙E inflection occurred at a preserved IRV.The VT inflection during exercise in patients with stable asthma marked a mechanical event with important sensory consequences only when it occurred at a critical reduced IRV.

► The tidal volume inflection during exercise in patients with mild stable asthma marks a mechanical event with important sensory consequences only when it occurs at a critical reduced inspiratory reserve volume. ► Changes in dynamic respiratory mechanics from before to after the tidal volume inflection point do influence the ability to perceive critical mechanical constraints on tidal volume expansion even in mild stable asthma. ► The analysis of qualitative aspects of breathlessness enhances our understanding of the sensory mechanisms of symptom perception in mild stable asthmatics during cycle exercise, and may have important clinical implications in both the management and the therapeutic evaluation of these patients.