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

Abstract 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 ( V T ) and ventilation ( V ˙ E ) was observed in each subject. The sense of “work/effort” was the dominant dyspnea descriptor selected up to the V T / 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 V T 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 V T / V ˙ E inflection occurred at a preserved IRV. The V T 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.