Physiological Factors Associated with Unsatisfied Inspiration at Peak Exercise in Healthy Adults.

INTRODUCTION: Contrary to common belief, a growing body of evidence suggests that unsatisfied inspiration (UI), an inherently uncomfortable quality of dyspnea, is experienced by ostensibly healthy adults during high-intensity exercise. Based on our understanding of the mechanisms of UI among people with chronic respiratory conditions, this analysis tested the hypothesis that the experience of UI at peak exercise in young, healthy adults reflects the combination of high ventilatory demand and critical inspiratory constraints.

METHODS: In a retrospective analysis design, data included 321 healthy individuals (129 females) aged 25 ± 5 yrs. Data were collected during one visit to the laboratory, which included anthropometrics, spirometry, and an incremental cardiopulmonary cycling test to exhaustion. Metabolic and cardiorespiratory variables were measured at peak exercise, and qualitative descriptors of dyspnea at peak exercise were assessed using a list of 15 descriptor phrases.

RESULTS: 34% of participants (n = 109) reported sensations of UI at peak exercise. Compared to the Non-UI group, the UI group achieved a significantly higher peak work rate (243 ± 77 vs. 235 ± 69 W, P = 0.016, d = 0.10), rate of O2 consumption (3.32 ± 1.02 vs. 3.27 ± 0.96 L·min-1, P = 0.018, d = 0.05), minute ventilation (120 ± 38 vs. 116 ± 35 L·min-1, P = 0.047, d = 0.11), and breathing frequency (50 ± 9 vs. 47 ± 9 breaths·min-1, P = 0.014, d = 0.33), while having a lower exercise-induced change (peak-baseline) in inspiratory capacity (0.07 ± 0.41 vs. 0.20 ± 0.49 L, P = 0.023, d = 0.29). The inspiratory reserve volume to minute ventilation ratio at peak exercise was also lower in the UI vs. Non-UI group. Dyspnea intensity and unpleasantness ratings were significantly higher in the UI vs. Non-UI group at peak exercise (both P < 0.001).

CONCLUSIONS: Healthy individuals reporting UI at peak exercise have relatively greater inspiratory constraints compared to those who do not select UI.