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

Abstract

ABSTRACT 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 yr. 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 Thirty-four percent of participants (n = 109) reported sensations of UI at peak exercise. Compared with 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 per minute, 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 versus non-UI group. Dyspnea intensity and unpleasantness ratings were significantly higher in the UI versus non-UI group at peak exercise (both P < 0.001). Conclusions Healthy individuals reporting UI at peak exercise have relatively greater inspiratory constraints compared with those who do not select UI.