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The effect of diaphragm fatigue on the multidimensional components of dyspnea and diaphragm EMG during exercise Boyle, Kyle Geoffrey

Abstract

Purpose: To determine the effect diaphragm fatigue (DF) has on the multidimensional components of dyspnea and diaphragm EMG (EMGdi) during exercise. Methods: Sixteen healthy males (age=27, V̇O2Max=45.8 ± 9.8) underwent three study visits. Visit 1 comprised of an incremental cycle exercise test to determine maximal work rate. The following two visits involved a constant work rate (CWR) exercise test at an intensity equal to their gas exchange threshold (GET) plus 60% of the delta between GET and peak. One of the two CWR exercise tests was performed following pressure threshold loading (PTL) to induce DF, while the other served as a control. PTL involved inspiring to 60% of maximum transdiaphragmatic pressure (Pdi) to overcome a weighted load in order to initiate inspiration. DF was assessed by measuring transdiaphragmatic pressure in response to cervical magnetic stimulation of the phrenic nerves. Pdi and EMGdi were both assessed by the same esophageal balloon catheter. Breathing intensity, unpleasantness and leg discomfort ratings were assessed with the modified 0-10 category ratio Borg scale. Participants were also asked to select applicable breathing sensations during and after exercise. Peak dyspnea responses were assed via the Multidimensional Dyspnea Profile (MDP). Results: Exercise performance decreased by 1.7 minutes in the pre-fatigue condition compared to control (p=0.04). There were no changes in breathing intensity and leg discomfort (p>0.05) throughout exercise. Breathing unpleasantness increased in the pre-fatigue condition by 0.2 (p=0.09), 0.6 (p=0.04), and 0.6 (p=0.04) units at all three of the dyspnea measurement points achieved by every participant during exercise. One additional time point achieved by fifteen of the sixteen participants increased by 0.9 units (p=0.03). There were no differences in EMGdi. EMGdi significantly correlated with intensity and unpleasantness ratings in both conditions (all p

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