Jordan Guenette

Introduction: During the coronavirus disease 2019 (COVID-19) pandemic, public health officials have widely adopted the use of face masks (FM) to limit the spread of infection. Despite consistent evidence that FMs increase dyspnea (i.e., breathlessness), no studies have examined the multidimensional components of dyspnea or the physiological mechanisms of dyspnea with FMs. Methods: In a randomized cross-over design, sixteen healthy individuals (n=9 females, 25±3 y) completed three testing sessions separated by ≥48 h. Each visit included a maximal incremental cycling test where visits 2 & 3 were randomized to either FM or control condition. Dyspnea intensity and unpleasantness were assessed using the 0-10 Borg scale and the Multidimensional Dyspnea Profile (MDP) was administered immediately following exercise. Crural diaphragmatic electromyography (EMGdi), esophageal pressure (Peso), and transdiaphragmatic pressure (Pdi) were measured via a specialized catheter to estimate neural respiratory drive and respiratory muscle pressures respectively. Results: Dyspnea unpleasantness was significantly greater with the FM at the highest equivalent submaximal work rate (HESWR) (2.5±2.0 vs. 1.5±1.5 Borg 0-10 units, P=0.01) and at peak exercise (7.8±2.1 vs. 5.9±3.4 Borg 0-10 units, P=0.01) with no differences in dyspnea intensity ratings throughout exercise compared to control. There were also significant increases in the sensory quality of “smothering/air hunger” (P=0.01) and the emotional response of “anxiousness” (P=0.04) in the FM condition. There were significant increases in EMGdi (P=0.001) and esophageal pressure swings (P=0.006) at the HESWR but no differences in heart rate, peripheral oxygen saturation or breathing frequency throughout exercise with FMs compared to control. Conclusions: Our findings suggest that FMs negatively impact the affective domain of dyspnea during exercise and increase neural respiratory drive and respiratory muscle effort requirements during exercise, although the impact on other cardiopulmonary responses are minimal.

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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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The physiological consequences of cycling cadence selection are poorly understood. Purpose: To determine the impact of cadence on cardiorespiratory and metabolic parameters; perceptual responses; power of breathing (Pb); electromyography of the diaphragm (EMGdi) and leg muscles; and microvascular leg blood flow. Methods: Eleven trained cyclists (10M:1F; age=27±6yrs; V̇O2max=60.8±3.7ml·kg-¹·min-¹) completed four 6-min constant-load cycling trials at 10% below their gas exchange threshold (63±5% peak power) while pedaling at 60rpm, 90rpm, 120rpm, and a freely chosen cadence (FCC, 94.3±6.9 rpm), in randomized order, on an electromagnetically braked cycle ergometer. Ventilatory and metabolic parameters were measured using a commercially available metabolic cart. An oesophageal electrode balloon catheter was used to assess Pb and EMGdi. Surface EMG was placed on four leg muscles predominant in cycling. Blood flow index (BFI) was determined on the same muscles of the contralateral limb using near-infrared spectroscopy and indocyanine green. Perceptual responses were measured using the modified 0-10 category ratio Borg scale. Results: With each increase in cadence there was a corresponding increase in V̇O2 (all pairwise comparisons p0.05). Conclusion: Relative blood flow appears to be closely linked with metabolic activity of the muscle, which was significantly elevated during the highest cadence condition. In combination with the substantial rise in respiratory variables and the Pb, cadence may represent the balance between peripheral and central stressors.

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Inspiratory muscle training (IMT) is an efficacious intervention to reduce dyspnoea in health and disease. Growing evidence also suggests that IMT can improve whole body exercise performance. However, the physiological mechanisms for these improvements are not well understood. We sought to examine the effects of IMT on dyspnoea, respiratory muscle electromyography (EMG), and respiratory and locomotor oxygenation to examine potential mechanisms of action for any IMT-related improvements in dyspnoea and exercise performance. 25 recreationally active healthy men completed two maximal incremental cycle exercise tests separated by 5 weeks of randomly assigned pressure threshold IMT or sham control training (SC). The IMT group (n = 12) performed 30 inspiratory efforts twice daily against a 30 repetition maximum intensity. The SC (n = 13) group performed a daily bout of 60 inspiratory efforts against 10% maximal inspiratory pressure (MIP), with no weekly adjustments. EMG electrodes on the sternocleidomastoid (SCM) and scalene muscles measured changes in muscle activity, and near-infrared spectroscopy (NIRS) optodes on the SCM, parasternal intercostals, 7th intercostal space, and vastus lateralis muscle measured changes in oxygenated and deoxygenated haemoglobin during each exercise test. Dyspnoea was measured throughout exercise using the modified Borg scale. Finally, a subset of participants (IMT: n = 11; SC: n = 11) were instrumented with a multi-pair oesophageal electrode catheter containing two balloons, to measure diaphragm EMG and respiratory pressures. IMT significantly improved MIP (pre: -138±45 vs. post: -160±43, cm H₂O, p
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