Doctor of Philosophy in Rehabilitation Sciences (PhD)
Respiratory and exercise physiology
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Problem: Dyspnoea is a common and debilitating symptom in patients with fibrotic interstitial lung disease (ILD). Unfortunately, there are no therapies that consistently reduce exertional dyspnoea in this population. Hyperoxia is a potential intervention to acutely address many of the pathophysiological mechanisms thought to be associated with dyspnoea and exercise intolerance in fibrotic ILD. However, additional research is needed to clarify the role and specific physiological and perceptual effects of hyperoxia during exercise in these patients.Methods: Study 1: Twenty fibrotic ILD patients performed two symptom limited constant work-rate cycle exercise tests at 75% of peak work-rate while breathing room air or hyperoxia, in randomized order. Ventilatory responses as well as both the intensity and qualitative dimensions of dyspnoea were measured throughout exercise. Study 2: Fourteen patients with fibrotic ILD completed an incremental cycle exercise test while breathing room air and two constant work-rate cycle exercise tests while breathing room air or hyperoxia. Diaphragmatic electromyography (EMGdi), a surrogate of neural respiratory drive (NRD), was measured with an oesophageal catheter. Neuromechanical uncoupling (NMU) was calculated as the ratio between EMGdi (% max) and tidal volume (% vital capacity). Dyspnoea intensity was recorded throughout exercise. Study 3: Sixteen patients with fibrotic ILD performed incremental and constant work-rate cycle exercise tests while breathing room air until exhaustion, wherein dyspnoea quality was evaluated throughout exercise. Conclusions: Study 1 demonstrated that hyperoxia results in clinically significant improvements in exercise tolerance, dyspnoea intensity, and dyspnoea quality. Study 2 found that dyspnoea intensity was more strongly associated with estimates of NRD than NMU during normoxic incremental cycling. However, improvements in dyspnoea intensity with hyperoxia were more strongly correlated with NMU than NRD. Study 3 showed increased work/effort was the dominant descriptor of dyspnoea throughout incremental and constant work-rate cycle exercise, but there was an increase in the selection of unsatisfied inspiration once further tidal volume expansion was constrained. Collectively, these results may contribute to the development and enhancement of symptom management in patients with ILD. In the context of rehabilitation, this may translate into improvements in patient outcomes from exercise training programs.
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
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.
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