UBC Theses and Dissertations
Sex differences in the integrated response to high respiratory muscle work during exercise Dominelli, Paolo Biagio
Purpose. The purpose of this thesis was to investigate sex differences in the integrated response to high respiratory muscle work during exercise. To accomplish this, I developed two novel methodologies (Chapters 2 & 4) in order to answer two subsequent research questions (Chapters 3 & 5). Methods. Chapter 2: Using computer software coupled with physiological measurements, I measured the oxygen cost of exercise hyperpnea in healthy subjects. Chapter 3: Healthy men and women performed voluntary hyperpnea while the oxygen cost of breathing was determined. The absolute and relative oxygen cost of breathing was compared between the sexes at different absolute and relative ventilation. Chapter 4: Using readily available components, I developed a proportional assist ventilator that could operate during all exercise intensities. Chapter 5: Healthy men and women completed three time-to-exhaustion (TTE) tests and quadriceps muscle fatigue was measured after each. The first TTE served as a control and during the 2nd and 3rd either a hyperoxic mixture was inspired or the work of breathing was lowered. Conclusion The oxygen cost of breathing can be consistently and reproducibly measured in healthy women when the work of breathing during exercise is precisely matched (Chapter 2). At ventilations above ~55 l min-¹, women have a greater oxygen cost of exercise hyperpnea. During intense exercise, the oxygen uptake of the respiratory muscles in women represents a greater fraction of total oxygen uptake (Chapter 3). A proportional assist ventilator can reduce the work of breathing to <70% of control values while maintaining spontaneous breathing patterns. The degree of unloading can be altered, but not in a precise manner (Chapter 4). Hypoxemia equally influences the development of quadriceps fatigue in both sexes. Conversely, due to their higher oxygen cost of breathing, manipulating the work of breathing has a greater influence on quadriceps fatigue in women. The collection of these studies indicates that the normally occurring work of breathing during exercise influences the integrated response to exercise to a greater degree in healthy women.
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