Title: The Mechanics and Energetics of the Aging Pulmonary System during Exercise
Supervisory Committee: Dr. William Sheel (Research Supervisor), Dr. Jordan Guenette; Dr. Donald McKenzie; Dr. Jean-Sébastien Blouin
University Examiners: Dr. William Milsom (Zoology), Dr. Jeremey Road (Medicine)
External Examiner: Dr. Ken O’Halloran
Chair: Dr. Alexander Scott (Physical Therapy)
Abstract: As a part of healthy aging, older individuals experience a decline in respiratory function which makes breathing more difficult, especially during exercise. Purpose: Here, I comprehensively examine the combined effects of healthy aging and biological sex on respiratory mechanics and the metabolic cost of breathing during exercise. Methods: In study #1 (Chapter 2), we validated a newer technology, optoelectronic plethysmography (OEP), which allows us to measure how different groups of respiratory muscles contribute to breathing and proposed a method for quantifying the mechanical work done by the ribcage and abdomen. In study #2 (Chapter 3) we used OEP with healthy adults to understand how differences in regions of the chest-wall contribute to breathing mechanics during exercise with respect to age and sex. In study #3 (Chapter 4) we used voluntary hyperpnea to estimate the metabolic cost of breathing and understand the physiological consequences of different respiratory mechanics across age and sex. Conclusion: Ventilation increases during exercise to meet the metabolic demands of the working muscles and is accompanied by an increased work to breathe. Older individuals and females have a higher work of breathing for a given ventilation and use different regional respiratory muscle to meet those demands relative to younger individuals and males, respectively. With exercise, there is an ample increase in the oxygen uptake by the respiratory muscles. Specifically, both younger and older females have a higher cost to breathe than their male counterparts during moderate and high-intensity exercise and older individuals incur a higher cost to breathe than younger individuals for a given ventilation. Our results suggest that both sex differences and normal age-related changes in respiratory structure and function, appear to have a significant effect on the ventilatory responses during exercise. Collectively, the results of this thesis suggest that sex differences in respiratory mechanics persist throughout healthy aging and contribute to the increased metabolic cost to breathe during exercise in healthy older females relative to males. Understanding the demands of the respiratory system during exercise of healthy older adults is especially important from a clinical perspective given that many diseases of the heart and lungs occur in older individuals.