Title: Trainability of the pulmonary system: Effect of age and sex
Thesis Supervisor: Dr. Bill Sheel
Committee Members: Dr. Lee Romer, Dr. Jordan Guenette
Chair: Dr. Cameron Mitchell
Abstract:
BACKGROUND: Human lungs and airways show little to no adaptation to exercise training such that static lung volumes, flow rates, lung diffusing capacity, and structural elements within the lung-blood gas interface do not change appreciably. However, the muscles of breathing appear to respond positively to training stimuli. In addition, there is some evidence that chronic exercise training modifies the carotid bodies’ contribution to ventilation.
There are observed sex differences within the pulmonary system. Females have smaller airways even when matched for lung size, leading to a higher resistive work of breathing during exercise. Furthermore, females recruit their respiratory muscles more than males for a given ventilation and demonstrate less diaphragm fatigue after exercise. In response to high levels of inspiratory work, young females exhibit less of an increase in blood pressure relative to young males. The mechanisms are not fully understood but may relate to estrogen’s ability to diminish sympathetic activity. There are also potential sex differences in the ventilatory response to hypoxia due to a direct hormonal involvement in regulating breathing.
Aging is associated with changes to the respiratory system, including a greater ventilatory response to exercise relative to young individuals. The greater ventilatory response is accompanied by a greater respiratory muscle activation and a higher work of breathing, which is accomplished with weaker respiratory muscles. The blood pressure response to high levels of inspiratory work is greater in older adults; however, the sex difference observed in young individuals is absent, possibly due to a loss of estrogen in post-menopausal females. The ventilatory response to hypoxia is attenuated in older adults, potentially because of the age-related reductions within the pulmonary system and hypoxic-sensitive cells.
The present thesis is divided into two experimental studies to address an overarching purpose of understanding the effect of sex and age on the trainability of the pulmonary system. STUDY 1: To understand the effects of sex and age on the trainability of the blood pressure response and diaphragm activation during inspiratory resistive work. To accomplish this, young and older females and males will perform five weeks of inspiratory resistive muscle training and five weeks of detraining. Prior to and following training and detraining, a fatiguing inspiratory resistive breathing task while measuring blood pressure and diaphragm activation will be completed. STUDY 2: To reveal the independent and combined effect of sex, age, and training status on ventilatory control. To accomplish this, quantification of ventilation during a resting hypoxic exposure and measurement of the carotid bodies’ tonic input during exercise will be completed.
The proposed work will reveal how the human respiratory system can respond and adapt to physiological stressors and identify independent and combined effects of sex and age. A better understanding of this will be fundamental for optimizing exercise prescription and rehabilitation programs.