Degree Name

Doctor of Philosophy


Department of Biomedical Science


The research undertaken in this present investigation had three general aims. First, this project sought to quantify changes in both the elastic and flow-resistive work of breathing that accompany ageing, both at rest and during exercise at three submaximal intensities.

Second, this project uniquely evaluated aged-related changes in the relative and simultaneous contributions ofthe chest wall and lung tissue to total respiratory elastic work. Previous research has not undertaken such a simultaneous assessment, leaving doubtful of their combined influence upon respiratory work in the ageing adult.

Finally, since habitual physical activity has been shown to slow the ageing process within various physiological systems, this project tested the possibility that habitual physical activity could offset age-related effects on mechanical work of breathing, by preventing agerelated stiffening ofthe chest wall, and by helping to maintain the flow-resistive integrity of the airways.

It was hypothesised that:

1.1.1 Ageing will result in a progressive increase in total respiratory elastic work and pulmonary flow-resistive work of breathing.

1.1.2 The changes in total respiratory elastic work will be brought about by an elevation in chest wall elasticity and a reduction in lung tissue elasticity.

1.1.3 The elevation in flow-resistive work encountered during exercise will be greater in older than younger subjects.

1.1.4 Habitual physical activity will act to minimise the effects of ageing on chest wall elastic work of breathing.

These hypotheses were tested using a cross-sectional design, where ageing, in the absence of disease, was investigated in three discrete age groups (20-30 years; 40-50 years; and greater than 60+ years) of males. Pulmonary mechanical changes were fractionated into both elastic and flow-resistive components. Chest wall and lung tissue elastic work were determined from changes in transthoracic and transpulmonary pressures-volume relationships, obtained statically over the entire vital capacity. Flow-resistive work was quantified from dynamic changes in transpulmonary pressure and respiratory flow. Subjects were tested at rest and three exercise loads (two relative and one absolute). Finally, the interaction of habitual physical activity was assessed by using chronically sedentary and habitually physically active subjects.