Although oxygen transport (i.e. maximal cardiac output) is the usual determinant of maximal exercise capacity (i.e. VO2UAX ) in healthy humans, it is not the sole determinant of exercise performance. Whilst the potential capacity of the respiratory system has been described as being 'over-built' for exercise, a number of respiratory system functions have been linked with exercise limitation, in both trained and untrained individuals. The purpose of this research was to examine the effect exercise has on the functions of the respiratory system. For reasons which will be outlined function of the respiratory system can be described, in part, by airflow profile and breathing pattern. Initially, the tidal airflow profile and breathing pattern, at rest and during exercise of various intensities was examined; specifically looking at how tidal breathing variables are altered in response to increased metabolic demands. Initial findings were that there is vast diversity in the resting tidal breathing profile (« = 148), with significant differences (p<0.05) being observed in a number of variables between males and females. Onset of exercise alters the majority of tidal airflow characteristics but the pattern of change is similar in both sexes. Over a range of exercise intensities the termination of exercise and increased ventilation rates vary, as does the magnitude of some of the respiratory profile changes, but many of the timing changes are the same, particularly those of breathing frequency (fe), the ratio between inspiration and expiration (ti/tToi) and the late occurrence of peak inspiratory flow (tpir). This consistency of characteristic changes with exercise termination strongly suggests that they may play an important role in exercise limitation.Following maximal incremental cycling the majority of tidal breathing characteristics returned to pre-exercise values within 10 minutes of the end of exercise, including the rapid shallow breathing observed in a number of subjects, which has been associated with respiratory muscle fatigue. Subsequent trails showed that both the inspiratory and expiratory muscle's ability to produce maximum respiratory pressures was significantly impeded post exercise, probably due to respiratory muscle fatigue. Flow and volume characteristics of maximum exercise ventilation differed significantly from those obtained by the maximum voluntary ventilation manoeuvre, highlighting the inappropriateness of using the MVV as a measure of ventilatory capacity during exercise. Changes in respiratory system functions are reflected in changes in airflow profile. This thesis explores the use of profile measurements to detect and measure factors that limit exercise.
|Date of Award
|Edgar Williams (Supervisor)