Howell, John Henry; (1996) The control of breathing during exercise in rowers. Doctoral thesis (Ph.D.), University College London.

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Abstract

The ventilatory response to exercise is well described in the literature, starting with an abrupt increase in ventilation coincident with the start of exercise. This is superseded some 20-40 seconds later by a more gradual rise, reaching steady-state some 3 to 5 min after the start of exercise. Despite considerable research throughout the last century, the mechanisms responsible for the control of breathing during exercise remain controversial. In 1963 Dejours published his neurohumoral hypothesis, whereby the initial increase is a response to neural stimuli and later increase is a response to humorally mediated stimuli. In this thesis I have addressed the following questions: 1. Highly trained athletes are reported to exhibit a large initial ventilatory response to the onset of exercise. Does the ventilatory response to exercise of highly trained sportsmen follow a similar profile to those reported in the literature for normal individuals? 2. Is exercise hyperpnoea a response to a neural and a humoral stimulus? 3. Is it possible to separate the ventilatory responses to the two stimuli by changing arterial Pco2? In addition I have addressed the following questions: Does pedal frequency affect a subject's exercise responses? Does the act of prior hyperventilation directly affect a subject's initial ventilatory response to the onset of exercise? Does lowering arterial Pco2 affect postural sway - a control mechanism with a subcortical CNS component? The results reported in this thesis support the view that CO2 plays a major part in the control of the ventilatory response to moderate intensity exercise. They raise questions concerning the origin of the stimulus responsible for the initial increase in ventilation seen on commencing exercise or following a step-increase in workload, and they highlight the effect of forewarning on the initial ventilatory and pulmonary gas exchange response to an increase in exercise intensity.

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