Cardiovascular responses and adaptations to breath-holding in humans

The aim of this thesis was to test the general hypothesis, that the end of phase II, i.e. the breaking of the steady state for cardiovascular variables, may coincide with the physiological breaking point of apnoea (Lin et al, 1974). This hypothesis was investigated by means of two, interrelated studies. Each of these studies analysed an experimental consequence of the general hypothesis, the one opposite with respect to the other. The first experimental consequence to be tested was that the duration of phase II and phase III would be shorter when apnoeas are carried out during light exercise than at rest because of the increase in metabolic rate in the former case. Of course, we expected to find the same values for cardiovascular variables at end of phase II at exercise as at rest, with similar characteristics during phase III. The testing of this hypothesis is the object of the first article, which is currently under revision at the European Journal of Applied Physiology. The second experimental consequence to be tested was that the duration of phase II and phase III would be longer when apnoeas are carried out when pure oxygen is breathed before apnoea instead of air, because of the increase in oxygen stores in the former case. Of course, we expected to find the same values for cardiovascular variables at end of phase II at exercise as at rest, with similar characteristics during phase III. The testing of this hypothesis is the object of the second article, which is currently under preparation.