Effects of acceleration in the Gz axis on human cardiopulmonary responses to exercise

The aim of this paper was to develop a model from experimental data allowing a prediction of the cardiopulmonary responses to steady-state submaximal exercise in varying gravitational environments, with acceleration in the Gz axis (ag) ranging from 0 to 3 g. To this aim, we combined data from three different experiments, carried out at Buffalo, at Stockholm and inside the Mir Station. Oxygen consumption, as expected, increased linearly with ag. In contrast, heart rate increased non-linearly with ag, whereas stroke volume decreased non-linearly: both were described by quadratic functions. Thus, the relationship between cardiac output and ag was described by a fourth power regression equation. Mean arterial pressure increased with ag non linearly, a relation that we interpolated again with a quadratic function. Thus, total peripheral resistance varied linearly with ag. These data led to predict that maximal oxygen consumption would decrease drastically as ag is increased. Maximal oxygen consumption would become equal to resting oxygen consumption when ag is around 4.5 g, thus indicating the practical impossibility for humans to stay and work on the biggest Planets of the Solar System.