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 (a _g) 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 a _g. In contrast, heart rate increased non-linearly with a _g, whereas stroke volume decreased non-linearly: both were described by quadratic functions. Thus, the relationship between cardiac output and a _g was described by a fourth power regression equation. Mean arterial pressure increased with a _g non linearly, a relation that we interpolated again with a quadratic function. Thus, total peripheral resistance varied linearly with a _g. 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 a _g is around 4.5 g, thus indicating the practical impossibility for humans to stay and work on the biggest Planets of the Solar System.