Role of carotid baroreflex and sympathetic responses in the push-pull effect: a simulation study

The push-pull maneuver (PPM) can lead to loss of consciousness in pilots of high-performance aircraft. This paper presents a mathematical model for the simulation of carotid baroreflex function and sympathetic responses during PPM.

The previous model was first modified by incorporating a submodel of the carotid baroreflex and then validated by comparing the simulation results with experimental data. Then the role of the carotid baroreflex was evaluated by varying the time delay and gain of the baroreflex independently during PPM and control runs, and the influence of different PPM profiles on sympathetic efferent activities were predicted.

Model outputs suggest that the effects of carotid baroreflex regulation with different time delays and gain factors on the push-pull effect (PPE) are almost the same as those on the control run. Meanwhile, simulation of sympathetic responses indicates that the frequency of spikes in the efferent sympathetic nerves increases with higher magnitude and longer duration of -Gz exposure, as well as with higher magnitude of +Gz exposure. However, the effect of changed sympathetic responses may be alleviated when transferred to baroreflex effectors.

The simulation results support that the carotid baroreflex and sympathetic responses might have little specific influences on the PPE. It also suggests that the limited range of G alteration and transition rate should be considered when using tilting experiments to investigate sympathetic response to PPE. The limitation of the present model due to the lack of sufficient data on the contribution of different peripheral vascular beds and their myogenic response is discussed.