Background: Motion sickness is a common aeromedical problem that may occur in pilots exposed to increased gravitoinertial load in the head-to-foot direction (+Gz). Since motion sickness may affect autonomic nervous functions including cardiovascular control, it was hypothesized that it might interfere with cardiovascular responses to high +Gz, thereby decreasing G tolerance.
Methods: G tolerance and cardiovascular responses to increased G load were studied in nine subjects in a centrifuge environment under two conditions. In the motion sickness condition, the subject was exposed to a motion sickness provocation (MSP) comprising repeated rapid changes in G load in combination with a regimen of head movements. In the control condition the subject was exposed to similar cumulative G-time stress, but without the MSP. Mean arterial pressure (MAP) was measured. An index of peripheral vascular resistance was achieved by measuring the difference in skin temperature between the forearm and fingertip (deltaT(forearm-fingertip)).
Results: MSP decreased gradual-onset rate G tolerance from 5.1 +/- 1.0 G (mean +/- SD) to 4.6 +/- 0.9 G. There was no change in gradual-onset rate G tolerance in the control condition. Rapid-onset rate G tolerance was lower in the motion sickness (2.9 +/- 0.5 G) than in the control (3.4 +/- 0.3 G) condition. MSP reduced MAP by 11 mmHg and deltaT(forearm-fingertip) by 4.2 +/- 4.1 degrees C. In the control condition MAP and deltaT(forearm-fingertip) were unaffected.
Conclusions: Motion sickness may reduce the arterial pressure response to the extent that the capacity of an individual to withstand increased G loads in the head-to-foot direction is significantly diminished.