Assessment of two methods to reduce simulated +Gz-induced arm pain using a non-centrifuge model

Complaints of +Gz-induced arm pain have been expressed by centrifuge subjects and, to a lesser degree, by high performance fighter pilots, usually when the control stick and throttle are positioned below heart level; the pain may be higher during pressure breathing for +Gz protection. Elevated transmural pressure and overdistension of the blood vessels in the arms have been suggested as causal factors. An earlier-developed non-centrifuge model was used to provoke arm pain similar to that induced by +Gz exposure. Eleven healthy subjects placed inside a hyperbaric chamber with an arm externalized through a sealed opening. They were exposed to chamber pressures at 75, 100 and 125 mmHg fitted with elastic bandage of the arm, or a localized pressure of 50 mmHg applied to the vessels of the upper arm or were provided no protection (control). Arm pain was estimated using a modified Borg scale. The sizes of the ulnar, radial and interosseous arteries, and corresponding veins, at the elbow level were measured using a sonographic imaging system. No statistically significant differences in pain were detected comparing control to proposed (counteracting) devices. There were no statistical differences in arm arterial or venous vessel size with the different devices at the different pressures. Thus, the devices tested did not show any protection against the provoked arm pain.