Muscle sympathetic outflow during horizontal linear acceleration in humans

To elucidate the effects of linear acceleration on muscle sympathetic nerve activity (MSNA) in humans, 16 healthy men were tested in a linear accelera tor. Measurements of MSNA, electrocardiogram, blood pressure, and thoracic impedance were undertaken during linear acceleration. Sinusoidal linear acc eleration with peak values at +/-0.10, +/-0.15, and +/-0.20 G was applied i n anteroposterior (+/-G(X), n = 10) or lateral (+/-G(y), n = 6) directions. The total activity and burst rate of MSNA decreased significantly during f orward, backward, left, or right linear accelerations. The total activity o f MSNA decreased to 50.56.9, 52.5 +/-4.4, 71.2 +/-9.6, and 67.6 +/-8.2% fro m the baselines (100%) during linear accelerations with peak values at +/-0 .20 G in the four directions, respectively. These results suggest that dyna mic stimulation of otolith organs in horizontal directions in humans might inhibit MSNA directly in order to quickly redistribute blood to muscles dur ing postural reflexes induced by passive movement, which supports the conce pt that the vestibular system contributes to sympathetic regulation in huma ns.