Sympathetic nerve response to muscle during anteroposterior acceleration in humans.

This study aimed to elucidate the effects of linear acceleration on muscle sympathetic nerve activity (MSNA) in humans. Eight healthy young male volunteers were seated in a linear accelerator (sled) during the recording of their electrocardiogram, blood pressure with the Finapres, thoracic impedance and respiration curve. MSNA was recorded from the tibial nerve by microneurography. At a fixed distance of sled movements in an anteroposterior direction, eight modes of stimulation with peak accelerations at 0.05, 0.10, 0.15, and 0.20 G (gravity) in sinusoidal or step mode were applied to each subject. Each movement was repeated for 5 cycles. Both the total activity and the burst rate of MSNA decreased during acceleration, and the level of the decrease was proportional to the level of the acceleration, whereas the average heart rate, thoracic impedance and mean arterial pressure did not change significantly. These results suggests that moderate linear acceleration may suppress MSNA in humans.